How long do lice survive outside a host? - briefly
Adult head lice remain viable for roughly 24 hours when separated from a person, extending to 48 hours only under warm, humid conditions. In dry or cooler environments, survival drops to a few hours.
How long do lice survive outside a host? - in detail
Lice can remain viable after leaving a human host, but survival is limited by environmental factors. Temperature, relative humidity, and the type of surface determine the length of time the insects stay alive.
- At moderate temperatures (20‑30 °C) with high humidity (≥70 %), head lice may survive up to 48 hours. Under the same conditions, body lice can persist slightly longer, reaching 72 hours.
- In dry environments (humidity ≤40 %) or at temperatures above 35 °C, mortality occurs within 6‑12 hours for all species.
- Cold conditions (4‑10 °C) extend viability; head lice may live for 5‑7 days, while body lice can endure up to 10 days. Freezing temperatures (<0 °C) cause rapid death, usually within 30 minutes.
- On smooth, non‑porous surfaces such as plastic or metal, lice lose moisture faster, reducing survival to 12‑24 hours even under favorable humidity. Porous materials like clothing or bedding retain moisture, allowing the insects to remain alive for the maximum periods noted above.
Eggs (nits) are more resistant. When detached from the host, they can remain viable for several weeks if kept in a humid environment, but hatchability drops sharply after 10‑14 days under dry conditions.
In practical terms, the risk of transmission diminishes sharply after 24 hours on most household surfaces, especially when ambient humidity is low. Effective decontamination—washing fabrics at ≥60 °C or using a dryer on high heat—eliminates both adult lice and viable eggs. Vacuuming and thorough cleaning of surfaces further reduce the already limited survival window.