How long until lice multiply? - briefly
A female louse lays 5–6 eggs each day, the eggs hatch in 7–10 days, and the resulting nymphs become reproductive adults after another 9–12 days. Thus, a population can double in roughly two weeks.
How long until lice multiply? - in detail
Lice reproduce rapidly. An adult female lays between five and six eggs each day after mating, usually within one to two days of becoming an adult. Eggs (nits) require seven to ten days to hatch at typical room temperatures (20‑25 °C). The emerging nymph passes through three molts over approximately five days before reaching full maturity. Consequently, a single fertilized female can generate a new generation in roughly two weeks.
The population growth follows a geometric pattern. Assuming optimal conditions and no intervention:
- Day 0 – one fertilized adult female.
- Day 7‑10 – first batch of nits hatch, producing 5‑6 nymphs.
- Day 12‑15 – those nymphs mature and begin laying eggs.
- Day 14‑21 – second generation appears, adding another 25‑30 viable lice.
Each successive cycle shortens the interval because multiple adults lay eggs simultaneously. In practice, a noticeable surge in lice numbers occurs within ten to fourteen days after the initial infestation, and the total count can double every three to four days thereafter if untreated.
Factors that influence the timeline include ambient temperature, humidity, host grooming habits, and the availability of suitable feeding sites. Higher temperatures accelerate egg development, while cooler environments prolong it. Regular combing or chemical treatment interrupts the cycle by removing nits before they hatch or killing adults before they reproduce, thereby extending the interval between generations.