How do lice reproduce and spread? - briefly
Lice females lay 6‑10 eggs (nits) on each hair shaft daily, and the eggs hatch in about 7‑10 days, producing nymphs that mature in another week. Spread occurs primarily through direct head‑to‑head contact or sharing items such as combs, hats, and bedding.
How do lice reproduce and spread? - in detail
Lice are obligate ectoparasites that complete their entire life cycle on a human host. The three species most relevant to humans are head lice, body lice and pubic lice, each adapted to a specific body region.
Female lice deposit oval eggs, commonly called nits, on individual hairs or clothing fibers. Each female can lay 5‑10 eggs per day, attaching them with a cement‑like secretion that hardens within minutes. The eggs hatch after 7‑10 days, depending on temperature and humidity.
The emerging nymph passes through three successive molts. Each instar lasts 2‑3 days, after which the insect enlarges and produces a new exoskeleton. Full sexual maturity is reached in 9‑12 days from egg deposition, at which point the adult can reproduce. Under optimal conditions a single female can generate 10‑12 clutches during a lifespan of 30‑40 days, resulting in rapid population growth.
Transmission occurs primarily through direct physical contact. Head‑to‑head contact enables nits and mobile insects to move from one scalp to another. Indirect spread involves sharing personal items such as combs, hats, scarves or bedding, which may retain viable eggs for several days. Body lice are transmitted via contaminated clothing; infestation arises when lice migrate from a contaminated garment to the skin. Pubic lice spread through sexual contact and, less commonly, through sharing towels or bedding.
Factors that accelerate dissemination include high population density, limited access to laundering facilities, warm and humid environments, and the presence of resistant lice strains. Effective control relies on removing nits, treating all infested individuals simultaneously, and maintaining clean clothing and personal items.