How long does it take for lice to hatch on the head? - briefly
Eggs (nits) on a human scalp typically hatch within 7–10 days. Slight variations may occur due to temperature and hair conditions.
How long does it take for lice to hatch on the head? - in detail
The incubation period for head‑lice eggs attached to a human scalp averages 7 to 10 days under normal conditions. Temperature is the primary factor: at skin temperature (approximately 33–35 °C or 91–95 °F) development proceeds at the fastest rate. Cooler environments slow embryogenesis, extending the hatch time by several days.
Typical timeline:
- Day 0: Female deposits an egg (nit) and secures it to a hair shaft with cement.
- Days 1‑3: Embryo undergoes cleavage; the egg appears opaque.
- Days 4‑6: Organogenesis progresses; the egg becomes slightly more translucent.
- Days 7‑10: Nymph emerges, leaving the eggshell attached to the hair.
Variations:
- Ambient temperature: Below 30 °C (86 °F) can lengthen the period to 12‑14 days; above 37 °C (99 °F) may reduce it to 6‑7 days.
- Host hygiene: Frequent washing does not affect the internal development but can remove some eggs before they hatch.
- Egg age at detection: Newly laid eggs hatch earlier than those that have been on the scalp for several days.
After hatching, a nymph requires about 5‑7 days of feeding before it molts into an adult. Understanding this schedule is essential for timing treatment applications to eliminate both existing lice and newly emerged nymphs.