How do lice and nits appear on a child's scalp? - briefly
Lice reach a child's hair through direct head‑to‑head contact or by sharing items such as hats, combs, or bedding, after which a fertilized female lays her eggs (nits) within a millimeter of the scalp and cements them to the hair shaft. The nits hatch in 7–10 days, releasing nymphs that become adult lice after another week.
How do lice and nits appear on a child's scalp? - in detail
Lice infestations begin when an adult female head louse (Pediculus humanus capitis) transfers from one host to another. The transfer usually occurs through direct head-to-head contact, which is common during play, sports, or close caregiving. Indirect spread via personal items (combs, hats, pillows) is possible but less frequent because lice cannot survive long off a human scalp.
Once on the scalp, the adult louse attaches its claws to hair shafts near the skin and begins feeding on blood. Within 7–10 days, it lays 5–10 eggs (nits) per day, cementing each to the base of a hair shaft with a proteinaceous glue. Nits are oval, about 0.8 mm long, and adhere tightly; they cannot be removed by washing or brushing alone.
Egg development proceeds through three stages:
- Incubation (7–10 days): The embryo matures inside the shell; the nit remains firmly attached.
- Hatching: The nymph emerges, leaving the empty shell (often called a “shell” or “egg shell”) attached to the hair.
- Maturation (5–7 days): The nymph molts three times before becoming an adult capable of reproduction.
Environmental factors such as warm, humid conditions and close group settings (daycare, schools) increase the likelihood of transmission. Children with longer hair or frequent head contact are at higher risk. Early detection relies on visual inspection of the scalp and hair for live lice, moving nymphs, or viable nits within 1 mm of the scalp surface.
Effective control requires:
- Mechanical removal: Fine-toothed combs used on wet hair to extract live insects and nits.
- Chemical treatment: FDA‑approved pediculicides applied according to label instructions, followed by a second treatment 7–10 days later to eliminate newly hatched nymphs.
- Environmental hygiene: Washing bedding, hats, and personal items in hot water (≥ 50 °C) or sealing them in plastic bags for two weeks to kill any surviving lice.
Understanding each stage of the life cycle clarifies how infestations establish and persist on a child's head, enabling targeted interventions to break the cycle.