How long does it take for a louse to emerge from an egg? - briefly
A louse typically hatches about 7 to 10 days after the egg is laid.
How long does it take for a louse to emerge from an egg? - in detail
The egg stage of a human head louse lasts approximately one week. Under optimal conditions—ambient temperature around 30 °C (86 °F) and moderate humidity—the embryo completes development in 7 to 10 days, after which the nymph breaks through the nit shell.
Factors that modify this period include:
- Temperature: Cooler environments (below 20 °C) can extend incubation to 12 days or more; higher temperatures accelerate hatching but may reduce viability if excessive.
- Humidity: Low humidity dries the egg, delaying emergence; high humidity maintains moisture, supporting normal development.
- Species: Body lice (Pediculus humanus corporis) exhibit a similar 7‑10 day timeframe, while crab lice (Pthirus pubis) hatch slightly faster, often within 5‑7 days.
Following emergence, the nymph undergoes three successive molts. Each molt requires about 2‑3 days, resulting in a total of 9‑12 days from hatching to reproductive adulthood. Consequently, the full life cycle—from egg deposition to a fertile adult—spans roughly 16‑22 days.
Understanding the precise timing of egg hatching informs treatment schedules. Effective pediculicide application must target both mobile lice and unhatched eggs, with a repeat dose typically administered 7‑10 days after the initial treatment to eliminate newly emerged nymphs before they reproduce.