This page shows what was measured, who it was measured in, and what that does not settle.
What Permethrin does in the body
Sodium keeps leaking in, the nerve never resets, and the mite or louse is paralysed and dies.
Nerves fire by letting sodium rush in through a gate and then slamming the gate shut so they can reset. Permethrin wedges that gate open. Insect gates are far more sensitive to it than human ones, and on top of that human skin absorbs almost none of it — about two per cent or less of what is applied — and breaks down what does get in within hours. That combination of a species-selective target and near-zero exposure is why a neurotoxic insecticide is safe enough to put on a baby.
Why people take it. Scabies, and head lice
What happened in people
Complete clearance at one week 65% on permethrin against an illustrative 43% on oral ivermectin (RR 0.65, 95% CI 0.54 to 0.78)
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The recorded finding that sits closest to something a person would notice. Written into the record, not signed off, and it carries no population or interval.
Only three permethrin products appear in the CMS survey, at a median United States acquisition cost of US$0.2314 per gram
Where it acts
The skin surface and the burrows in the stratum corneum where the scabies mite lives, and the scalp and hair shaft for lice
Kind of result
The kind of result is not recorded
Supervision
RNAWiki has not recorded a supervision or regulatory status for this substance.
What the registries record it as
The substance registry classes this as mixture.
FDA substance registry · 509F88P9SZ · read 2026-08-29
Its recorded molecular formula is C21H20Cl2O3, weighing 391.29.
US prescribing information · 35225d0a-3bde-4c7d-bdf9-81661012e77c · read 2026-08-30
Where each sentence above came from
A person wrote this explanation into the record, with the studies named in the path below.
The recorded use, written for a reader without medical training. Not signed off.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 135 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Comparator
A comparator is whatever the treatment was measured against.
A picture of it, and where the picture fails
It is like the other runner in a race.
Where that stops being true. A race has one winner. A study can show both arms improved.
What people get wrong. Results are read without asking what the other group got. Beating nothing is not beating a treatment.
The control condition against which the experimental intervention is assessed.
Randomisation
Randomisation means chance decides who gets which treatment.
A picture of it, and where the picture fails
It is like a coin toss deciding the groups.
Where that stops being true. A coin toss is fair once. Fairness here comes from doing it for everyone.
What people get wrong. It is thought to make groups identical. It makes them similar on average, including on things nobody measured.
Allocation of participants to arms by a chance process, so that unmeasured factors are balanced in expectation.
Absolute difference
An absolute difference is how many more people in a hundred were affected.
A picture of it, and where the picture fails
It is like counting heads in two rooms of a hundred.
Where that stops being true. Heads are easy to count. Study results carry a margin of error too.
What people get wrong. It is confused with a percentage change, which can look far larger.
The arithmetic difference in event rates between arms.
Confidence interval
A confidence interval is the range the true answer is likely to sit in.
A picture of it, and where the picture fails
It is like a weather forecast giving a range rather than one number.
Where that stops being true. A forecast range covers tomorrow. This one covers what the study could resolve.
What people get wrong. The middle number is read as the answer. A range crossing zero means no change is still possible.
