How long can lice live on a human? - briefly
Adult head lice generally survive for about 30 days on a host, feeding every few hours. Nymphs mature in 7‑10 days, so the entire population on a person persists for roughly a month without intervention.
How long can lice live on a human? - in detail
Head lice (Pediculus humanus capitis) survive on a human host for a limited period because they depend on blood meals and a stable temperature range. An adult female typically lives 30 – 40 days, during which she lays 6–10 eggs each day. The lifespan of each developmental stage is as follows:
- Egg (nit): 7–10 days before hatching, provided the environment remains warm (≈30 °C) and humid.
- Nymph (three instars): Approximately 9 – 12 days; each molt requires a fresh blood meal.
- Adult: 20–30 days on the host, after which the insect dies if it cannot find a new feeding opportunity.
If a louse is removed from the scalp, it can endure up to 48 hours without a blood source before succumbing to dehydration. The maximum survival time on a person therefore does not exceed about six weeks, assuming optimal conditions for feeding and reproduction. Factors that shorten this period include low humidity, temperatures below 20 °C, and frequent head washing that disrupts the lice’s ability to feed. Conversely, warm, humid environments and infrequent grooming can extend the adult’s life toward the upper limit of the range.