What is a head louse? - briefly
A head louse is a tiny, wingless insect (Pediculus humanus capitis) that inhabits the human scalp, feeding on blood and attaching its eggs, called nits, to hair shafts. Infestation produces itching and can be eliminated with topical pediculicides or by manually removing the insects and their eggs.
What is a head louse? - in detail
A head louse (Pediculus humanus capitis) is a small, wing‑less, obligate ectoparasite that lives on the human scalp and feeds on blood. Adult insects measure 2–4 mm, have a flattened body, six legs equipped with claws for gripping hair shafts, and a mouthpart designed for piercing skin.
The organism’s development proceeds through three distinct stages: egg (nit), nymph, and adult. Eggs are cemented to the base of hair strands and hatch after 7–10 days. Nymphs undergo three molts over 9–12 days before reaching maturity. An adult female can lay 6–10 eggs per day, producing up to 100 eggs in her lifetime.
Transmission occurs primarily by direct head‑to‑head contact, allowing mobile lice to move between hosts. Indirect spread via personal items (combs, hats, bedding) is less common because lice cannot survive long off a human body.
Infestation signs include persistent itching caused by an allergic reaction to saliva, the presence of live insects or nits near the scalp, and secondary skin lesions from scratching. Diagnosis relies on visual inspection of hair for live lice and firmly attached, oval nits within 1 cm of the scalp.
Effective management combines chemical and mechanical methods. Commonly used pediculicides contain dimethicone, pyrethrins, or ivermectin; resistance to older agents (e.g., permethrin) is documented. Mechanical removal involves fine‑toothed combs applied to wet hair after a conditioning agent, repeated every 2–3 days for at least two weeks to capture newly hatched nymphs. Environmental measures include washing clothing and bedding in hot water (≥ 60 °C) or sealing them in plastic bags for 48 hours to eliminate any detached lice.
Prevention focuses on minimizing head contact in settings where infestation rates are high (schools, camps) and discouraging the sharing of personal hair accessories. Regular scalp examinations during outbreaks enable early detection and reduce spread.