When should you repeat a lice treatment? - briefly
Repeat the treatment 7–10 days after the initial application, when newly hatched nymphs emerge, and apply a third dose a week later if any live lice are still present.
When should you repeat a lice treatment? - in detail
A second application of a pediculicide is essential because eggs (nits) survive the initial spray. The follow‑up should be timed to intercept hatching cycles and to eliminate any newly emerged lice before they reproduce.
- Standard interval: 7–10 days after the first dose. This window matches the average 9‑day incubation period; most nits hatch within 7–9 days, and a repeat treatment at day 9 kills the emerging nymphs before they can lay eggs.
- Early repeat: If the first product is a wet‑comb (no insecticide), a second combing session is recommended after 48 hours, then again at day 7 and day 14, to remove any live insects that escaped the initial session.
- Late repeat: If the first treatment was applied later than 48 hours after discovering lice, wait at least 5 days before the second dose to ensure that any surviving nits have hatched and can be targeted.
- Special circumstances:
Infants under 6 months – use a prescription‑only, low‑toxicity product and repeat after 7 days.
Resistant infestations – consider a different class of pediculicide for the second round, still observing the 7‑day interval.
Severe outbreaks – a third application at day 14 may be warranted, especially if live lice are still detected after the second treatment.
Verification before re‑treatment: Examine the scalp and hair under bright light. If live lice are observed, treat immediately regardless of the schedule. If only empty shells remain, wait until the next scheduled interval.
Key points to remember:
- The repeat must occur after the majority of eggs have hatched.
- The interval should not be shorter than 5 days, to avoid unnecessary chemical exposure, nor longer than 10 days, to prevent a new generation of eggs from reproducing.
- Consistent combing with a fine‑toothed nit comb after each application enhances success and reduces the need for additional chemical doses.