Permethrin
Is It Right for You?
A complete guide to Permethrin — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Permethrin?
Permethrin is a synthetic pyrethroid insecticide and antiparasitic agent available as a 5% cream (for the treatment of scabies) and a 1% cream rinse or lotion (for the treatment of head lice). It works by acting directly on the nervous system of parasites — disrupting sodium channel function and causing paralysis and death of the mite or louse and its eggs.
Permethrin 5% cream (Lyclear 5% Dermal Cream) is the recommended first-line treatment for scabies in the UK, as advised by NICE and PHE guidelines, and is considered highly effective, safe, and well tolerated in most patient groups. Permethrin 1% cream rinse is used for the treatment of head lice infestation.
Permethrin 5% cream is a prescription-only medication in the UK. The 1% preparation for head lice is available over the counter. A clinician should confirm the diagnosis before prescribing the 5% treatment for scabies, as correct application technique and treatment of all household contacts simultaneously is critical to eradication.
What Conditions Is Permethrin Used For?
Permethrin is indicated for:
infestation caused by the mite Sarcoptes scabiei; first-line treatment for all age groups from 2 months of age (5% cream)
a highly contagious variant causing hyperkeratotic crusted skin lesions; requires multiple applications under specialist guidance, often in combination with oral ivermectin
infestation caused by Pediculus humanus capitis; 1% cream rinse or lotion used as first- or second-line topical treatment
Scabies spreads through prolonged skin-to-skin contact. Treating only the index patient while household and close physical contacts remain untreated leads to rapid reinfestation. All individuals in the same household or those who have had prolonged skin contact within the preceding 6–8 weeks must be treated simultaneously on the same day — regardless of whether they have symptoms.
How Does Permethrin Work?
Permethrin is a synthetic derivative of pyrethrin (a natural insecticide from chrysanthemum flowers). Its antiparasitic mechanism is highly selective for arthropod nervous systems:
Voltage-gated sodium channel disruption: In the peripheral nerve membranes of insects and arachnids (including the scabies mite and body/head lice), permethrin binds to voltage-gated sodium channels and holds them in an open state, preventing the channel from closing (inactivation) after depolarisation. This causes prolonged, repetitive nerve firing — the equivalent of a continuous electrical storm in the parasite's nervous system — followed by paralysis and death.
Selectivity for arthropods over mammals: Mammalian voltage-gated sodium channels are far less sensitive to permethrin due to structural differences in the channel protein. Additionally, mammals can rapidly metabolise permethrin via hepatic esterases, further reducing systemic toxicity. This large differential in sensitivity and metabolism accounts for permethrin's excellent safety profile in humans when used as directed.
Ovicidal activity: Permethrin is both pediculicidal (kills lice and mites) and ovicidal (kills eggs), making it highly effective as a single-application treatment when used correctly, in contrast to older insecticides that required multiple applications.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
For scabies — whole-body application is non-negotiable. The most common reason for treatment failure is incomplete application. Cover every skin surface from the jaw line downwards — including the scalp and face in infants, elderly, and immunocompromised patients; the soles of the feet; under fingernails and toenails; the genital area; and all skin folds. Do not miss areas.
Apply to cool, dry skin. Hot skin or skin immediately after a hot bath increases absorption; apply after a cool shower and allow skin to dry before application.
Treat all household contacts on the same day. Prescriptions for all eligible contacts should be arranged simultaneously. Even asymptomatic contacts harbour mites and will reinstate the cycle of infestation.
Wash and change bedding and clothing. On the day of treatment, wash all clothing, bed linen, and towels in a washing machine on a hot cycle (at least 50°C) or seal items in a plastic bag for 72 hours.
Itch may persist for up to 4 weeks after successful treatment due to the ongoing immune response to mite proteins. This does not indicate treatment failure; a short course of a soothing antihistamine or mild topical corticosteroid can help manage post-scabetic itch.
Side Effects of Permethrin
Most side effects are mild and resolve on their own. Serious side effects are rare but require immediate medical attention.
