What are head lice in humans?

What are head lice in humans? - briefly

Head lice are tiny, wingless insects (Pediculus humanus capitis) that inhabit the human scalp and feed on blood. They cause itching and are transmitted primarily through direct head‑to‑head contact or shared personal items.

What are head lice in humans? - in detail

Head lice are obligate ectoparasites that live on the scalp and feed exclusively on human blood. The adult insect measures 2–4 mm, has a flattened body, six legs equipped with clawed tarsi for gripping hair shafts, and a translucent grayish‑brown coloration. Females lay 6–10 eggs (nits) per day, attaching them firmly to the base of hair fibers with a cement‑like secretion; each egg hatches in 7–10 days, releasing a nymph that matures through three molts before reaching adulthood in about three weeks.

The life cycle proceeds as follows:

  1. Egg (nit) – firmly attached to hair; incubation 7–10 days.
  2. Nymph – resembles a miniature adult; requires three successive molts, each lasting 2–3 days.
  3. Adult – capable of reproduction; lives up to 30 days on a host, may survive a few days off‑host.

Feeding occurs several times daily; each blood meal lasts a few minutes. Bites cause pruritus due to an allergic reaction to saliva. Persistent scratching can lead to secondary bacterial infection, inflammation, or scalp lesions. Transmission is primarily through direct head‑to‑head contact; sharing personal items such as combs, hats, or pillows can also spread infestations, though lice survive only 24–48 hours away from a human host.

Diagnosis relies on visual identification of live lice or viable nits within 1 cm of the scalp. Effective management combines mechanical removal (wet combing with a fine‑toothed lice comb) and topical pediculicides. Recommended chemical agents include 1 % permethrin or 0.5 % malathion, applied according to manufacturer instructions and repeated after 7–10 days to eradicate newly hatched nymphs. Resistance to common insecticides has been documented; alternative treatments such as dimethicone or ivermectin may be necessary.

Prevention emphasizes avoidance of head contact in settings where infestations are common (e.g., schools, camps), routine inspection of hair during outbreaks, and avoidance of sharing personal grooming tools. Environmental control measures—washing bedding and clothing in hot water (≥ 55 °C) or sealing items in plastic bags for two weeks—reduce the risk of re‑infestation.

In summary, head lice are specialized, human‑specific parasites with a rapid reproductive cycle, causing itching and potential secondary skin complications. Accurate detection, prompt treatment, and diligent hygiene practices constitute the core strategy for eliminating and preventing outbreaks.