An interval estimate that would contain the true parameter in a stated proportion of repeated studies.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
Complete clearance of scabies one week after treatment
✓ The study showed what it set out to show
Who was studied
Cochrane pooled permethrin against ivermectin, one week (CD012994)
How many people
613
Study design
Systematic review and meta-analysis of randomised controlled trials
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
RR 0.65 (95% CI 0.54 to 0.78) favouring permethrin, 6 studies, low-certainty evidence; illustrative clearance 65% permethrin against 43% ivermectin
Repeated elsewhere
Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Nearly all included trials were run in South Asia or North Africa. Risk of bias was moderate and reporting poor in many studies, which the reviewers name as their major limitation.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Topical cream 5% for scabies; over-the-counter creme rinse 1% for head lice
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Permethrin Cream 5% United States prescribing information, Indications and Usage and Clinical Pharmacology — NDA 019855, retrieved from the openFDA label end… · a recorded source, not a stored snapshot
Complete clearance four weeks after initiation, one to three applications or doses
✗ The study did not show it
Who was studied
Cochrane pooled permethrin against ivermectin, four weeks (CD012994)
How many people
581
Study design
Systematic review and meta-analysis of randomised controlled trials
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
RR 0.92 (95% CI 0.82 to 1.03), 5 studies, low-certainty evidence; illustrative cures 93% permethrin against 86% ivermectin — no difference detected
Repeated elsewhere
Replicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. The reviewers state that for the most part no difference in efficacy was detected between permethrin and either form of ivermectin. The week-one advantage does not persist.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Topical cream 5% for scabies; over-the-counter creme rinse 1% for head lice
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Permethrin Cream 5% United States prescribing information, Indications and Usage and Clinical Pharmacology — NDA 019855, retrieved from the openFDA label end… · a recorded source, not a stored snapshot
Prevalence of scabies treatment failure and its associated factors
Systematic review and random-effects meta-analysis of 147 studies, 1983 to 2021
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Overall failure 15.2% (95% CI 12.9 to 17.6, I² = 95.3%); permethrin 10.8% (7.5 to 14.5); permethrin failure rising 0.58% per year across the study period
Repeated elsewhere
Partially Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Only three of 147 studies performed a multivariable risk factor analysis and none assessed resistance. Sample size here counts studies, not participants — participant-level totals are not reported as a single figure.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Topical cream 5% for scabies; over-the-counter creme rinse 1% for head lice
Interval reported. 95% CI 12
Written into the record, not signed off as a reviewed claim.
Permethrin Cream 5% United States prescribing information, Indications and Usage and Clinical Pharmacology — NDA 019855, retrieved from the openFDA label end… · a recorded source, not a stored snapshot
Frequency of pyrethroid knockdown-resistance alleles in treated head louse populations
✓ The study showed what it set out to show
Who was studied
Pyrethroid resistance frequency meta-analysis in head lice (PMID 34935614)
How many people
24
Study design
Systematic review and meta-analysis of 24 field surveys, 2000 to June 2021
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Mean resistance frequency 76.9%; 64.4% of resistant lice homozygous and 30.3% heterozygous; 100% allele frequency reported in four countries
Repeated elsewhere
Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Sample size counts included articles rather than lice. Surveys are geographically uneven and the review restricted itself to English-language publications.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Topical cream 5% for scabies; over-the-counter creme rinse 1% for head lice
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Permethrin Cream 5% United States prescribing information, Indications and Usage and Clinical Pharmacology — NDA 019855, retrieved from the openFDA label end… · a recorded source, not a stored snapshot
What we know
RNAWiki holds 4 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
Permethrin
What a person takes: Topical cream 5% for scabies; over-the-counter creme rinse 1% for head lice.
The measurement behind this step
A lipophilic cream that partitions into the stratum corneum and the mite burrows within it, killing on contact rather than requiring the parasite to feed. Percutaneous absorption is 2% or less of a single application, and what is absorbed is hydrolysed to inactive metabolites and excreted in urine. The 1% creme rinse is a short-contact scalp product for a different parasite.
Getting in
Applied to skin, and barely absorbed
The cream goes on the skin where the mites are. Almost none of it crosses into the body — two per cent or less of what is applied.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
The label reports absorption of 2% or less of a single application of the 5% cream, from carbon-14 labelled studies and from patients with moderate to severe scabies. Permethrin is rapidly metabolised by ester hydrolysis to inactive metabolites excreted primarily in urine.
The mite lives in burrows in the outer skin, which is exactly where a lipophilic cream sits. The drug crosses the mite’s cuticle and reaches its nervous system.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Permethrin is highly lipophilic and partitions into the stratum corneum and the burrows within it. Penetration into the arthropod occurs through the cuticle rather than by ingestion, which is why the drug works on contact rather than requiring feeding.
Nerve cells fire by letting sodium in and then shutting the gate. Permethrin stops the gate closing.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Permethrin binds a lipophilic site on the arthropod voltage-gated sodium channel and slows inactivation, prolonging the open state. The label describes it as disrupting the sodium channel current by which polarisation of the membrane is regulated.
