How to Apply Permethrin Lotion
Apply permethrin 1% lotion to damp, freshly shampooed (with non-conditioning shampoo) and towel-dried hair, leave on for 10 minutes, then rinse off thoroughly. 1, 2
Pre-Application Preparation
Shampoo hair first with a non-conditioning shampoo before applying permethrin, as conditioners and silicone-based additives in regular shampoos impair permethrin adherence to the hair shaft and reduce its residual protective effect. 1
Towel-dry the hair after shampooing so it is damp but not dripping wet. 1, 2
Application Technique
Apply the permethrin 1% lotion thoroughly to all areas of the scalp and hair, ensuring complete coverage from roots to ends. 1
Leave the lotion on for exactly 10 minutes before rinsing. 1, 2
Rinse thoroughly with water after the 10-minute contact time. 1
Critical Re-Treatment Schedule
Repeat the application in 7-10 days (preferably on day 9) to kill newly hatched nymphs, as permethrin only kills 70-80% of eggs with the first application. 1, 2
Many experts now recommend routine re-treatment on day 9 even if no live lice are visible, rather than waiting to see if lice reappear. 1
An alternate treatment schedule of days 0,7, and 13-15 has been proposed for products with lower ovicidal activity. 1
Common Pitfalls to Avoid
Do not use conditioning shampoos before or immediately after permethrin application, as this is a major cause of treatment failure that is often mistaken for resistance. 1
Do not skip the second application at 7-10 days, as this is essential for killing nymphs that hatch from eggs that survived the first treatment. 1, 2
Itching after treatment is common and does not indicate treatment failure; it can persist for weeks due to sensitization and is not a reason for re-treatment unless live lice are found. 2
Safety Considerations
Permethrin has extremely low mammalian toxicity and is the least toxic pediculicide available. 1
Adverse effects are minimal, typically limited to mild pruritus, erythema, or edema at the application site. 1
Permethrin does not cause allergic reactions in individuals with plant allergies, unlike pyrethrin products. 1
Safe for pregnant and lactating women, making it the preferred treatment in these populations. 1, 2
When Treatment Fails
Consider improper application as the first cause of treatment failure before assuming resistance, particularly failure to use non-conditioning shampoo or skipping the second application. 2
Resistance to permethrin has been reported but prevalence is unknown in most areas. 1, 2
If treatment fails despite correct use, consider alternative agents such as malathion 0.5% or oral ivermectin. 2