How many days after contact do lice appear? - briefly
Eggs hatch roughly 7–10 days after contact, and the first mobile nymphs appear about 9–14 days later, marking the onset of a visible infestation.
How many days after contact do lice appear? - in detail
The period between exposure to an infested person and the first visible signs of an infestation is determined by the life cycle of the parasite. Female lice lay eggs (nits) close to the scalp or hair shaft. Under normal ambient temperatures (around 30 °C or 86 °F), an egg takes approximately 7–10 days to hatch. The emerging nymph resembles an adult but is smaller and requires several molts before reaching reproductive maturity. Each molt occurs roughly every 2–3 days, so a nymph becomes an adult within an additional 9–12 days after hatching.
Visible symptoms such as itching, irritation, or the presence of live lice usually appear after the nymphs have begun feeding, which is typically 4–6 days after hatching. Consequently, most people notice an infestation between 10 and 14 days after the initial encounter with an infested individual.
Key factors influencing this timeline include:
- Temperature: Higher temperatures accelerate egg development; colder conditions can extend the incubation period.
- Species: Head lice, body lice, and pubic lice have slightly different hatch times, but all fall within a 7–10‑day range for eggs.
- Host grooming: Frequent hair washing or combing can remove nits before they hatch, potentially delaying or preventing visible signs.
- Egg attachment: Nits firmly cemented to the hair shaft are less likely to be dislodged, leading to a more predictable hatch schedule.
In practice, if contact with a known case occurs, monitoring for live lice and nits should begin around the seventh day and continue through the second week. Early detection during this window allows prompt treatment before the population reaches its reproductive peak.