The nerve cannot reset and the animal is paralysed
With sodium leaking in continuously the nerve never repolarises. The mite or louse is knocked down and dies.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Delayed repolarisation and paralysis are the stated consequences in the label. Human channels are far less sensitive, mammalian body temperature reduces pyrethroid binding, and mammalian esterases hydrolyse the ester rapidly — three independent contributions to selectivity.
Lice have accumulated changes in that gate which stop the drug binding. Across worldwide surveys about three-quarters of lice carry them, and in four countries all of them do.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Knockdown resistance arises from point substitutions in the voltage-gated sodium channel that reduce pyrethroid binding without impairing normal channel function. Pooled mean frequency across 24 studies was 76.9%, with 64.4% of resistant lice homozygous, and 100% allele frequency reported in Australia, England, Israel and Turkey.
Every trial counts whether mites can still be found. None of them measured the itch, which is what the patient came in about and which continues for weeks after the last mite is dead.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Complete clearance of scabies was the primary outcome of every trial in the Cochrane review; post-scabetic pruritus appears in none of the outcome sets. The 147-study failure review records that no study assessed resistance either, so the two most likely explanations for a treatment appearing not to work are both unmeasured.
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 6 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
People with scabies, and their household contacts; and children and adults with head lice, for whom the 1% product is sold off the shelf.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What the label states about particular groups
On pediatric, the label states: “Safety and effectiveness in infants less than two months of age have not been established.”
US prescribing information · 35225d0a-3bde-4c7d-bdf9-81661012e77c · read 2026-08-30
On older people, the label states: “Clinical studies of Permethrin Cream 5% w/w did not identify sufficient numbers of subjects aged 65 and over to allow a definitive statement regarding whether elderly subjects respond differently from younger subjects.”
US prescribing information · 35225d0a-3bde-4c7d-bdf9-81661012e77c · read 2026-08-30
On people who are pregnant, the label states: “Teratogenic Effects: Pregnancy Category B Reproduction studies have been performed in mice, rats, and rabbits (200 to 400 mg/kg/day orally) and have revealed no evidence of impaired fertility or harm to the fetus due to permethrin.”
US prescribing information · 35225d0a-3bde-4c7d-bdf9-81661012e77c · read 2026-08-30
On people who are breastfeeding, the label states: “It is not known whether this drug is excreted in human milk.”
US prescribing information · 35225d0a-3bde-4c7d-bdf9-81661012e77c · read 2026-08-30
Where the result stopped carrying
The week-one advantage over ivermectin disappears by week two and is gone at four weeks
Permethrin failure prevalence has climbed steadily for nearly four decades of published studies
Against head lice the resistance allele is now the majority allele in surveyed populations, and fixed in four countries
No study in the 147-study failure review assessed resistance, so the most important question about the drug has no direct data behind it
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (11)
It was studied for a different goal
The studies measured something else entirely. Nothing in this record points to this reason.
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Prescription only
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Topical cream 5% for scabies; over-the-counter creme rinse 1% for head lice
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
RNAWiki has not recorded a supervision or regulatory status for this substance.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
No register row and no identity class settled the question.
No source is stored against this line.
What is in the pack
A lipophilic cream that partitions into the stratum corneum and the mite burrows within it, killing on contact rather than requiring the parasite to feed. Percutaneous absorption is 2% or less of a single application, and what is absorbed is hydrolysed to inactive metabolites and excreted in urine. The 1% creme rinse is a short-contact scalp product for a different parasite.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
Well tolerated: in the pooled randomised trials at four weeks, the extrapolated proportion with at least one adverse event was 4% on permethrin against 5% on ivermectin, and no withdrawals for adverse events occurred in either group. Reporting of adverse events in the underlying studies was described by the reviewers as suboptimal. Transient burning, stinging and itching on application are the usual complaints, and are hard to distinguish from the itch of the disease. The selectivity that makes a neurotoxic insecticide acceptable on human and infant skin rests on the arthropod channel’s greater sensitivity, the temperature dependence of pyrethroid binding and rapid mammalian ester hydrolysis.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Topical cream 5% for scabies; over-the-counter creme rinse 1% for head lice
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
Percutaneous absorption is 2% or less of a single application, and what is absorbed is hydrolysed to inactive metabolites and excreted in urine. The 1% creme rinse is a short-contact scalp product for a different parasite.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on which forms are sold and how they compare.
