How quickly do lice appear after infection? - briefly
Eggs typically hatch in 7–10 days, and the newly emerged nymphs mature to mobile adults within a few additional days, making lice generally observable by the end of the second week after exposure.
How quickly do lice appear after infection? - in detail
Lice become detectable within a predictable timeframe after a person acquires them. Female lice lay eggs (nits) near the scalp base; each egg hatches in 7–10 days under optimal temperature (30–32 °C) and humidity. Newly emerged nymphs require an additional 5–7 days of feeding before reaching adult size and mobility. Consequently, the first visible signs—itching, live lice, or empty shells—typically appear between 10 and 14 days after the initial contact with an infested individual.
The progression can be summarized:
- Egg deposition: 1–2 days after the adult female attaches.
- Incubation: 7–10 days for egg to hatch.
- Nymph development: 5–7 days of successive molts.
- Adult emergence: 12–14 days post‑contact; at this stage, reproduction begins, accelerating population growth.
Factors influencing this schedule include:
- Host temperature: Cooler scalp conditions extend incubation by 1–2 days.
- Hair length and density: Longer, denser hair provides more attachment sites, potentially shortening the nymph maturation period.
- Environmental humidity: Low humidity can delay egg hatching, while high humidity accelerates it.
- Species variation: Pediculus humanus capitis (head lice) follows the timeline above; body lice (Pediculus humanus corporis) may hatch slightly faster due to warmer clothing environments.
Early detection relies on visual inspection of the hair shaft for live insects or empty nits within the first two weeks. Prompt treatment at this stage prevents the exponential increase that occurs after the adult population establishes itself.