Lice on the head: how long do they live? - briefly
Adult head lice survive roughly 30 days on a human scalp, while immature stages develop in about 9–12 days, completing a full life cycle in around a month.
Lice on the head: how long do they live? - in detail
Head lice (Pediculus humanus capitis) survive on a human scalp for a limited period. An adult female lives approximately 30 days under optimal conditions; males survive slightly less, roughly 25 days. After death, the insect dies within a few hours if removed from the host.
The insect’s development proceeds through three distinct phases:
- Egg (nit) – incubates for 7–10 days before hatching.
- Nymph – undergoes three molts over 9–12 days, each stage lasting about 3 days.
- Adult – reaches reproductive maturity after the final molt and lives up to a month.
Environmental temperature strongly influences these intervals. At 30 °C (86 °F) development accelerates, reducing the egg‑to‑adult cycle to about 14 days. Cooler temperatures (below 20 °C/68 °F) extend each stage, potentially lengthening the total cycle to 25 days. Moisture levels affect egg viability; desiccation causes rapid mortality.
Reproductive capacity determines population dynamics. A single female lays 5–10 eggs daily, totaling 100–150 eggs over her lifespan. Eggs are attached firmly to hair shafts near the scalp, where temperature and humidity favor embryogenesis. Without a host, newly hatched nymphs cannot survive more than 24 hours.
Control measures must consider the life cycle. Treatments that kill only adult lice leave viable eggs, allowing resurgence within a week. Effective protocols combine a fast‑acting insecticide with a second application 7–10 days later to eliminate hatching nymphs. Regular combing with a fine‑toothed lice comb removes both live insects and nits, reducing the breeding pool.
In summary, head lice persist on a human head for roughly one month per adult, with a complete life cycle of 14–25 days depending on environmental conditions. Understanding these timelines is essential for designing timely and comprehensive eradication strategies.