Common Questions

Head lice (Pediculus humanus capitis) are tiny parasitic insects that feed on human blood. They primarily live on the scalp but can also be found on eyebrows and eyelashes. Adult lice are about 2-3 mm long, similar to a sesame seed.

Head lice infestations may not always cause symptoms, especially during the first or mild infestations. The most common symptom is itching, triggered by an allergic reaction to louse bites, which can take 4-6 weeks to develop. Other symptoms may include:

• A tickling sensation or the feeling of movement in the hair
• Irritability and trouble sleeping
• Sores on the scalp from scratching, which may lead to bacterial infection

Yes, lice can be treated with over-the-counter or prescription medications, home remedies, or professional lice removal services.

Head lice do not transmit diseases and are not considered a health threat.

Head lice infestations are most common in the U.S. among preschool and elementary school children, as well as their household members and caregivers. Although exact numbers are unclear, an estimated 6 to 12 million cases occur annually among children aged 3 to 11. Research suggests that girls may be more prone to head lice than boys, likely due to more frequent head-to-head contact. Infestations are significantly less common among African Americans, possibly because the type of head lice found in the U.S. may have claws better suited to gripping certain hair types over others.

Head lice spread mainly through direct hair-to-hair contact with an infested person, as they crawl rather than hop or fly. Adult lice live for about 30 days on the scalp but die within two days without a human host. Female lice lay about six eggs daily, and these nits cannot hatch if they are not close to the scalp's warmth. Nits take around 6-9 days to hatch and about a week to mature into adults.
Lice spread most commonly through head-to-head contact, often during activities like school play or at home. Lice infestations are not related to personal hygiene or cleanliness.
Less commonly, lice may spread by sharing:

• Hats, scarves, or hair accessories
• Combs, brushes, or towels
• Lying on bedding, couches, or carpets recently used by an infested person
• Transmission from wigs or hairpieces is extremely rare unless worn in the past 48 hours by someone with lice.

Head lice can survive underwater for several hours and are unlikely to spread in swimming pools. Chlorine doesn’t kill lice, and regular shampoo won’t eliminate them. Specialized lice treatment shampoos are available but often don’t kill lice eggs (nits).

No, animals cannot contract or transmit head lice.

Lice don’t jump or fly; they crawl. The CDC suggests the following to prevent lice:

• Avoid head-to-head contact during play or activities like sports or sleepovers.
• Don’t share hats, scarves, combs, or brushes.
• Disinfect combs and brushes by soaking them in hot water (at least 130°F) for 5-10 minutes.
• Avoid lying on bedding, couches, or carpets that have been used by someone with lice.
• Machine wash and dry clothing, bedding, and towels used by an infested person on a hot setting. If washing isn’t possible, seal items in a plastic bag for two weeks.
• Vacuum furniture and floors where the infested person was, but extensive cleaning isn’t necessary.
• Don’t use fumigants or foggers, as they can be toxic and are not required to control lice.

No, adult lice and nymphs are small, fast, and tend to avoid light, making them difficult to spot. A fine-toothed comb may help. If no lice are visible, look for nits attached to hair shafts within ¼ inch of the scalp, especially behind the ears or at the back of the neck. Nits further than ¼ inch from the scalp are likely already hatched or dead. A magnifying glass may help, as nits can be confused with dandruff or dirt. If only old nits are found, treatment may not be needed. A professional lice technician can confirm the infestation.

Over-the-counter (OTC) lice treatments may not always be effective due to:

• Resistance: Some lice have developed resistance to the active ingredients in OTC treatments, varying by region.
• Incorrect use: Improper application, like splitting doses, can reduce effectiveness.
• Nits: Many OTC shampoos don’t kill lice eggs (nits).

Adult lice can live for up to 30 days on a person’s head but die within 24-72 hours if they fall off. Nits usually die within a week if not kept warm near the scalp, and nymphs can only survive a few hours without feeding.

Head lice are grayish-white or tan and can blend in with hair. Adult lice are about the size of a sesame seed. Nits appear as tiny ovals attached to the hair shaft.