How long do head lice live on the head? - briefly
Adult head lice can remain alive on a human scalp for roughly 30 days before dying without a blood meal. Nymphs develop into maturity within 7‑10 days, allowing the infestation to persist for up to a month.
How long do head lice live on the head? - in detail
Adult head lice survive on the human scalp for approximately 30 days under optimal conditions. During this period an adult can lay up to 10 eggs per day, contributing to rapid population growth.
The complete life cycle comprises three stages:
- Egg (nit): deposited near the hair shaft base, hatches in 7–10 days.
- Nymph: undergoes three molts over 9–12 days, each molt lasting about 3 days.
- Adult: emerges after the final molt, lives up to 30 days while feeding on blood.
Environmental factors affect longevity. Temperatures between 28 °C and 32 °C and constant access to blood prolong survival; temperatures above 40 °C or below 15 °C accelerate mortality. Regular combing or chemical treatment reduces available feeding sites, shortening the adult phase.
Off‑host survival is limited. Lice can endure without a host for 24–48 hours, with a maximum of 72 hours under cool, humid conditions. Depriving them of a blood source beyond this window leads to death.
Effective control relies on timing interventions to interrupt the cycle before the nymph stage matures. Re‑treatment after 7–10 days targets newly hatched nits, while a final application around day 14 ensures elimination of any surviving adults.