What Are the Different Types of Lice?
Three different types of lice infest people.
- The head louse is a grey-white animal about 2 mm-3 mm in length (about the size of a sesame seed). The life span of the female louse is about one month. During this time, she will produce between seven to 10 eggs ("nits") per day and attach them firmly to the hair shaft region close to the scalp or body. These grayish-white nits, which resemble dandruff, are attached with a cement-like, water-insoluble substance that makes them difficult to remove. After six to 10 days, the oval-shaped nits hatch as nymphs and become adults in 10 days.
- Head lice are the most common form of lice infestation. The U.S. CDC reports that 6-12 million people in the United States are infested each year. Children aged 3-11 years in preschool, elementary school, and day care centers are most likely to have lice. All socioeconomic classes are affected. Girls are more commonly infested, but hair length or personal hygiene are not predictive factors. Due to unique hair characteristics, African Americans are less commonly bothered by head lice.
- Head-lice transmission is most commonly via direct head-to-head contact. Sharing pillows, caps, headphones, and combs/brushes are notorious ways to transmit head lice. Since the head louse dies due to dehydration within two days if not feeding on their human host, contact with carpeting and couches is less commonly seen as a route of transmission. Most lice infestations are asymptomatic (meaning they cause no symptoms). However, if symptoms are present, itching of the scalp, neck, and behind the ears are the most common complaints. Intense scratching may lead to secondary skin infections (for example, impetigo) and associated enlargement of the lymph nodes of the neck and scalp regions.
- The diagnosis is made by demonstration of the adult lice or nits. Nits are more easily seen when examined using a Wood's light ("black light") that causes them to fluoresce as pale blue objects attached to the hair shafts near the scalp. A fine-tooth comb run through the hair will also demonstrate adult lice and nits.
- The body louse is slightly larger than the head louse but has the same general appearance. Unlike the head louse, which lives on its human host, the body louse lives in clothing (commonly in the seamed areas) and then transfers to the human host to feed. The life cycle of the head louse and the body louse are similar in character and duration. An important difference, however, is the ability of the body louse to survive for up to 30 days away from its human host.
- Body-lice infestation is a prominent public health problem in communities with large populations dealing with poverty, overcrowding, and poor personal hygiene. Reused mattresses and bed linens as well as communal beds are risk factors.
- Itching is the primary symptom of body-lice infestation. Areas where seams of clothing are tightly adherent to the body are the most likely areas of involvement. Waistband lines, and axillary and bra strap regions, are examples of where excoriation (crusts, abrasions, or scabbing) from scratching is commonly noted. Red, itchy bite marks may be seen on the body.
- The diagnosis of body lice involvement can be made by identifying lice or nits in clothing, bedding, or linens -- especially in the seam regions.
- Bedbugs are related to lice. They hide among sheets, blankets, and in furniture and really do bite during the night when they seek a warm body for a meal. They usually leave brown or black markings on the bed linens and bite in rows, often leaving three or more linear bite marks.
- The pubic louse ("crab louse") is distinct morphologically (somewhat rounded with three pairs of legs on either side of the body from which it takes its descriptive name) from the head and body louse. The female life span is slightly shorter (three weeks), and she produces fewer eggs per day (three) than her counterparts. The eggs attach to the base of the pubic hair shaft for approximately six to eight days before hatching.
- In adults, pubic lice is transmitted by direct sexual contact; children generally contact the infection via nonsexual transmission from their parents. (Sexual transmission is possible in cases of sexual abuse.) Transmission by bed linens and infested clothing is less likely and doubted by some.
- Intense itching of the pubic area is characteristic. Axillary regions, eyelashes, and even the scalp may be involved. Nighttime symptoms are may be more intense. After being bitten, a bluish-colored sore may develop in the involved areas. The diagnosis is established by demonstration of crab-shaped lice attached to the hair shaft. Consideration of infection by other sexually transmitted diseases (STDs) should be entertained in any adult with pubic lice. Condoms do not prevent pubic-lice infestation. Contrary to popular thinking, pubic lice are not spread by toilet seats.
What Are the Causes And Risk Factors for a Lice Infestation?
Picture of pubic louse (crab)
Head, body, and pubic lice are transmitted person to person. It cannot be transmitted via pets. On the other hand, the different lice types have variable durations that they can survive on fomites (inanimate objects -- for example, sheets, pillows, hair brushes, etc.). Avoidance of potential exposure is helpful. Don't use others' combs or hairbrushes. Don't wear others' caps, headphones, or earbuds. Don't sleep in bed linens of others if you have suspicions of lice infestation. If you visit a residence that has had a lice infestation, make sure that the sofas, pillows, beds, etc., have been appropriately cleaned and inspected for the absence of lice. The belief that one can get a pubic lice infestation from a toilet seat is untrue.
What Are the Symptoms and Signs of a Lice Infestation?
- Lice infestation on the human body (also known as pediculosis) is very common. Cases number in the hundreds of millions worldwide. While lice can occasionally cause significant illness (typhus, relapsing fever, and trench fever), a lice infestation is generally more of an itchy and embarrassing experience than a serious medical problem. Three distinct presentations of lice infection exist and each is caused by a unique parasite.
