How do lice live on the head? - briefly
Lice inhabit the hair shafts on the scalp, using their claws to cling and feeding several times daily on small blood meals from the skin. They reproduce by laying eggs—nits—firmly attached to each hair strand, which hatch within about a week.
How do lice live on the head? - in detail
Lice survive on the human scalp by exploiting a constant supply of blood, a stable temperature, and the protective cover of hair. Adult females lay eggs (nits) attached to the shaft of each hair, typically within 1 mm of the scalp where warmth promotes development. The glue-like cement produced by the female secures the eggs until they hatch, usually after 7–10 days.
After hatching, nymphs emerge and immediately begin feeding on capillary blood. Each nymph undergoes three molts, growing larger at each stage. The entire nymphal period lasts about 9–12 days, after which the insect reaches reproductive maturity. An adult female can produce 5–10 eggs per day, resulting in rapid population expansion if untreated.
Feeding occurs several times a day. The louse inserts its mouthparts into a superficial blood vessel, draws a small amount of blood, and then withdraws. This brief contact minimizes host detection while providing essential nutrients for growth and egg production. The insect’s body is covered with a hardened exoskeleton that reduces water loss, allowing survival in the dry environment of the scalp.
The head provides a stable microclimate: temperature remains close to 33 °C, humidity is maintained by sweat and sebum, and the hair offers shelter from mechanical disturbance. Lice lack wings and cannot survive away from a host for more than 24 hours, making direct head‑to‑head contact the primary mode of transmission.
Key aspects of the infestation:
- Egg attachment: cemented to hair shaft near scalp.
- Development timeline: egg (7–10 days) → nymph (3 molts, 9–12 days) → adult.
- Feeding frequency: multiple times daily, each session lasting seconds.
- Reproduction rate: up to 10 eggs per day per female.
- Environmental reliance: constant warmth, humidity, and protection from hair.
Understanding these biological parameters explains why lice persist on the head and how quickly an untreated case can spread. Effective control requires disrupting one or more of these factors—removing eggs, eliminating feeding opportunities, or altering the scalp environment.