How many days can lice live? - briefly
Adult head lice typically survive around 30 days while feeding on a human host; when removed from the host, they die within one to two days.
How many days can lice live? - in detail
Lice survive for a limited period that depends on species, life stage, and environmental conditions.
Adult head lice typically live about 30 days on a human host. An adult lays 6–10 eggs per day; each egg (nit) hatches after 7–10 days. The emerging nymph passes through three molts over 9–12 days before reaching adulthood. Consequently, the full cycle from egg to death spans roughly 30–40 days when a host is continuously available.
When removed from a host, lice cannot feed and their survival drops sharply. At room temperature (20‑25 °C) and moderate humidity, an adult can endure 24–48 hours without blood. Lower temperatures or very dry air reduce this window to a few hours.
Factors influencing lifespan include:
- Temperature: 25‑30 °C maximizes activity and longevity; temperatures below 10 °C accelerate mortality.
- Humidity: 40‑70 % relative humidity supports survival; dry air causes rapid desiccation.
- Host availability: Continuous access to blood prolongs adult life; interruption shortens it dramatically.
- Species differences: Body lice (Pediculus humanus corporis) may survive up to 2 weeks off‑host in clothing, while pubic lice (Pthirus pubis) generally die within 24 hours when separated from a host.
In summary, on a person, adult lice live about a month, while off‑host survival ranges from a few hours to two days, governed by temperature, humidity, and species‑specific traits.