How long does a lice infestation last? - briefly
Without treatment, head lice usually persist for about four weeks, as adult insects live 3–4 weeks and their eggs hatch within a week. Effective treatment can eliminate the problem in 5–7 days.
How long does a lice infestation last? - in detail
A head‑lice outbreak typically persists until the entire population of insects and their eggs are eliminated. The life cycle of Pediculus humanus capitis lasts about 7–10 days: eggs (nits) hatch in 7–9 days, nymphs mature to adults in 4–6 days, and adult lice live up to 30 days, laying 5–10 eggs per day. Because eggs are resistant to most insecticides, treatment must continue for at least two weeks after the first application to cover the period when newly hatched nymphs become vulnerable.
Effective eradication follows a schedule:
- Day 0: apply a recommended pediculicide or use a thorough wet‑comb method.
- Day 7–10: repeat treatment to kill lice that emerged from surviving eggs.
- Day 14–21: perform a final check and retreat if any live lice or viable nits remain.
If the above regimen is followed without re‑exposure, the infestation usually resolves within 2–3 weeks. Failure to repeat treatment, incomplete nit removal, or continued contact with infested individuals can extend the problem indefinitely, leading to chronic reinfestation cycles.
Factors that influence duration include:
- Resistance of lice to the chosen product.
- Thoroughness of nit removal during combing.
- Frequency of close contact with untreated hosts.
- Adherence to the treatment timeline.
Monitoring should continue for at least one month after the last treatment to confirm the absence of live insects and to prevent resurgence.