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The life cycle of a louse occurs in three stages across a few weeks. They grow from eggs into nymphs and then become adults. Having head lice is a common problem, especially among children, and they cause intense irritation and itching. Repeated scratching can break the scalp’s skin, leading to an infection. The Centers for Disease Control and Prevention (CDC) estimates that 6–12 million infestations occur annually in the United States among children aged 3–11 years. From an egg until its death, a complete life cycle of a louse lasts for a maximum of 35 days. Understanding the life cycle of lice is essential in effectively dealing with a lice infestation. Read on to learn about the life cycle of lice, how they spread, and more. What is the life cycle of head lice Share on PinterestIllustration by Maya ChastainThe life cycle of a louse occurs in three stages: eggnymphadult Below is a timeline of a louse’s life cycle.The louse emerges after 6–7 days.The first molt occurs two days after hatching.The second molt occurs 5 days after hatching.The third molt occurs 10 days after hatching.Emerging from their third molt as adult lice, the female and slightly similar male begin to reproduce.The female lays her first egg 1–2 days after mating.The female can lay approximately 3–8 eggs per day for the next 16 days.The louse dies, having lived for 32–35 days. Eggs Doctors call head lice eggs nits. They are small, are 0.8 to 0.3 millimeters (mm) in size, and appear as oval- or teardrop-shaped eggs. Their color may range from white, yellow, tan, or brown, so they may be hard to see. Eggs look darker when alive and pop between the fingernails. In contrast, hatched eggs look pale to almost translucent. Their sides look shriveled when the eggs are dead from lice treatments. A female adult attaches each egg to individual hair shafts about 6 mm from the scalp to maintain an ideal temperature for hatching. It uses a strong cement-like substance that keeps the egg resistant to bathing, chemicals, and hairstyling. Nits take 6–9 days to hatch. They need the warmth of the scalp for incubation, but if they become dislodged from the hair, they will most likely die before they hatch. Nymphs Baby lice or larvae are called nymphs. They look like miniature adult lice, about the size of a pinhead, or 1.1–1.3 mm. They crawl to the scalp to feed on blood daily. Nymphs undergo three stages of molting or shedding skin before entering the adult stage. The entire process takes up to 10 days:The first molt occurs 2 days after hatching.The second molt occurs 5 days after hatching.The third molt occurs 10 days after hatching. Adult An adult louse develops from the third molt, and it is darker in color, ranging from tan to grayish-white to brown. They are around the size of a sesame seed, or 2–3 mm. Females are usually larger than males. Adult lice can begin mating. Females lay their first egg 1–2 days after mating. They can lay up to eight nits per day and produce eggs for the entire duration of their lifespan. A mated female only needs to mate once to continuously produce eggs because they can store sperm in their bodies. They need to have bloodmeals several times a day and can live up to 30 days on a person’s head. However, a louse can only survive up to 2 days off the host and die from lack of food and optimal temperature. Learn more about head lice. Symptoms Many people with head lice have no symptoms at all. However, if others are experiencing the following symptoms, it could indicate head lice:frequent itching of the head or scalpredness or inflammation on the scalp or near the hairlinetiny red bumps or sores from scratching Learn more about the symptoms of head lice. How do they spread Lice cannot fly or jump. They can only crawl from one individual to another, so the most common way they spread is through head-to-head contact. This interaction is common during playtime at school, home, parties, and playgrounds. Lying on the bed, couch, or carpet and using a recently used pillow can also promote the spread of lice. Lice can also transfer to another person through shared belongings and clothing such as hats, ribbons, brushes, and towels. They can only feed on human hosts, so pets, such as dogs and cats, cannot spread lice. Learn more about what causes lice. How do you treat them It is essential to treat lice immediately and thoroughly to avoid an infestation and reduce their spread. Doctors will only recommend treatment for people with a diagnosis of an active infestation. If a person with lice has a bedmate, they also require treatment. If a child under 2 years has allergies, it is best to consult a doctor before applying any medication to their hair. Treatments include creams and medicated shampoos, and some are available over the counter, while some need a prescription. Over-the-counter (OTC) medications include Pyrethrins, such as Rid and Pronto, or Permethrin lotion, such as Nix. Doctors may also prescribe prescription medications. These include:Benzyl alcohol lotion (Ulesfia) Ivermectin lotion (Sklice)Malathion lotion (Ovide)Spinosad (Natroba) Individuals should check the specific instructions for the medication and pay close attention to how long they should leave the medication on their hair and how they should wash it. If, after 8–12 hours, the lice seem to move slower following treatment, the medication may be effective but is taking longer to kill all the lice. A person can use a fine-tooth nit comb to remove the hair’s remaining live lice and dead ones. An individual should continue rechecking weekly for 2–3 weeks for remaining signs of lice or nits. Retreatment may be necessary to kill remaining nymphs before they can produce new eggs. However, if they remain as active as before, the lice may be resistant to a person’s medication. They may try a different OTC or prescription product. If a person requires more advice or information on treating lice, they can also consult a doctor. Learn how to get rid of head lice. Prevention A person can take the following measures to help prevent and control lice spread:avoiding close personal or hair-to-hair contact while playing or doing activities at school, on playgrounds, or anywhere elseavoid sharing clothing such as coats, uniforms, ribbons, and hatsusing a specific comb or brush for the child and never share them with others never borrow brushes or combs from other childrensoaking brushes or combs in hot water for a minimum of 5 minutesstoring items that a person cannot wash in a sealed plastic bag for 2 weeks to starve the licevacuuming furniture, carpets, rugs, and the floormachine washing bed linens, clothing, and other items that a person wore or used Teaching children to avoid activities that may spread head lice can help prevent lice outbreaks in schools, camps, and communities. Summary Head lice are insect parasites that live on the human scalp to reproduce and feed on its blood. While it is not dangerous, a lice infestation can cause severe itchiness and irritation, leading to secondary infections. A louse has three stages in its life cycle. They begin as nits, hatch and become nymphs, and become full-sized adults within weeks. Their life cycle is fast, and they tend to reproduce quickly. Treatments in the form of lotions and medicated shampoos can kill nits, nymphs, and adult lice. However, a person should follow the instructions on the box or label to ensure its effectiveness. Individuals can also supplement treatment with preventive measures, such as washing clothes and items someone with lice has used, vacuuming the floor and furniture, and preventing head-to-head contact as much as possible. Last medically reviewed on May 30, 2022Dermatology 4 sourcescollapsedMedical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.About head lice. (2016).https://www.health.vic.gov.au/infectious-diseases/about-head-liceEpidemiology & risk factors. (2019). https://www.cdc.gov/parasites/lice/head/epi.htmlFrequently asked questions (FAQs). (2020). https://www.cdc.gov/parasites/lice/head/gen_info/faqs.htmlTreatment. (2019).https://www.cdc.gov/parasites/lice/head/treatment.htmlFEEDBACK:Medically reviewed by Amanda Caldwell, MSN, APRN-C — By Rachel Ann Tee-Melegrito on May 30, 2022 Latest newsWhat sets 'SuperAgers' apart? 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