- Head lice (Pediculus humanus capitis) is by far and away the most common infestation and favors no particular socioeconomic group. A genetically close "cousin," Pediculus humanus corporis, is responsible for body lice and is more commonly associated with poverty, overcrowding, and poor hygiene. Pubic lice ("crabs") is caused by Pthirus pubis and is transmitted by intimate and/or sexual contact.
- Lice infestation is a uniquely human experience. Lice do not jump or fly from host to host. They cannot be transmitted via animals but may be transferred by person to person via direct contact and by fomites (inanimate objects -- for example, caps, combs, sheets, etc).
Common Childhood Skin Disorders
When Should Someone Seek Medical Care for Lice?
Life cycle of lice. Image courtesy of DPDx Identification and Diagnosis of Parasites of Public Health Concern, Parasite Image Library, Centers for Disease Control and Prevention.
When to Call the Doctor
While lice can easily and effectively be treated with home care methods, call your doctor if these conditions develop:
- If skin or scalp infections develop from scratching with symptoms such as discharge, redness, swelling, pain, or tenderness of the area
- If home treatment doesn't work after using over-the-counter medications as directed (see below)
- For further testing for sexually transmitted diseases (if pubic lice are discovered)
- If itching continues even after treatment with over-the-counter antihistamines
- If lice persist and treatment has failed
When to Go to the Hospital
- If infections from scratching are not improving, are worsening while you are on medications, or if other symptoms develop such as fever, chills, nausea, and vomiting
- If you develop an allergic reaction to medications (indicated by a rash, swelling to the lips or tongue or if you have any trouble breathing)
What Specialists Treat a Lice Infestation?
Primary care physicians (pediatricians, internists, and family practitioners) are all capable of making the correct diagnosis and providing therapy for a lice infestation.
How Do Health Care Professionals Diagnose a Lice Infestation?
Based on the finding of lice and nits on the scalp, genital area, body, or on clothing, the doctor can suggest home care techniques and prescribe medications as necessary. No other tests are usually performed to diagnose lice.
Are There Home Remedies That Get Rid of Lice?
Unhatched nit of head louse, Pediculus humanus var capitis. Photo courtesy of Centers for Disease Control and Prevention/Dr. Dennis D. Juranek.
If lice are seen in a school-aged child, notify the school nurse or teacher in order to limit the spread.
- Head lice
- Search for a head lice infestation when hair is wet. Use a fine-toothed comb (or a louse comb), clear tape (to stick on hair to pick up lice eggs), a magnifying glass, and a strong light. A comb used to remove fleas from dogs and cats works well to remove head lice.
- Wet combing should be done every two to three days over a two-week period, with small sections of hair, working out from the scalp. Some call this "bug busting," and it can be very effective. The entire scalp should be inspected, not just the neck region.
- If lice are found, treat with an anti-lice agent and repeat in seven to 10 days to kill newly hatched nits.
- How to use anti-lice agents: Over-the-counter treatment is available and should be used first. If after two applications, lice are still present, then prescription anti-lice agents may be needed. Apply the anti-lice agent to dry hair for the time listed on the product (usually 10 minutes). Shampoo and rinse hair and comb as directed with a fine-toothed comb. Repeat anti-lice treatment in seven to 10 days to kill nits that may have hatched.
- Nonprescription anti-lice agents include Nix Lotion (permethrin 1%) and Rid, A200, and Pronto shampoos (pyrethrin products).
- Check all household members and treat only if lice or nits are seen. Pyrethrin kills only lice. It does not kill nits and thus requires retreatment seven to 10 days later to kill the newly matured lice. Permethrin kills both nits and newly hatched lice for several days after treatment. However, a repeated treatment is also recommended seven to 10 days later for optimum results. Current recommendations favor Permethrin over Pyrethrin as a first-line treatment.
- If a child is younger than 2 years of age, comb to remove lice and nits but do not use over-the-counter anti-lice agents. A prescription product is available from your doctor.
- Hair conditioners may coat or cover the lice, so they should not be used before applying anti-lice agents.
- Wash all bed linens and clothing that have been in contact with the infested person in the past two days. Use hot water and the hot cycle in the dryer.
- Some recommend that water be at least 140 F to effectively kill the lice and nits. Most hot-water heaters are set at 120 F for child safety. This lower temperature may be effective.
- All non-washable items such as stuffed animals should be placed in plastic bags for two weeks then opened outdoors. Dry cleaning may be an alternative.
- Disinfect combs and brushes in hot water or rubbing alcohol. Soak for more than five minutes in very hot water (greater than 131 F or 55 C).
- Vacuum floors and furniture, especially couches and areas used by children. Throw away the vacuum bag immediately.
- Herbal therapy and oil treatments (for example, olive oil, butter, petroleum) have been used in an attempt to suffocate lice. A small study done in 2004 did not show any benefit of these measures.
- Do not use gasoline, kerosene, or oils. Burns have occurred. A comb using an electric current generated by an AA battery has been developed but any reported success is anecdotal and has not been scientifically proven.
