How long do lice and nits live outside the body? - briefly
Adult lice survive only 2–3 days when removed from a host; under favorable temperature and humidity they may persist up to 5 days. Nits remain viable for about 7 days, after which the embryos typically die.
How long do lice and nits live outside the body? - in detail
Head lice (Pediculus humanus capitis) can remain viable after leaving a human host for a limited period. Under typical indoor conditions—moderate temperature (20‑25 °C) and relative humidity around 50 %—adult insects survive approximately 30 minutes to two hours. If the environment is warm (above 30 °C) and humid (above 70 %), survival may extend to 24 hours, with rare reports of up to 48 hours in optimal laboratory settings. Beyond this timeframe, dehydration and loss of energy reserves render the insects non‑functional.
The eggs, commonly called nits, are more resistant to desiccation. When detached from hair shafts, they can endure for several days. Laboratory observations indicate that nits remain viable for 5‑10 days at room temperature and moderate humidity. In cooler, drier environments the viability shortens to about three days, whereas warm, moist conditions can preserve them for up to two weeks. Viability declines sharply after hatching; unhatched eggs lose the ability to develop if not returned to a suitable host within this window.
Factors influencing external survival:
- Temperature: Higher temperatures accelerate metabolic depletion in adults; extreme heat (> 40 °C) kills both lice and nits within minutes. Low temperatures (< 10 °C) prolong survival but eventually cause mortality.
- Humidity: Relative humidity above 50 % supports longer survival for both stages; dry air causes rapid desiccation.
- Surface type: Smooth, non‑porous surfaces (plastic, metal) retain moisture longer than porous fabrics, affecting nits more than adults.
- Light exposure: Direct sunlight contributes to rapid dehydration and mortality.
Practical implications for control:
- Items that may have contacted a host (combs, hats, pillowcases) should be washed in hot water (≥ 60 °C) and dried on high heat for at least 30 minutes.
- Non‑washable objects can be sealed in a plastic bag for a minimum of 48 hours; this exceeds the maximum survival period of adult lice.
- Vacuuming carpets and upholstery reduces the chance of residual nits remaining viable.
In summary, adult head lice survive for at most two days without a host, with typical survival under an hour in ordinary indoor conditions. Nits persist longer, remaining potentially viable for up to ten days, extending to two weeks only under optimal warmth and humidity. Effective decontamination relies on temperature, moisture control, and timely removal of contaminated items.