How long do lice live away from the head? - briefly
Adult head lice can survive away from a human scalp for roughly 24–48 hours, with survival extending slightly under warm, humid conditions; nymphs typically die within a day without a host.
How long do lice live away from the head? - in detail
Lice survive only a short period once they are separated from a human host. An adult head louse can live without a blood meal for approximately 24 hours at room temperature (20‑25 °C) and moderate humidity (40‑60 %). Under cooler, drier conditions the survival time drops to 12 hours or less, while a warm, moist environment can extend it to about 48 hours.
Nymphs, which are smaller and have less stored energy, die slightly faster, typically within 12‑24 hours under the same conditions.
Eggs (nits) are not capable of hatching off the scalp because they require the constant temperature and humidity provided by a host’s head. They remain viable for up to 7‑10 days, but will not develop unless they are transferred to a suitable environment.
Key factors influencing off‑host longevity:
- Temperature: Below 15 °C accelerates dehydration; above 45 °C causes rapid mortality.
- Relative humidity: Below 30 % leads to desiccation within hours; 50‑70 % prolongs survival up to two days.
- Air flow: Increased ventilation speeds moisture loss, reducing lifespan.
- Food source: Absence of blood eliminates the ability to sustain metabolic functions.
In practical terms, lice on clothing, bedding, or personal items are unlikely to remain viable beyond two days, and most will die within one day if conditions are unfavorable. Effective control therefore focuses on treating the host and washing or isolating personal items for at least 48 hours to ensure any stray insects have perished.