How long do lice live on a human head? - briefly
Adult head lice generally live about 30 days on a human scalp, completing their life cycle within that period. In the absence of a blood meal, they typically die within 7 days.
How long do lice live on a human head? - in detail
Head lice (Pediculus humanus capitis) complete their entire life cycle on the host’s scalp. An adult female deposits about 6–10 eggs (nits) per day, attaching them to hair shafts near the scalp. The eggs hatch in approximately 7–10 days, releasing nymphs that resemble miniature adults. Nymphs undergo three molts, each lasting about 3–4 days, after which they become reproductive adults. Consequently, the total development period from egg to mature louse spans roughly 2–3 weeks.
Once mature, a head louse can survive for up to 30 days without a blood meal, but regular feeding on human blood is essential for reproduction and longevity. Under optimal conditions—stable temperature (≈30 °C) and humidity (≈70 % relative humidity)—an adult may live 20–30 days on the scalp. If removed from the host, survival drops dramatically, with death occurring within 1–2 days due to desiccation.
Key time frames:
- Egg incubation: 7–10 days
- Nymphal stage (three instars): 9–12 days total
- Adult lifespan on scalp: 20–30 days
- Maximum survival off‑host: 1–2 days
Understanding these intervals clarifies why infestations can persist for several weeks and underscores the importance of timely treatment to interrupt the life cycle before new eggs hatch.