No source is stored against this line.
What is recorded as being sold
21 products list this as an active ingredient in the United States drug directory. 21 of them contain it and nothing else.
FDA National Drug Code directory · 87544-8526 · read 2026-08-29
They are sold as cream, liquid, lotion, powder and rinse, taken oral and topical.
FDA National Drug Code directory · 87544-8526 · read 2026-08-29
The regulator's established pharmacologic class for it is pyrethrins [cs] and pyrethroid [epc].
FDA National Drug Code directory · 87544-8526 · read 2026-08-29
17 published labels name it as an active ingredient. 17 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 79a1a246-4846-48b1-b95d-f8ce1ebf9c8f · read 2026-08-29
Those labels are classed as human otc drug and human prescription drug.
US prescribing information · 79a1a246-4846-48b1-b95d-f8ce1ebf9c8f · read 2026-08-29
Permethrin is topical at HOW SUPPLIED Permethrin Cream 5% w/w is available as follows: 60 g tube ( NDC 21922-021-07)., recorded as fda label in effect 2025-10-09 in the United States.
US prescribing information · 35225d0a-3bde-4c7d-bdf9-81661012e77c · read 2026-08-30
Recorded price in US: 0.23144 USD per one gram, across 3 priced products whose strengths and pack forms differ, as of 2026-08-26, paid by retail pharmacies buying the product, as surveyed by the Centers for Medicare & Medicaid Services. It is not a list price, an insurance price, or what anyone pays at a counter..
Recorded source · 2026-08-26 · read 2026-08-28
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
RNAWiki could not confidently classify this substance, so no self-experiment plan is offered.
Questions worth asking
Which of the trials of Permethrin studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That parasitological clearance is what the patient experiences as cure, when the itch persists for weeks afterwards and no trial measured it
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That continued over-the-counter availability for head lice implies continued effectiveness against them
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That a pooled clearance rate from South Asian and North African trials transfers to regions whose failure rates differ significantly
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That the rising failure rate is resistance — the authors call it a hint, and none of the 147 studies tested for it
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of Permethrin are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
Faster than ivermectin in week one, level with it by week two
In plain words
Fifteen randomised trials compared permethrin cream against ivermectin. After a week, roughly two-thirds of the permethrin patients were clear against four in ten on ivermectin. By two weeks the gap had closed, and by four weeks both were above eighty-five per cent.
What was measured
Complete clearance of scabies at one, two and four weeks, permethrin against ivermectin
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The 2018 Cochrane review included 15 studies with 1,896 participants comparing topical permethrin, systemic ivermectin and topical ivermectin. Using the average clearance of 65% in the permethrin trials, the illustrative clearance with oral ivermectin at one week was 43% (RR 0.65, 95% CI 0.54 to 0.78; 613 participants, 6 studies, low-certainty evidence). By two weeks there may be little or no difference (74% against 68%; RR 0.91, 95% CI 0.76 to 1.08; 459 participants, 5 studies). With one to three doses or applications at four weeks, illustrative cures were 93% for permethrin and 86% for ivermectin (RR 0.92, 95% CI 0.82 to 1.03; 581 participants, 5 studies). The authors conclude that for the most part no difference in efficacy was detected, with confidence in the effect estimates mostly low to moderate and poor reporting a major limitation.
Written into the record, not signed off as a reviewed claim
Failure rates have risen every year since 1983, and nobody has tested for resistance
In plain words
A review of 147 studies found that about one scabies treatment in seven fails, and that permethrin failures have crept up by roughly half a percentage point every year for four decades. Not one of the 147 studies looked for resistance in the mite.
