Lice are parasites that live on the skin. Most are harmless to overall health, but they cause tiny bites, which can be bothersome.
There are two kinds of lice: chewing lice, which feed on the skin and debris, and sucking lice, which feed on the blood.
Only sucking lice live on humans. Types include head lice, pubic lice, and body lice.
In this article, learn to identify lice by their appearance and where on the body they feed. We also describe the difference between lice bites and bed bug bites.
Head lice are small, gray insects about 2–3 millimeters (mm) in length. They live on the scalp, where they feed on human blood and lay eggs at the base of hair shafts.
The eggs of head lice are commonly known as nits, and they are tiny and translucent. The empty eggshells are white, and they can remain stuck to the hair for up to 6 months. A person is most likely to find them at the nape of the neck and behind the ears.
- do not transmit diseases, though their bites can occasionally expose the host to secondary infections
- lay around six eggs a day
- are transmitted through head-to-head contact and shared objects, including brushes, headwear, towels, and pillows
People can use the following methods to treat head lice:
People can kill head lice using chemicals called pediculicides. Pediculicides are the active ingredients in over-the-counter (OTC) and prescription shampoos and lotions.
Some common pediculicides include:
- Permethrin or any of a group of organic compounds called pyrethrins: These work by attacking the nervous system of the lice. They are available without a prescription and are considered the first-line treatment against head lice. In recent years, however, some lice have developed a resistance to these treatments.
- Spinosad: This is a natural insecticide found in bacteria. It is the active ingredient in the prescription lotion Natroba, which is suitable for children aged 4 years and older.
- Ivermectin: This is available as a topical prescription medication under the brand name Sklice.
Unlike most pediculicides, which tend to kill only live insects, ivermectin can also kill newly hatched nits.
A 2012 study tested the effects of a lotion containing 0.5% ivermectin on louse eggs. The authors concluded that a single application was highly effective, even without combing for nits.
Because some shampoos and lotions may not kill nits, a person should use a nit comb after treatment. Combing helps remove louse eggs.
Even in combination, these methods are unlikely to eradicate all the eggs on the first try.
A person should repeat the chemical treatment and combing after 7–9 days, depending on the type of medication. This is to ensure that any newly hatched lice are killed.
Some insecticides contain toxins that can be harmful, and a person may prefer to use tea tree oil or nerolidol.
A 2012 study tested the efficacy of tea tree oil and nerolidol in killing head lice and their eggs in a laboratory setting. A 1 percent concentration of tea tree oil successfully killed all the lice within 30 minutes.
The same concentration of nerolidol caused half of the eggs to fail to hatch after 4 days.
The authors concluded that a combination of 1 part tea tree oil (at 0.5 percent concentration) to 2 parts nerolidol (at 1 percent concentration) could be particularly effective in killing head lice and their eggs.
However, researchers have yet to show that these oils treat lice effectively and safely in humans, particularly in children.
People can help to prevent the spread of head lice by avoiding head-to-head contact. Doctors also recommend that people, and children in particular, do not share combs, headwear, or pillows.
Pubic lice, also known as “crabs,” infect the genital area. They may also reside in armpit or facial hair. At 1.1–1.8 mm, they are smaller than head or body lice.
Pubic lice are primarily transmitted through sexual contact. Less commonly, a person can get pubic lice by sharing towels, blankets, or clothing.
Signs and symptoms of pubic lice include:
- itching in the genital region or anus, which may intensify at night
- pale blue spots close to bites
- louse droppings, which resemble dark brown powder on the skin or in the underwear
- a low-grade fever
People can use the following methods to treat public lice:
Wash towels, bedding, and clothing on a hot setting, followed by a hot cycle in the dryer.
Also, seal clothing or furnishings that cannot be washed in airtight plastic bags for several days.
Insecticidal lotions are common OTC treatments for pubic lice.
However, pregnant or breast-feeding women should consult a doctor or pharmacist before using these products, due to potential toxicity.
A persistent case of pubic lice may require treatment with a stronger medicine, which a doctor can prescribe.
While condoms help to prevent the sexual transmission of many health conditions, they are not effective in preventing the spread of pubic lice.
The only way to avoid pubic lice is by refraining from sex with someone who has them.
According to the Centers for Disease Control and Prevention, pubic lice are relatively easy to treat and do not carry diseases.
A person with this type of lice should inform all current sexual partners. They can also help to prevent transmission by avoiding any close contact until the lice have been eradicated.
Body lice are between 2.3–3.6 mm in length and tan or gray. They live in bedding and clothing and crawl onto the skin several times a day to feed.
They tend to bite areas of the body where the seams of clothing come into contact with the skin. These include the neck, shoulders, armpits, waist, and groin.
People with body lice may experience itching and rashes if they have allergic reactions to the bites.
Some thickening or darkening of the skin may also occur after prolonged periods of infestation.
- are most often spread through close contact with infected individuals
- are more common in areas with overcrowding and poor hygiene
- can carry bacterial diseases, including typhus, relapsing fever, and trench fever, though these conditions are rare, except in areas of extreme poverty
People can use the following methods to treat body lice:
Wash towels, bedding, and clothing in hot, soapy water and dry them in a machine using a high heat setting.
It is also best to spray furniture with a product that kills lice to eliminate eggs embedded in fabric fibers and seams.
Treatment with pediculicides may also be necessary if body lice persist, despite improvements in housekeeping and personal hygiene.
Practicing good housekeeping and personal hygiene is usually sufficient to prevent a body lice infestation.
When a person finds bites on their body, they may be unsure whether they have body lice or bed bugs. Bed bugs are not lice, but they also feed on human blood.
While body lice exist almost exclusively in areas with overcrowding and unsanitary conditions, bed bugs rarely indicate a lack of cleanliness or personal hygiene.
Bed bugs tend to enter the home on luggage, through shared bedding, or on used furniture.
At around 1–7 mm, bed bugs are larger than lice, and a bed bug infestation can create an almond-like smell. A person may also see discarded exoskeletons in bedding.
While body lice tend to bite during the day, bed bugs bite at night, when the host is lying in the infected area.
Due to their preference for dark places, they are difficult to spot without a flashlight.
Bed bug bites often appear as a line or group of three or more marks. These tend only to cause irritation in people with an allergic reaction to the bugs’ saliva.
People can use the following methods to treat bed bugs:
It is essential to wash infected bedding, linen, and clothing on a hot wash and dry cycle. Brush the mattress seams with a stiff brush to remove bed bugs and their eggs before vacuuming.
Special mattress covers are available, and these can prevent the bugs from entering or escaping. People should also vacuum and declutter the area around the bed.
Body lice can carry diseases, but other types of lice usually cause no lasting harm. Accurate identification is essential for establishing the most appropriate treatment.
If a person is unsure of the cause of bites, they should speak to a doctor for a diagnosis.