- Do not shave the person's head. This drastic measure is not necessary.
- Treatment failures commonly reflect repeated exposure to those untreated and infected or lack of compliance with therapy. While resistance is growing to topical treatments, resistant infestation will often respond when an alternative product is used. It has been recommended that, should reinfestation occur within one month after successful treatment, an alternative topical insecticide should be used.
- Body lice
- Wash the body thoroughly.
- Wash and dry all bed linens and clothes in hot cycles. Destroy what you can because these nits can survive longer without human contact (up to 30 days).
- Anti-lice agents are usually not needed if clothing is thrown away and bed linens are thoroughly washed.
- Check all household members or close contacts. Treat them only if lice or nits are seen.
- Vacuum floors and furniture. Throw the vacuum bag away immediately.
- Chemical insecticide sprays in the home are not effective and not recommended.
- Use over-the-counter antihistamines (such as diphenhydramine, [Benadryl]) for itching.
- Pubic lice
- Treat with anti-lice agents and repeat in seven to 10 days.
- Remove nits with a fine-toothed comb.
- Check all close contacts. Treat them only if lice or nits are found.
- Wash and dry all clothes and bed linens in hot cycles.
- Check eyelashes and eyebrows. If lice or nits are seen, apply petroleum jelly (Vaseline) twice daily for eight days.
- Use over-the-counter antihistamines (such as diphenhydramine) for itching.
How to Get Rid of Lice
- Family members are encouraged to look for lice routinely because it can recur.
- Safe sexual practices may lower the risk of transmitting pubic lice and other diseases.
- Wash clothes, bed linens, combs, brushes, and other personal items to prevent recurrence.
- Preventive treatments with anti-lice agents are not recommended and can lead to illness and persistent itching.
Nymph of head louse, Pediculus humanus var capitis, about to emerge from egg. Photo courtesy of Centers for Disease Control and Prevention/Dr. Dennis D. Juranek.
What Medications Treat Lice?
Follow the doctor's instructions for prescription anti-lice agents, if prescribed.
- Do not apply to eyes, face, or mucous membranes.
- Discuss treatment with the doctor if you are pregnant.
- Common prescription anti-lice agents
- Elimite cream (permethrin 5%) may be used in children over 2 months of age.
- Kwell shampoo or cream (lindane 1%) is generally considered a "last ditch" medication due to the possibility of neurotoxicity enhanced by absorption through open sores or excessive application. Guidelines recommend that patients weight at least 110 pounds to use this treatment.
- Ovide lotion (malathion 0.5%) may be used in children over 6 years of age. There are few side effects (stinging when open sores are exposed). It is an alcohol-based preparation and thus hair dryer and curling iron use should be avoided due to a potential flammable reaction.
- Ulesfia (benzyl alcohol 5%) is a new product useful for head lice only and may be employed for patients over 6 months of age. Since it does not kill the nits, a second treatment is necessary seven days after the initial treatment.
- Sklice (ivermectin lotion, 0.5%) is another new product that can be used on people over 6 months of age. It kills both nits and lice and thus needs only a single application.
- If you have ragweed allergies, avoid permethrin (Elimite, Nix) and pyrethrin (Rid, A-200) products.
- Lindane is considered a second-line treatment if other lice medicines fail or are not tolerated. It is not very safe in children and may cause neurotoxicity (dizziness, seizures).
- Studies in 2001 demonstrated that combination therapy using topical 1% permethrin (Nix) and the oral antibiotic trimethoprim/sulfamethoxazole (Septra or Bactrim) was effective for head-lice infestations which were poorly responsive to traditional therapies.
What Is the Prognosis for a Lice Infestation?
With appropriate home care or prescription medication, more than 90% of lice infestations can be cured.
Is It Possible to Prevent a Lice Infestation?
As for many contagious conditions, avoidance is key. This is accomplished by not using others' hairbrushes, combs, hats, or similar objects. Since lice may remain on sofas pillows and bed linens, vigorous cleaning of any place that an individual with lice has frequented is paramount. Sleeping only on surfaces that have no history of lice exposure is critical to prevent body lice infestation. Safe sex practices can help limit transmission of pubic lice.
- Treatments are more effective in killing lice than nits. This is why combing with nit combs is so important to remove nits -- as is repeating the anti-lice treatment in seven to 10 days.
- Children can return to their usual activities and school or day care after the first treatment, even if nits are still in the hair. Re-treat in seven to 10 days as discussed above.
Reviewed on 4/17/2020
Devore, Cynthia, et al. "Head Lice." Pediatrics 135.5 May 2015: e1355-e1365.
Pickering, Larry K., Carol J. Baker, David W. Kimberlin, and Sarah S. Long, eds. 2009 Red Book: Report of the Committee of Infectious Diseases. 28th edition. Grove Village, IL: American Academy of Pediatrics, 2009.
Wychoff, Alyson. "Parent Plus: Over the Counter Medications Still First Line Lice Fighting Strategy." AAP News Apr. 11, 2016.