What was measured
Pooled treatment failure prevalence and its annual trend, 1983 to 2021, across 147 studies
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The overall prevalence of scabies treatment failure across 147 eligible studies was 15.2% (95% CI 12.9 to 17.6; I² = 95.3%, moderate-certainty evidence), with regional variation (P=0.003) and the highest rate in the Western Pacific region at 26.9% (95% CI 14.5 to 41.2). Permethrin failure was 10.8% (95% CI 7.5 to 14.5), oral ivermectin 11.8% (8.4 to 15.4) and topical ivermectin 9.3% (5.1 to 14.3). Across the included studies from 1983 to 2021, overall failure prevalence increased by 0.27% per year and permethrin failure prevalence by 0.58% per year. Only three studies conducted a multivariable risk factor analysis, and the review records that no studies assessed resistance. The authors read the temporal increase as a hint of decreasing mite susceptibility.
Written into the record, not signed off as a reviewed claim
Against head lice, the resistance mutation is now the majority allele
In plain words
Permethrin is still sold off the shelf as the standard treatment for head lice. Across twenty-four surveys worldwide, three-quarters of lice carried the mutation that makes them insensitive to it, and in four countries every louse tested did.
What was measured
That an over-the-counter treatment’s continued availability implies continued effectiveness — the pooled resistance frequency in the target organism is 76.9% and reaches 100% in four surveyed countries
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A systematic review and meta-analysis of 24 articles covering the period 2000 to June 2021 estimated the mean frequency of pyrethroid resistance in treated head louse populations at 76.9%, of which 64.4% of resistant lice were homozygous and 30.3% heterozygous. Four countries — Australia, England, Israel and Turkey — showed 100% knockdown-resistance gene frequencies, which the authors state is likely to render pyrethrin- and pyrethroid-based pediculicides ineffective there. The highest resistance recorded across the included studies was against permethrin specifically. The mechanism is target-site insensitivity: point substitutions in the voltage-gated sodium channel that reduce pyrethroid binding without affecting the channel’s normal function.
Written into the record, not signed off as a reviewed claim
The safety case is a pharmacokinetic number, and the label states it
In plain words
Putting an insecticide on a child’s skin sounds alarming until you see how little of it gets in. The label says two per cent or less of a single application is absorbed, and what does get in is broken down and passed in urine.
What was measured
Percutaneous absorption of 2% or less of a single application, from carbon-14 labelled studies
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The permethrin cream 5% label states that although the amount absorbed after a single application has not been determined precisely, data from studies with carbon-14 labelled permethrin and absorption studies of the cream applied to patients with moderate to severe scabies indicate it is 2% or less of the amount applied. Permethrin is rapidly metabolised by ester hydrolysis to inactive metabolites excreted primarily in the urine. Selectivity has three independent components: the arthropod sodium channel is markedly more sensitive than the mammalian one, pyrethroid binding falls with rising temperature so mammalian body temperature works against it, and mammalian esterases cleave the molecule quickly. Any one of those alone would be a thin argument; together they are why the drug is usable on infants.
Source
Permethrin Cream 5% United States prescribing information, Clinical Pharmacology (NDA 019855, openFDA label endpoint)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
verified
Review state
Written into the record, not signed off as a reviewed claim
The trials were run where the disease is, which is not where the guidelines are used
In plain words
Nearly every randomised trial in the Cochrane review was conducted in South Asia or North Africa, where scabies is common and associated with poverty. The results are then applied worldwide, including in settings with different mite populations and different living conditions.
What was measured
That a pooled clearance rate from trials in South Asia and North Africa describes what will happen elsewhere, when the pooled failure rate itself differs significantly by region
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The review records that nearly all included studies were conducted in South Asia or North Africa, where the disease is more common and is associated with poverty; that the overall risk of bias in included trials was moderate with poor reporting in many studies; and that confidence in the effect estimates was mostly low to moderate, with poor reporting a major limitation. The treatment-failure review separately found significant regional differences in failure prevalence between World Health Organization regions (P=0.003), with the Western Pacific at 26.9% against an overall 15.2%. Transporting a pooled clearance rate across regions that demonstrably differ by a factor of nearly two is an inference the trials do not license.
Written into the record, not signed off as a reviewed claim
Nothing in these trials measured the symptom people actually have
In plain words
Scabies is unbearable because of the itch. The primary outcome in every one of these trials is whether mites can still be found. The itch is an allergic reaction that continues for weeks after the last mite dies, and it is not what was measured.
