How many days does the lice life cycle last? - briefly
The full development of a head louse, from egg through nymph stages to adult, typically requires about three weeks (≈ 21–24 days) under normal conditions. Higher temperatures can lengthen the cycle to roughly 30 days.
How many days does the lice life cycle last? - in detail
The life cycle of a human louse proceeds through three distinct phases: egg, nymph, and adult.
Eggs, commonly called nits, are attached to hair shafts near the scalp. Under optimal conditions (temperature around 30 °C and adequate humidity), embryonic development requires 7–10 days before hatching.
Nymphs emerge as tiny, mobile insects. They undergo three successive molts, each lasting approximately 3–4 days. Consequently, the nymphal period spans roughly 9–12 days. During this time, the insects feed frequently on blood, gaining the size and physiological maturity needed for reproduction.
Adult lice become capable of laying eggs after reaching sexual maturity, which occurs about 2–3 days post‑final molt. An adult female can produce 4–6 eggs per day, continuing for about 30 days before dying. The average adult lifespan, from emergence to death, is 30–35 days, though some individuals survive up to 45 days under favorable circumstances.
Summing the stages yields a total cycle length of approximately 30–40 days from egg deposition to the death of the originating adult. Variations arise among species: head lice (Pediculus humanus capitis) follow the timeline described above; body lice (Pediculus humanus corporis) exhibit a slightly longer egg incubation (8–12 days) and adult longevity (up to 50 days). Pubic lice (Pthirus pubis) have comparable durations, with eggs hatching in 7–10 days and adults living 30–40 days.
Environmental factors such as temperature, humidity, and host grooming habits can accelerate or retard development. Higher temperatures shorten incubation, while low humidity may increase egg mortality. Regular removal of nits and use of pediculicidal treatments interrupt the cycle, preventing the emergence of new adults.