How long do louse eggs survive outside a human body? - briefly
Louse eggs, referred to as «nits», stay viable for roughly 3–7 days after leaving a host. Higher temperatures and lower humidity reduce this survival period.
How long do louse eggs survive outside a human body? - in detail
Louse eggs, commonly called nits, remain viable only while conditions prevent desiccation and extreme temperatures. Under typical indoor humidity (40‑60 % relative humidity) and ambient temperature (20‑25 °C), eggs can persist for up to 48 hours before embryonic development ceases. Lower humidity accelerates drying, reducing survival to 12‑24 hours. Elevated temperatures above 35 °C denature proteins, shortening viability to a few hours; exposure to freezing temperatures (< 0 °C) also compromises embryonic cells within a similar timeframe.
Key environmental factors influencing external egg survival:
- Humidity: ≥ 30 % maintains moisture; below this threshold, eggs desiccate rapidly.
- Temperature: 20‑30 °C optimal; > 35 °C or < 5 °C detrimental.
- Substrate: Smooth surfaces (e.g., hair, fabric) protect against mechanical removal; porous materials expose eggs to airflow, increasing loss of moisture.
- Light: Direct sunlight accelerates drying and heat buildup, decreasing lifespan.
Practical implications for control:
- Immediate removal of clothing and bedding, followed by laundering at ≥ 60 °C, eliminates residual eggs.
- Dry cleaning or exposure to high‑heat dryer cycles for at least 30 minutes ensures non‑viability.
- Vacuuming and discarding infested items reduce the risk of re‑infestation, as eggs surviving beyond 48 hours are unlikely to hatch.
Overall, external louse eggs survive no longer than two days under favorable indoor conditions, with survival sharply decreasing as humidity drops or temperature rises beyond optimal ranges.