How do lice form on a human head? - briefly
Lice appear on a scalp when a fertilized female deposits eggs (nits) that hatch into nymphs, which feed on blood and develop into adults within about a week.
How do lice form on a human head? - in detail
Lice infestations begin when a female adult deposits her eggs, called nits, on hair shafts close to the scalp. The adhesive secretions harden, securing the eggs for the 7‑9‑day incubation period. Upon hatching, nymphs emerge, resembling miniature adults and immediately begin feeding on blood. They mature through three successive molts over approximately 9‑12 days, after which they become capable of reproduction.
Transmission occurs primarily through direct head‑to‑head contact, which transfers mobile nymphs and adults. Indirect transfer is possible when hair accessories, hats, or bedding retain viable lice or nits; the insects survive up to 48 hours off the host under favorable temperature (20‑30 °C) and humidity (>50 %). A single fertilized female can lay 5‑10 eggs per day, producing up to 100 eggs during her 30‑day lifespan, rapidly expanding the population.
Key factors that facilitate colonization include:
- Warm, moist scalp environment that supports feeding and development.
- Dense hair that provides shelter and reduces detection.
- Close proximity to other infested individuals, especially in schools or group settings.
- Lack of regular hair hygiene practices, which does not prevent infestation but may delay detection.
The life cycle completes in about three weeks, after which the cycle repeats if new eggs are not removed. Effective control requires eliminating live lice and all viable nits, typically through combing with a fine‑toothed lice comb and applying an appropriate pediculicide that targets both stages. Regular inspection of the scalp and hair, combined with cleaning of personal items, interrupts transmission and prevents re‑infestation.