How long do lice live in hair? - briefly
Adult head lice remain viable on a human scalp for roughly four weeks, while newly hatched nymphs mature in about a week and then live a comparable duration.
How long do lice live in hair? - in detail
Lice that inhabit the human scalp remain viable for approximately one month. An adult female lays 6‑10 eggs each day; the eggs hatch in 7‑10 days, producing nymphs that mature through three molts over another 9‑12 days. Once fully grown, an adult can survive 20‑30 days while feeding regularly on blood.
If a louse is removed from the host, it can endure 24‑48 hours without a blood meal, extending to a maximum of about five days under optimal humidity and temperature. Depriving the parasite of a blood source accelerates death, but the insect’s life expectancy on a head is governed by the feeding cycle.
Key points:
- Egg incubation: 7‑10 days
- Nymphal development: 9‑12 days total
- Adult lifespan on scalp: 20‑30 days
- Survival off‑host: up to 5 days, typically less than 48 hours without feeding
Environmental factors such as low humidity, extreme temperatures, and lack of host contact reduce survival time dramatically. Effective control therefore targets both the adult insects and the unhatched eggs before they complete the full life cycle.