After how many days should you re‑treat the head for lice? - briefly
The second application is normally scheduled 7–10 days after the initial treatment, commonly on day 9. This timing targets newly hatched nits before they mature.
After how many days should you re‑treat the head for lice? - in detail
The life cycle of head‑lice consists of egg (nit), nymph and adult stages. Eggs hatch in about 7‑10 days, and nymphs become sexually mature within an additional 3‑4 days. Because most pediculicides cannot penetrate the protective shell of an egg, a single application eliminates only the live insects present at the time of treatment. Consequently, a second dose is required to target the newly emerged nymphs before they reach reproductive maturity.
Clinical guidelines and product instructions recommend a follow‑up treatment 7 days after the first application. This timing ensures that any hatchlings are still vulnerable and have not yet produced new eggs. Some manufacturers extend the interval to 9‑10 days to accommodate variations in temperature and hair length that may delay hatching.
A practical protocol includes:
- Apply the first treatment according to label directions, ensuring thorough coverage of the scalp and hair.
- Wait exactly seven days, then repeat the application using the same product or a prescribed alternative if resistance is suspected.
- Perform a nit combing session 24 hours after each treatment to remove dead insects and any remaining eggs.
- Inspect the scalp daily for at least two weeks; if live lice are observed after the second dose, a third application may be warranted after another seven‑day interval, following medical advice.
Prescription options such as oral ivermectin or topical spinosad may follow a different schedule, typically a single dose with a possible repeat after 7 days if infestation persists. Resistance to pyrethrin‑based products has increased, making the timing of the second application critical for successful eradication.