Pediculosis is the medical term for a lice infestation. It refers to any condition where tiny parasitic insects called lice live on the human body, feed on blood, and cause itching and irritation. There are three types, each named for where the lice settle: the head, the body, or the pubic area. Head lice are by far the most common, affecting an estimated 6 to 12 million children in the United States each year, mostly between the ages of 3 and 11.
The Three Types of Pediculosis
Each type of lice infestation involves a different species that prefers a specific part of the body. They don’t jump or fly. All three types spread through close physical contact, though the circumstances of transmission differ.
Pediculosis capitis (head lice) is the form most people encounter. Head lice live on the scalp, laying their eggs (called nits) close to the base of hair shafts where warmth from the skin helps them hatch. Children in elementary school are the most commonly affected group, largely because of close head-to-head contact during play. Head lice are not a sign of poor hygiene and occur across all socioeconomic backgrounds.
Pediculosis corporis (body lice) is the only type linked to hygiene and living conditions. Body lice actually live in clothing and bedding rather than on the skin, crawling onto the body only to feed. This type primarily affects people experiencing homelessness or those living in crowded conditions without regular access to laundry facilities. Body lice are also the only type that can transmit diseases, including epidemic typhus and trench fever.
Pediculosis pubis (pubic lice) involves a distinct species sometimes called “crabs” because of their crab-like shape under magnification. These lice attach to coarse hair, most often in the pubic region but occasionally in armpit hair, chest hair, eyebrows, or eyelashes. Pubic lice spread mainly through sexual contact. Their prevalence has dropped significantly in recent decades, which some researchers attribute to increased body hair grooming.
Common Symptoms
The hallmark symptom across all types of pediculosis is itching. The itch comes from an allergic reaction to louse saliva, which the insects inject while feeding. This means itching doesn’t always start immediately. During a first infestation, it can take two to six weeks before the immune system becomes sensitized enough to react. Someone who has had lice before may start itching within a day or two of a new infestation.
With head lice, the itching concentrates behind the ears and along the nape of the neck. You might notice small red bumps on the scalp. The nits, which are oval-shaped and yellowish-white, cling firmly to individual hair strands and can be mistaken for dandruff. The key difference is that dandruff flakes off easily while nits are cemented in place and resist removal.
Body lice cause itching primarily on the torso, wherever clothing seams press against skin. Prolonged infestations can lead to thickened, darkened skin in affected areas. Pubic lice produce itching in the groin, and you may notice bluish-gray spots on the thighs or lower abdomen where the lice have been feeding.
How Lice Spread
Head lice move from person to person almost exclusively through direct head-to-head contact. Sharing hats, brushes, and headphones gets a lot of attention as a transmission route, but studies suggest this is relatively uncommon. Lice that fall off a human host survive only about 24 to 48 hours without a blood meal, and they move poorly on smooth surfaces. That said, during an active infestation, it’s still reasonable to avoid sharing personal items that contact the head.
Body lice spread through shared clothing, towels, and bedding, particularly in environments where these items aren’t washed regularly. Pubic lice spread through skin-to-skin contact during sexual activity, though in rare cases they can be transmitted through shared bedding or towels.
Pets do not carry or transmit human lice. The species that infest humans are specifically adapted to human blood and cannot survive on animals.
How Pediculosis Is Diagnosed
Diagnosis usually comes down to finding live lice or viable nits. For head lice, the most effective method is wet combing: applying conditioner to damp hair, then systematically pulling a fine-toothed nit comb from the scalp to the ends of the hair, section by section. This is more reliable than visual inspection alone, since adult lice are only about the size of a sesame seed and move quickly away from light.
Finding nits within a quarter inch of the scalp suggests an active infestation, since eggs hatch in about 7 to 10 days and are laid close to the skin. Nits found farther along the hair shaft are typically old, already-hatched casings and don’t necessarily mean active lice are present.
Treatment Options
Head lice treatment typically starts with over-the-counter medicated shampoos or lotions that kill lice on contact. These products are applied to dry or damp hair, left on for a specified time, then rinsed out. Most require a second treatment about 9 days later to kill any lice that hatched from surviving eggs after the first application. If over-the-counter options don’t work, prescription treatments are available that use different mechanisms to kill lice, including some that suffocate them by blocking their ability to manage water.
Manual nit removal with a fine-toothed comb is an important part of treatment regardless of which product you use. Combing every two to three days for about two weeks after treatment helps catch any lice that survived. Some people opt for combing alone without any chemical treatment, which can be effective but requires diligence and patience, particularly with longer or thicker hair.
For household cleaning during a head lice episode, washing bedding and recently worn clothing in hot water (at least 130°F) and drying on high heat kills lice and nits. Items that can’t be washed can be sealed in a plastic bag for two weeks, which outlasts the lice life cycle. Vacuuming furniture and carpets is a reasonable precaution, but fumigating the house or discarding furniture is unnecessary.
Body lice treatment is simpler: improving hygiene and laundering all clothing and bedding in hot water typically resolves the infestation. The lice live in fabric, so removing access to their habitat eliminates the problem. Pubic lice are treated with the same types of topical products used for head lice, applied to the affected area.
Why Reinfestation Happens
Lice coming back after treatment is frustrating but common, especially with head lice in school-aged children. The most frequent reason is incomplete treatment. Skipping the second application allows newly hatched lice to mature and start laying eggs. Reinfestation from close contacts who weren’t treated simultaneously is another common cause. When one family member has head lice, checking everyone in the household and treating anyone with evidence of live lice or nits at the same time prevents the cycle from continuing.
In some regions, lice have developed resistance to common over-the-counter treatments. If you’ve carefully followed the instructions on a product and live lice are still present after two full treatment cycles, resistance is the likely explanation. Prescription alternatives work through different pathways and are effective against resistant populations.
Pediculosis in Schools and Communities
Many schools historically enforced “no-nit” policies, sending children home and requiring them to be nit-free before returning. Both the American Academy of Pediatrics and the National Association of School Nurses have recommended against these policies, noting that they cause children to miss school unnecessarily without meaningfully reducing transmission. Nits found on hair after treatment are often nonviable and pose no risk of spreading. A child with head lice can finish the school day, get treated at home that evening, and return the next day.
Head lice outbreaks tend to peak after summer breaks and holidays, when children have had extended close contact with friends and family. Routine head checks at home, particularly after sleepovers or camps, help catch infestations early before they spread further.