How are lice born on the head? - briefly
Female lice deposit eggs on hair shafts; these nits incubate for about a week before hatching into nymphs that mature into adults. The entire cycle repeats without any external fertilization occurring on the scalp.
How are lice born on the head? - in detail
Head lice (Pediculus humanus capitis) establish a population on a human scalp through a predictable biological cycle. Adult females lay eggs (nits) on hair shafts close to the skin, where temperature and humidity favor embryonic development. Each female can deposit 5–8 eggs per day for up to three weeks, resulting in a clutch of 30–100 nits over her lifespan.
The eggs require approximately 7–10 days to hatch, depending on ambient conditions. Upon emergence, the newly born nymphs—first‑instar larvae—remain on the hair and begin feeding on blood within hours. Nymphs undergo three successive molts, each lasting 2–3 days, before reaching adulthood. The complete maturation from egg to adult therefore takes about 10–14 days.
Reproduction resumes once adults emerge. Mating occurs shortly after the final molt, and fertilized females immediately start oviposition. Because the entire cycle can be completed in less than three weeks, a small initial infestation can expand rapidly if unchecked.
Transmission to a new host occurs primarily through direct head‑to‑head contact, which transfers live lice or eggs. Indirect transfer via personal items (combs, hats, scarves) is possible but less common, as nits require a warm, moist environment to survive. Eggs attached to hair shafts can remain viable for up to 10 days away from a host; however, adult lice die within 1–2 days without a blood meal.
Key points of the life cycle:
- Egg deposition: 5–8 eggs/day, attached within 1 mm of scalp.
- Incubation: 7–10 days.
- Nymphal stages: three molts, each 2–3 days.
- Adult lifespan: 30–45 days with continuous feeding.
- Reproductive output: up to 100 eggs per female.
- Transmission: direct head contact; limited indirect via fomites.
Understanding each stage clarifies how an initial introduction of a few lice can develop into a noticeable infestation within a month. Effective control measures target the early stages—removing nits and eliminating live lice before they reproduce.