How long does it take for lice to grow? - briefly
Lice progress from eggs to reproductive adults in roughly 7–10 days under typical indoor conditions. Warmer temperatures can shorten this cycle to about 5 days.
How long does it take for lice to grow? - in detail
Lice develop through a predictable sequence of stages that can be measured in days. The cycle begins with the egg, commonly called a nit, which is attached firmly to hair shafts. Under normal indoor temperatures (approximately 22‑25 °C or 72‑77 °F) a nit requires 7–10 days to hatch. The emerging nymph is a miniature adult and must undergo three successive molts before reaching full maturity. Each molt takes roughly 2–3 days, so the nymphal period lasts about 9–12 days in total.
After the final molt, the adult louse is capable of reproduction. Female head lice start laying eggs after about 2 days of mating, and they deposit roughly 3–5 eggs per day. The adult lifespan ranges from 30 to 40 days, during which a single female can produce up to 100 eggs. Body lice follow a similar timetable, with hatching at 6–8 days and maturation completed in 10–12 days; their adult phase may extend to 30 days under favorable conditions.
Environmental factors influence the speed of development. Higher ambient temperatures (up to 30 °C or 86 °F) accelerate egg hatching and nymphal growth, potentially reducing the total cycle by 1–2 days. Conversely, temperatures below 15 °C (59 °F) slow progression, extending the hatching period beyond 12 days and lengthening each molt.
In summary, from egg deposition to the emergence of a reproductive adult, the process typically spans 14–21 days, with the entire lifespan of an individual louse lasting about one month. This timeline applies to the most common human lice species when conditions are optimal.