How long do lice live on the head? - briefly
Adult head lice typically survive about 30 days on a human scalp, during which they feed and reproduce; without a host they die within 1–2 days.
How long do lice live on the head? - in detail
Head lice survive on a human scalp for a limited period, determined by their developmental stage and access to blood. An adult female can live approximately 20–30 days while feeding regularly. She produces up to six eggs per day, which are attached to hair shafts and hatch in 7–10 days.
After hatching, the immature form—called a nymph—undergoes three molts. Each molt requires about 3 days, so the nymphal phase lasts roughly 9–12 days before the insect reaches adulthood. During this stage the lice must feed every 4–5 hours; without a blood meal they die within 24–48 hours.
If a louse is removed from the host, its survival time drops sharply. In a controlled environment, an adult can persist for only 1–2 days without a blood source, and under typical household conditions the limit is generally 48 hours.
Key points summarizing the lifecycle and survival:
- Egg (nit): 7–10 days to hatch, remains viable only while attached to hair.
- Nymph: 3 molts over 9–12 days; requires frequent blood meals.
- Adult: 20–30 days on a host, continuous feeding; up to 6 eggs per day.
- Off‑host survival: 24–48 hours for adults; eggs lose viability after 7–10 days without a host.
The overall duration that a head louse can remain on a person, from egg to death of the adult, therefore spans roughly 30–45 days, assuming uninterrupted access to blood and favorable environmental conditions. Any interruption in feeding or removal of the host reduces this timeframe dramatically.