How do lice appear on a human's head? - briefly
Lice infest a scalp primarily through direct head‑to‑head contact or by sharing contaminated items such as hats, combs, or hair accessories. Female lice lay eggs (nits) on hair shafts, which hatch within a week, establishing a new population on the host.
How do lice appear on a human's head? - in detail
Lice infestations begin when adult female head‑lice (Pediculus humanus capitis) transfers from an infested individual to a new host. Transfer occurs primarily through direct head‑to‑head contact; brief physical interactions such as hugging, sharing helmets, or close proximity in crowded environments provide the necessary bridge for the insect to crawl onto a clean scalp. Indirect transmission via personal items—combs, brushes, hats, pillowcases, or upholstered furniture—can also occur when lice or their eggs (nits) survive on these surfaces for several days.
Once on a new host, the female lays 5–10 eggs per day, attaching each nit to a hair shaft about 1 mm from the scalp. Eggs hatch after 7–10 days, releasing mobile nymphs that resemble miniature adults. Nymphs undergo three molts over a period of 9–12 days before reaching reproductive maturity. The entire life cycle, from egg to egg‑laying adult, spans approximately 3 weeks under optimal temperature (30 °C) and humidity conditions.
Key factors that facilitate colonisation include:
- Warm, moist environment near the scalp, which enhances egg viability and nymph development.
- Dense hair providing shelter and a stable substrate for attachment.
- Frequent close contact among individuals, especially in schools, daycare centers, and sports teams.
Control measures target each stage of the cycle: mechanical removal of nits with fine‑toothed combs, topical insecticides that kill live lice, and environmental decontamination of personal items through washing at ≥ 60 °C or sealing in plastic bags for two weeks to prevent hatching. Regular inspection of the hair and scalp, particularly after known exposure, remains the most effective method for early detection and interruption of transmission.