How long after infection do lice appear on the head? - briefly
Lice eggs typically hatch within 7–10 days, and the newly emerged nymphs become noticeable on the scalp about 9–14 days after the initial infestation.
How long after infection do lice appear on the head? - in detail
Head lice (Pediculus humanus capitis) are transmitted when viable eggs (nits) or live insects move from an infested person to a new host. After a female deposits eggs on hair shafts, each egg requires about 7–10 days to develop and hatch. The newly emerged nymphs begin feeding immediately and reach full size in another 7–10 days, during which they molt three times. Consequently, visible signs of infestation typically emerge 10–14 days after the initial contact with contaminated hair.
The first observable indicator is usually itching caused by the lice’s saliva injection during feeding. Itching may appear as early as 5 days after hatching, but most individuals notice it after a week of feeding activity. In addition to pruritus, small, translucent nits can be seen attached to the base of hair strands; they become more apparent as they darken and solidify over several days.
A practical timeline:
- Day 0–2: Transfer of eggs or adult lice occurs.
- Day 3–9: Eggs incubate; no external signs.
- Day 10–12: First nymphs hatch; mild itching may start.
- Day 14–21: Population expands; itching intensifies; nits become visible.
- Day 22 onward: Full‑size lice are abundant; symptoms are pronounced.
Detection methods rely on visual inspection with a fine-tooth comb, preferably on wet hair, to capture both live lice and attached nits. Laboratory confirmation is unnecessary in most cases; the presence of live insects or viable nits confirms infestation.
Effective treatment should begin as soon as lice are identified, using a pediculicide approved for the age group or a physical removal method. Re‑inspection after 7–10 days ensures eradication of any newly hatched nymphs that survived the initial treatment. Continuous monitoring for at least three weeks prevents reinfestation, as the life cycle completes within that period.