How long can lice survive without a human host? - briefly
Adult head lice typically survive up to 48 hours without a human host, whereas younger nymphs endure roughly 24 hours; both stages die within a few days if they cannot feed.
How long can lice survive without a human host? - in detail
Lice require a blood meal to sustain metabolic activity; once separated from a person, they quickly exhaust internal energy reserves. Under typical indoor conditions (20‑25 °C, 40‑60 % relative humidity), adult head lice survive no more than 24 hours. If the environment is cooler (10‑15 °C) and humidity is high, survival can extend to 48 hours, because reduced metabolic rate slows depletion of stored nutrients.
Body lice exhibit a slightly longer off‑host tolerance. Laboratory observations show adult body lice remaining viable for up to 72 hours when kept at 22 °C and 70 % humidity. In colder, drier settings, mortality occurs within 12‑24 hours.
Pubic lice (Pthirus pubis) are less tolerant of desiccation. Studies report a maximum of 24 hours without a host, with survival dropping sharply after 6‑8 hours at low humidity.
Eggs (nits) are more resilient than mobile stages. A viable egg can persist for 5‑7 days on a surface if temperature remains between 20‑30 °C and humidity exceeds 50 %. However, hatching requires contact with a host; unattended eggs will eventually desiccate and fail to develop.
Key factors influencing off‑host longevity:
- Temperature: Lower temperatures reduce metabolic demand, modestly extending survival.
- Relative humidity: High humidity prevents desiccation; below 30 % humidity accelerates death.
- Species: Body lice tolerate longer periods than head or pubic lice.
- Life stage: Eggs survive longer than nymphs or adults.
In practical terms, lice removed from a person are unlikely to remain alive beyond two days, and most will die within 24 hours under ordinary household conditions. Consequently, prompt removal of infested clothing, bedding, and personal items, followed by washing at ≥60 °C or sealing in airtight containers for a week, effectively eliminates residual insects.