How long until lice die? - briefly
Without a host, adult head lice survive only 24–48 hours; on a human scalp they live up to 7–10 days before dying naturally. Their eggs (nits) hatch in about 7 days, after which the newly emerged lice follow the same lifespan limits.
How long until lice die? - in detail
Lice survive on a human scalp for about three weeks. An adult female lays 5–10 eggs each day; the eggs hatch after 7–10 days, and the newly emerged nymph matures in another 7–10 days. Consequently, a complete life cycle—from egg to reproducing adult—takes roughly three weeks. Once an adult leaves the host, it can live only 1–2 days before dehydration kills it.
External conditions that accelerate death include:
- Temperature: exposure to ≥130 °F (54 °C) for 5 minutes or immersion in water at ≥140 °F (60 °C) for 10 minutes destroys both lice and nits. Freezing at ≤‑5 °F (‑20 °C) for 48 hours also proves lethal.
- Desiccation: low‑humidity environments (<30 % relative humidity) cause rapid dehydration, killing lice within hours.
- Chemical agents: pediculicidal shampoos and lotions containing permethrin, pyrethrin, or dimethicone act within 10–30 minutes, killing most insects on contact. Resistance can extend survival, requiring a second treatment 7–10 days later to eliminate newly hatched nymphs.
- Mechanical removal: combing with a fine‑toothed lice comb removes live insects and eggs, reducing the population within a few days when performed twice daily for a week.
In household items, laundering at ≥130 °F or dry‑cleaning eliminates infestations. Sealing non‑washable objects in airtight bags for two weeks prevents hatching, because eggs cannot survive without a host beyond that period.
Overall, without intervention, adult lice persist for roughly 20–30 days on a person, die within 48 hours when removed from a host, and can be eradicated in a controlled environment within hours to days depending on temperature, humidity, and treatment method.