Where do lice live and where do they come from? - briefly
Lice inhabit the hair, scalp, or feathers of their specific hosts—humans, birds, or other mammals—staying close to the skin to feed on blood. They arise from eggs (nits) deposited by adult females on the host, which hatch into nymphs that remain on the same organism for their entire life cycle.
Where do lice live and where do they come from? - in detail
Lice are obligate ectoparasites that survive exclusively on warm‑blooded hosts. Their entire life cycle—egg, nymph, adult—occurs on the host’s body or on items that remain in close contact with it. Human lice are divided into three species, each occupying a distinct ecological niche:
- Head lice (Pediculus humanus capitis) – reside on the scalp, attaching to hair shafts near the neck and behind the ears. They lay eggs (nits) firmly against the hair shaft, where they remain protected until hatching.
- Body lice (Pediculus humanus corporis) – live in the seams of clothing, especially undergarments and socks. They move to the skin only to feed, then return to the fabric to lay eggs. Infestations appear when clothing is infrequently changed or washed.
- Pubic lice (Pthirus pubis) – inhabit the coarse hair of the genital region, perianal area, and occasionally chest or facial hair. Eggs are attached to hair shafts close to the skin surface.
Lice are not capable of surviving away from a host for more than a day; they require a stable temperature of 30–34 °C and a constant supply of blood. Environmental reservoirs such as bedding, hats, combs, or upholstered furniture can harbor nits, but adult insects die quickly without direct contact with a living host.
The origin of lice infestations can be traced to three primary pathways:
- Direct person‑to‑person contact – the most common route for head and pubic lice, transferred through head‑to‑head or sexual contact.
- Indirect transmission via personal items – body lice spread through shared clothing, towels, or bedding that have not been laundered at temperatures above 50 °C.
- Zoonotic transfer – some lice species originally parasitized other mammals; however, human lice have co‑evolved with their hosts for millions of years, resulting in strict host specificity.
Genetic studies indicate that head lice diverged from body lice approximately 100,000 years ago, reflecting adaptation to different human behaviors such as clothing use. Pubic lice likely originated from a separate lineage that colonized humans after the emergence of pubic hair.
Effective control relies on eliminating the host environment that supports the parasite: regular washing of clothing and bedding at high temperature, thorough combing of hair to remove nits, and, where appropriate, topical insecticides applied to the affected area. Continuous removal of eggs and avoidance of re‑exposure prevent re‑infestation.