- Local burning, stinging, tingling, or itching at the application site --- common and usually transient
- Mild erythema (redness) at treated skin areas
- Temporary worsening of itch in the first 48–72 hours after treatment for scabies --- expected and not a sign of treatment failure
- Severe allergic hypersensitivity reaction --- urticaria, angioedema, rash, or anaphylaxis; rare but possible in patients sensitised to pyrethroids or pyrethrins; seek immediate emergency care
- Severe skin irritation or chemical burn --- rare; with prolonged contact or application to broken skin
- Accidental eye exposure --- causes significant ocular irritation; flush immediately with copious water
- Ingestion --- permethrin cream is for external use only; accidental ingestion can cause nausea, vomiting, and neurological symptoms; seek emergency care
Itch following permethrin treatment of scabies can persist for 3–4 weeks after successful eradication. This is a normal immune response to dead mite proteins and burrows remaining in the skin. Persistent itch alone is not an indication for re-treatment. Re-treatment should only be considered if live mites are identified or if new burrows or typical lesions appear after 4 weeks.
Drug Interactions
Permethrin has negligible systemic absorption from correctly applied topical formulations, meaning significant pharmacokinetic interactions with systemic drugs are not expected. However, do not apply other creams or emollients immediately before permethrin application as they may dilute and reduce efficacy.
no clinically significant interactions with other topical preparations when used as directed; do not apply other creams or emollients immediately before permethrin application as they may dilute and reduce efficacy.
negligible systemic absorption from correctly applied topical permethrin means significant pharmacokinetic interactions with systemic drugs are not expected.
Important Warnings
Treating the index case alone without treating all household and close physical contacts on the same day is the principal cause of scabies treatment failure. This is not optional — it is the most important determinant of successful eradication.
Permethrin 5% cream should be used with caution in infants under 2 months of age; the facial and scalp application recommended in infants must be approached carefully to avoid contact with the eyes and mouth. Seek specialist guidance for neonatal scabies.
Patients with known hypersensitivity to pyrethrin or permethrin should not use permethrin products. Alternative scabicidal treatments (e.g., malathion 0.5%, or oral ivermectin under specialist direction) should be discussed with the clinician.
Permethrin is generally considered low risk in pregnancy and breastfeeding due to minimal systemic absorption. It is the preferred scabies treatment in pregnancy. Avoid application to the breast area if breastfeeding; apply after feeding and wash off before the next feed. Seek clinician guidance.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Permethrin FAQs
Post-scabetic itch lasting 3–4 weeks after treatment is entirely expected and normal. The itch is caused by the immune system reacting to dead mite bodies and their protein debris still present in the skin — not by ongoing infestation. It does not mean the treatment has failed. Managing with a mild antihistamine (such as cetirizine) or a mild topical corticosteroid for the itch is appropriate; re-treatment should only be considered if new burrows or live mites are found after 4 weeks.
Yes — this is not optional. Scabies mites can be present on contacts for 4–6 weeks before symptoms develop. Treating only symptomatic individuals and not asymptomatic contacts will result in reinfestation within days. All household members and anyone who has had prolonged skin-to-skin contact must be treated simultaneously on the same day.
If symptoms persist or new burrows appear more than 4 weeks after correctly applied permethrin treatment (treating all contacts simultaneously), the most likely explanations are reinfection from an untreated contact, incomplete application, or — less commonly — reduced permethrin sensitivity. A clinician will reassess and may recommend a repeat course, alternative agents (malathion), or oral ivermectin, which is used under specialist guidance for resistant or crusted scabies.
The presence of new burrows (thin, thread-like lines in the skin, typically between the fingers, on the wrists, or around the genitals) or new typical rash after 4 weeks post-treatment indicates active infestation requiring re-treatment. Itch alone in the first 4 weeks, without new burrows or lesions, does not indicate persistent infection.
Yes. Permethrin 5% cream has minimal systemic absorption and is the recommended first-line treatment for scabies in pregnant women. It is preferred over alternatives with greater systemic exposure. Always inform your clinician that you are pregnant so they can confirm this is the most appropriate treatment for your individual circumstances.