How many days do lice live on the head? - briefly
Head lice usually survive about 30 days on a human scalp, with some individuals lasting up to 45 days under optimal conditions. Their lifespan is limited by the need for blood meals and the host’s grooming habits.
How many days do lice live on the head? - in detail
Lice survive on a human scalp for a limited period that depends on their developmental stage, environmental conditions, and host hygiene.
Adult head‑lice (Pediculus humanus capitis) can live up to 30 days if they have continuous access to blood. Their lifespan shortens when temperature drops below 20 °C or when the host’s scalp becomes dry, because dehydration reduces feeding efficiency.
Nymphs, which hatch from eggs after about 7–10 days, progress through three molts. Each instar lasts roughly 3–5 days, after which the insect reaches adulthood. Consequently, a newly emerged nymph can survive for approximately 18–23 days before death, assuming it successfully molts each time.
Eggs (nits) remain viable for 7–10 days before hatching. If the egg is not hatched, it will eventually die and fall off the hair shaft.
Key factors influencing survival time:
- Temperature: optimal range 28–32 °C; lower temperatures accelerate mortality.
- Humidity: relative humidity above 50 % sustains activity; dry conditions increase desiccation risk.
- Blood supply: uninterrupted feeding is essential; prolonged periods without a host lead to death within 2–3 days.
- Chemical exposure: insecticidal treatments or frequent shampooing can reduce lifespan dramatically, often killing adults within hours.
Overall, an adult louse can remain alive on a head for about one month under ideal conditions, while immature stages survive for less than three weeks. Eggs persist for up to ten days before either hatching or becoming non‑viable.