What was measured
That parasitological clearance is what a scabies patient experiences as cure — the itch is an immune response to dead mite material and persists for weeks after clearance, and no trial in the review measured it
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Cochrane review’s primary outcome was complete clearance of scabies, with secondary outcomes of re-treatment, adverse events and withdrawals. Post-scabetic pruritus is not among them. Reporting of adverse events in included studies was described as suboptimal; at four weeks the extrapolated proportion with at least one adverse event was 4% for permethrin and 5% for ivermectin (RR 1.30, 95% CI 0.35 to 4.83, low-certainty evidence). Because persistent itch is routinely interpreted as treatment failure by patients and sometimes by clinicians, an endpoint that excludes it also systematically under-measures the thing that drives re-treatment.
This order is fixed in code and does not count clicks or time on the page.
What is not here
7 questions this page could not answer
These sections were prepared and left out because there was nothing to put in them. They are listed rather than hidden, so the gaps in this record are visible.
What was measured, goal by goal — found nothing in the sources checked.
How close this is to real life — found nothing in the sources checked.
Felt, measured, or meaningful — found nothing in the sources checked.
How long anything takes — found nothing in the sources checked.
What it may clash with — found nothing in the sources checked.
Other ways to the same goal — found nothing in the sources checked.
What changed on this page — found nothing in the sources checked.
The record as stored
The full record, for auditing
Everything above is built from what is below. This layer keeps the technical vocabulary, record identifiers and every stored row, so a reader who wants to check the page can.
The older medicine-wide conclusion held in this record
Written for a clinical reader, and about the medicine as a whole rather than about one indication, population and set of trials. RNAWiki does not treat it as a programme conclusion and no reviewer has signed it off in that form. It is here word for word because it is what the record holds.
A synthetic pyrethroid that holds the arthropod sodium channel open until the nerve cannot fire again — indistinguishable from ivermectin on complete clearance of scabies by two weeks across 15 randomised trials in 1,896 people, with a pooled treatment failure rate of 10.8% that has risen by about half a percentage point every year since 1983, and facing a head louse population whose pooled resistance-mutation frequency is 76.9%.
"After year 1, there was insufficient statistical power to detect a difference in the primary outcome measure during planned study period."; 2 of 14 registered studies
Show the evidence
Trial
NCT00958139
terminated; "After year 1, there was insufficient statistical power to detect a difference in the primary outcome measure during planned study period."
NCT02500524
terminated; "Lack of efficacy"
recorded 2026-09-01 · last checked 2026-09-04
Q4
Human studies of Permethrin used permethrin (5%) — over how long?
Human studies of Permethrin used "permethrin (5%)". ClinicalTrials.gov · 2026-09-01
3 recorded entries; human; also "Permethrin Cream, 5%", "Elimite™ Cream (permethrin) 5%"
Show the evidence
human
NCT02213055
permethrin (5%)
NCT02978508
Permethrin Cream, 5%
NCT03178942
Elimite™ Cream (permethrin) 5%
recorded 2026-09-01 · last checked 2026-09-04
Q5
Which 6 trials of Permethrin posted no result?
Posted no result
6 of 6 completed trials
Registrations
NCT02572986, NCT05362513, NCT02407782, NCT05862701, NCT06396507 and NCT05819983
Completion dates
oldest 2016-08; newest 2023-03-06
Show the evidence
Trial
NCT02572986
2016-08
NCT05362513
2021-11-30
NCT02407782
2022-01-18
NCT05862701
2022-09-30
NCT06396507
2022-11-12
NCT05819983
2023-03-06
Q6
At the median, Permethrin's trials enrolled 190 people — anything larger?
Median enrolment
190
Largest enrolment
1291
Registered trials counted
14
Where it is registeredIdentifiers, relations and other names
ClinicalTrials.gov — US Government work · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
✗ required summary fields resolved: 4 required field(s) not terminal: Why people use it, Best-supported result, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 5 source rows
✓ no critical contamination: no quarantine open
✓ canonical metadata passed: slug and display name present
✓ no raw internal fields: enforced by the copy-contract test over the rendered page
This is a record of evidence. It is not medical advice, and it does not say this substance suits you. Nothing here says any substance on RNAWiki is appropriate for a child.