When do lice die after treatment? - briefly
Most lice are eliminated within 24 hours of a correctly applied pediculicide, and any surviving nymphs typically die by the following day. Eggs remain viable and usually need a repeat treatment after 7–10 days.
When do lice die after treatment? - in detail
Effective pediculicide formulations eliminate adult head‑lice within a few hours. Most synthetic pyrethroids (permethrin, pyrethrin) achieve 100 % mortality in 6–8 hours after proper application. Malathion, a higher‑dose organophosphate, kills lice in 4–6 hours, but resistance may prolong the interval. Ivermectin lotion reaches complete kill in 8–10 hours; spinosad shampoo works in 5–7 hours. Dimethicone‑based products, which physically coat the insect, cause death in 8–12 hours without chemical toxicity.
Nits (unhatched eggs) are not affected by most insecticides. A viable egg requires about 7–10 days to hatch at typical scalp temperatures. Consequently, a second treatment is recommended 7–9 days after the first application to eradicate newly emerged lice before they reproduce.
Key points for each treatment class:
- Pyrethroid lotions/shampoos – adult death 6–8 h; repeat in 7 days.
- Organophosphate (malathion) – adult death 4–6 h; repeat in 7 days; monitor for resistance.
- Ivermectin lotion – adult death 8–10 h; repeat in 7 days.
- Spinosad shampoo – adult death 5–7 h; repeat in 7 days; minimal resistance reported.
- Dimethicone (silicone‑based) – adult death 8–12 h; repeat in 7 days; safe for sensitive skin.
Factors that can modify these intervals include scalp temperature, hair length, product concentration, and thoroughness of application. Inadequate coverage or premature rinsing can extend the time to kill lice, potentially leaving survivors that resume egg‑laying within 24 hours.
The life‑cycle timeline clarifies why a single application rarely eliminates an infestation: adult lice live 30–35 days, lay eggs within 24 hours of reaching adulthood, and each egg hatches after 7–10 days. Immediate killing of adults halts new egg production, but existing eggs require the scheduled follow‑up to prevent resurgence.
In practice, observe the scalp 24 hours after treatment for dead insects; absence of live lice confirms efficacy. Inspect the hair at day 7–9 for any live nits; if none are found, the infestation is considered resolved. If live lice are detected, repeat the treatment according to the product’s instructions and verify proper application technique.