How long do head lice survive without a human? - briefly
Head lice typically live only 24–48 hours away from a human host; under ideal temperature and humidity they may survive up to about two days, but they quickly die without a blood meal.
How long do head lice survive without a human? - in detail
Head lice can remain alive outside a human scalp for only a limited period. Adult insects typically survive 24 – 48 hours when deprived of a blood meal. Nymphs, which have not yet reached maturity, exhibit a similar lifespan, often dying within a day if they cannot locate a host.
Several environmental factors influence these durations:
- Temperature: At room temperature (20 °C–22 °C) survival is close to the maximum 48 hours. Cooler conditions (below 15 °C) extend viability modestly, sometimes reaching 72 hours, while higher temperatures (above 30 °C) accelerate mortality.
- Humidity: Relative humidity above 50 % supports longer survival; low humidity (under 30 %) desiccates lice rapidly, reducing lifespan to under 12 hours.
- Food source: Lice feed every 4–5 hours. Absence of blood triggers metabolic decline, leading to death after the aforementioned intervals.
Eggs (nits) cannot hatch without direct contact with a scalp. They remain viable for up to 7 days, but embryonic development halts without the warmth and carbon‑dioxide from a host, rendering the eggs non‑infectious until re‑exposed.
In practice, the risk of transmission drops sharply after 48 hours of separation from a person, provided the environment is not artificially humidified or cooled. Effective control measures therefore focus on immediate removal of infested clothing, bedding, and personal items, followed by laundering at temperatures of at least 60 °C or sealing for a week to exceed the maximum off‑host survival window.