How long do lice and nits survive outside a human body? - briefly
Adult head lice can live 24–48 hours without a human host, while nits remain viable for roughly 7–10 days if kept in a warm, humid environment.
How long do lice and nits survive outside a human body? - in detail
Adult head lice can remain viable for only a short period once separated from a human scalp. Under ambient indoor temperatures (20‑25 °C) and relative humidity above 50 %, they survive up to 24 hours; lower humidity reduces this to 6‑12 hours, and temperatures above 35 °C cause death within minutes. On dry, cool surfaces such as clothing or furniture, survival rarely exceeds 2 days. Body lice, which inhabit clothing rather than hair, show a similar off‑host lifespan, typically 24‑48 hours under comparable conditions.
Nits (lice eggs) are more resistant to desiccation. When attached to hair shafts they remain viable for 7‑10 days, because the protective shell retains moisture. Detached nits can persist longer on fabrics or in litter if humidity stays above 40 % and temperature remains between 15‑30 °C; laboratory studies report hatchability after 10‑14 days under optimal conditions. In dry, warm environments (relative humidity <30 %, temperature >30 °C) hatch rates drop sharply, and most eggs become non‑viable within 4‑5 days.
Key factors influencing off‑host survival:
- Temperature: 20‑30 °C favors longevity; >35 °C accelerates mortality.
- Relative humidity: >50 % prolongs life; <30 % shortens it markedly.
- Surface type: Porous fabrics retain moisture, extending nits’ viability; smooth, dry surfaces hasten adult death.
- Exposure to sunlight: UV radiation reduces survival of both stages within hours.
Practical implications for control:
- Items that may have contacted infested hair (combs, hats, pillowcases) should be laundered in hot water (≥60 °C) and dried on high heat; this eliminates both adults and eggs.
- Non‑washable objects can be sealed in a plastic bag for at least 48 hours; the lack of moisture will kill adult lice, while most nits will lose viability.
- Vacuuming carpets and upholstery removes detached nits; the mechanical action and low humidity in vacuum bags further diminish hatch potential.
In summary, adult lice survive off‑host for less than two days under typical indoor conditions, whereas nits can remain viable for up to two weeks if protected by moisture and moderate temperature. Environmental control measures that reduce humidity and increase temperature effectively limit the risk of re‑infestation from contaminated items.