How quickly are lice transmitted? - briefly
Lice are transferred almost instantly during direct head‑to‑head contact, often after a single brief encounter. Because nits hatch in about 7–10 days, a noticeable infestation can develop within a week of exposure.
How quickly are lice transmitted? - in detail
Lice move from one person to another the moment a live insect makes physical contact with a new host. Direct head‑to‑head contact can transfer an adult or a mobile nymph within seconds, because the insects crawl actively and do not require a feeding interval before attachment. Indirect transfer through personal items (combs, hats, pillowcases) takes longer; a viable egg must first hatch, which occurs after 7–10 days, and the emerging nymph must reach the mobile stage (approximately 3 days) before it can crawl onto another person.
Key factors that determine the overall speed of spread include:
- Life‑stage of the insect – adults and mobile nymphs can transfer instantly; eggs remain immobile.
- Duration of contact – brief head‑to‑head interaction (as little as a few seconds) is sufficient for transmission.
- Environmental conditions – temperature around 30 °C accelerates egg development and nymph maturation, shortening the window before a new host can be infected.
- Host hygiene and crowding – densely populated settings (schools, camps) increase the frequency of contacts, thereby raising transmission rates.
Once an adult lice establishes on a new host, it begins feeding within minutes and can lay eggs after 2–3 days of attachment. The first generation of offspring becomes capable of moving to other hosts roughly 9–12 days after the initial infestation, creating a rapid cycle of spread if uninterrupted. Consequently, a single infestation can generate new cases within a week, and secondary infestations may appear within two weeks under typical conditions.