How long can lice survive without a human? - briefly
Adult head lice can survive up to 48 hours without a human host. Nymphs typically endure only 24–36 hours in the same conditions.
How long can lice survive without a human? - in detail
Lice require blood meals from a human host to reproduce and maintain metabolic activity. When deprived of a host, their survival depends on life stage, temperature, and humidity.
Adult head‑lice (Pediculus humanus capitis) can persist for 24–48 hours without feeding under normal indoor conditions (20‑25 °C, 40‑60 % relative humidity). Cooler temperatures extend this period slightly, while high heat (>30 °C) accelerates dehydration and death within a few hours.
Nymphs, which have not yet reached maturity, have a shorter starvation tolerance. They typically survive 12–24 hours without a blood source, dying sooner if ambient humidity falls below 30 %.
Eggs (nits) are the most resistant stage. Encased in a protective shell, they can remain viable for up to 10 days if kept in a moist environment (≥50 % humidity). In dry air, viability declines sharply after 5 days. The eggs will not hatch without a host, but the embryo can endure several days awaiting suitable conditions.
Extreme conditions dramatically alter survival times:
- Cold: Exposure to temperatures below 5 °C can halt metabolic processes, allowing lice to survive for weeks in a dormant state, though they will not develop or reproduce.
- Heat: Temperatures above 45 °C cause rapid protein denaturation, resulting in death within minutes.
- Desiccation: Low humidity (<20 %) leads to rapid water loss, killing adults and nymphs within a few hours.
In summary, adult lice survive roughly one to two days without a human, nymphs half that time, and eggs can stay viable for up to ten days under favorable moisture levels, with extreme temperatures either prolonging dormancy or causing rapid mortality.