How long can lice live? - briefly
Adult head lice survive roughly 30 days on a human host, while eggs hatch in about a week and immature stages mature within another nine days. Once off a host, they die within 24–48 hours.
How long can lice live? - in detail
Lice survive for a limited period that depends on species, temperature, and access to a human host.
The head‑lice (Pediculus humanus capitis) progresses through three stages. Eggs (nits) remain attached to hair shafts for about 7–10 days before hatching. Nymphs undergo three molts; each molt lasts roughly 2–3 days, so the nymphal phase totals 6–9 days. Adult head‑lice live 30–35 days on a person, provided they can feed daily. Without a host, adults die within 1–2 days due to dehydration.
Body‑lice (Pediculus humanus corporis) follow a similar schedule, but their eggs are laid in clothing rather than on the body. Eggs hatch after 6–9 days. Nymphal development also requires 6–9 days. Adult body‑lice survive 30–40 days on a human, but they can persist up to 10 days off‑host in a warm, humid environment.
Pubic‑lice (Pthirus pubis) have a slightly longer lifecycle. Eggs hatch in 8–10 days, nymphs mature after three molts over 9–12 days, and adults live 30–45 days while feeding. Off‑host survival is limited to 1–2 days.
Key factors influencing longevity:
- Temperature: 30 °C (86 °F) maximizes survival; lower temperatures extend egg development but increase adult mortality.
- Humidity: 70 % relative humidity supports longer adult life; dry conditions accelerate dehydration.
- Host availability: Continuous blood meals are essential; interruption reduces adult lifespan dramatically.
In summary, under optimal conditions adult lice of any type survive about one month, with eggs and nymphs adding another 1–2 weeks before reaching maturity. Off‑host survival rarely exceeds a few days.