How long do lice live when not on hair? - briefly
Without a host, lice survive roughly one to two days before dying from dehydration and lack of nutrition.
How long do lice live when not on hair? - in detail
Lice can survive only a limited time without a human host because they require constant blood meals and a warm, humid environment. Adult head lice typically endure 24–48 hours when removed from hair. Nymphs, which are smaller and less mobile, survive roughly 12–24 hours under the same conditions. Eggs (nits) are more resilient; they may remain viable for up to a week if the temperature stays around 25–30 °C (77–86 °F) and humidity exceeds 50 %. However, once the embryo has hatched, the emerging nymph follows the adult’s short survival window.
Key factors influencing off‑host longevity:
- Temperature: Below 20 °C (68 °F) metabolic activity slows, extending survival to about 48 hours for adults, but extreme heat above 35 °C (95 °F) can be lethal within a few hours.
- Humidity: Low humidity (under 30 %) causes rapid dehydration, reducing survival to less than 12 hours; high humidity (above 70 %) can prolong life by several hours.
- Substrate: Lice cling to fabrics, pillowcases, or furniture. Smooth, non‑absorbing surfaces accelerate desiccation, whereas porous materials retain moisture longer.
- Species: Body lice (Pediculus humanus humanus) are slightly more tolerant of off‑host conditions, surviving up to 72 hours, while crab lice (Pthirus pubis) have similar limits to head lice.
In practical terms, any environment lacking a host for more than two days will likely be inhospitable to live lice, though dormant eggs may remain capable of hatching if later exposed to suitable conditions. Regular laundering of bedding and clothing at temperatures above 60 °C (140 °F) eliminates both viable insects and eggs, effectively breaking the life cycle.