Lice are barely visible blood-sucking parasites that live on hairy parts of the human body.
Lice seldom cause serious medical problems, but are very contagious and can be annoying.
Intense scratching can break the skin and lead to bacterial infections.
There are three types of lice: head lice, body lice and pubic lice. Treatment depends on the area infected.
Contrary to popular belief, head lice are not related to poor hygiene.
Treatment must kill the adult lice and eggs (nits) on the body, bedding and clothing to be effective.
Lice are barely visible, wingless insects between 1 and 3 mm in size that live on human beings and feed on blood. These parasites seldom cause serious medical problems, but are annoying and very contagious, spreading easily from person to person by body contact and shared clothing and other personal items. Every four hours or so, a louse bites into a tiny blood vessel for a meal. Because it injects an anaesthetic, you won’t feel the initial bite. However, as its saliva gets under your skin, bites begin to itch. Intense scratching often breaks the skin, and can lead to bacterial infections.
Head lice (Pediculus humanus capitis) are about the size of a sesame seed, and can easily be seen, although they hide quickly when exposed to light. Their eggs, called nits, are barely visible whitish ovals cemented to hair shafts.
Head lice are spread by personal contact and by shared brushes, combs, hats and other personal items. The infestation sometimes extends into the eyebrows, eyelashes, and beard. Head lice are a common scourge of school children of all social strata.
Body lice (Pediculus humanus corporis) look very much like those found on the head, but are actually a different species. While they aren’t as easily transmitted as head lice are, they are more difficult to spot, hiding in the seams of clothing and folds of bedding when not actually feeding.
Body lice infestation is usually found in people who have poor hygiene and those living in close quarters or crowded institutions. These lice can carry diseases such as typhus, trench fever and relapsing fever.
Pubic lice (Phthirius pubis) are yellow-grey insects found in the pubic region, and are typically spread during sexual contact. The size of a pinhead, they are slightly translucent and barely visible against light-coloured skin. With their shorter, rounder body shape and crab-like claws with which they cling to hair, they resemble crabs – hence their popular name. The eggs, which are barely visible, are tiny white particles glued so firmly to hair shafts that they cannot be removed by normal washing.
Contrary to popular belief, contracting lice is not related to poor hygiene – in fact, head lice are thought to prefer clean hair to dirty hair. However, good hygiene can combat body lice.
Head lice: intense itching on the scalp, especially behind the ears and at the nape of the neck. Children may hardly notice head lice or may have only a vague scalp irritation in the beginning. With advanced infestation, the scalp may become red and inflamed, with swollen glands near the area where the lice are living.
Body lice: itching is generally most intense on the shoulders, buttocks and abdomen. Signs of lice include unexplained scratch marks on the body, hives, eczema, or small red pimples on the shoulders or torso. If the lice are not treated, welts may develop.
Pubic lice: Pubic lice causes continual itching around the penis, vagina and anus, and perhaps a rash.
Lice live successfully all over the world, wherever people gather in close proximity, for example in schools.
Once you have been infected with adult lice, they will attach their eggs (nits) to hair shafts on various parts of the body. The nits hatch in eight to ten days, producing more lice. Lice can live up to a week on items such as bedding, sleeping bags, clothing and towels.
When to see a doctor
Call your doctor if you need help getting rid of lice, or if scratching has led to an infection.
Head lice: itching and scratching is the hallmark of this condition. Your doctor will examine the scalp for tiny grey insects, usually at the nape of the neck or back of the head where there is the most hair. The doctor will also look for shiny, small, greyish-white oval-shaped eggs (nits) firmly stuck close to the base of hair shafts. They look like flakes of dandruff that cannot be brushed off.
Body lice: Because body lice are difficult to spot, intense itching on the shoulders, buttocks and abdomen, together with unexplained scratch marks on the body, hives, eczema, and small red pimples on the shoulders or torso are taken as signs of their presence.
Pubic lice: Pubic lice are particularly difficult to find and may appear as tiny bluish spots on the skin. However, they do leave a scattering of miniscule, dark-brown specks (louse excrement) on underwear where it comes into contact with the genitals and anus, and these can form the basis of a diagnosis.
The goal of treatment is to remove all lice and nits. This usually requires repeated efforts, because a few adult lice may escape by hiding in clothing or bedding, and eggs are difficult to kill.
The most common treatment for head lice is to kill the adults with an insecticidal shampoo and to clear out the nits with a special fine-toothed comb. Of the medications for lice, permethrin is the safest, most effective, and most pleasant to use, and is available over the counter. For best results, follow the directions exactly. Other family members should be treated too – about 60% of infected children have relatives who carry lice.
To eliminate all lice and successfully prevent reinfection, wash all clothing, towels and bed linen in hot, soapy water, and dry them in a hot dryer. You can also disinfect bedding and other items such as hats and clothing by placing them in a sealed plastic bag for 14 days; the nits will hatch in about a week and die of starvation. Brushes and combs can be disinfected by soaking them in hot, soapy water for 10 minutes.
If you prefer to avoid the use of insecticides, try a "combing only" technique. Wash the hair with an ordinary shampoo and conditioner and leave wet. With a fine-toothed comb, stroke slowly outward from the roots through one lock of hair at a time. Lice will land on the back of the comb, get caught between the teeth, or fall off. Space at least 30 strokes over the head. Repeat every three days. Because new-born lice do not lay eggs for the first week, all lice should disappear after about two weeks of combing.
To treat body lice, wash the entire body with soap and water. If this is not effective, you may have to use an insecticidal preparation, which usually kills all the lice. Wash all clothing and bedding in hot water and dry them in a hot dryer. Store clothes for two weeks in sealed plastic bags or place them in dry heat of 60 °C for three to five days.
Pubic lice can be treated with non-prescription medications containing pyrethrins (natural insecticides). Sexual partners will also have to be treated. "Crabs" are sometimes found on eyelashes and eyebrows, where they are difficult to treat. Remove them with tweezers, or use an ophthalmic ointment such as physostigmine. Ordinary petroleum jelly may kill or weaken lice on eyelashes too.
Prevention of head lice is difficult, especially among children, since lice spread quickly from head to head. To help prevent lice, prevent children from sharing hats, hooded coats, scarves, combs, brushes, pillows, and soft toys. If you discover lice on your child, notify school or day-care authorities immediately, since classmates are likely to be infected. Infected children should be kept home from school until they are treated.
The best way to prevent lice in the genital area is monogamy or avoidance of intimate sexual contact. Condoms are not a good protection against lice because they do not cover the hairy areas where the lice live. You should also avoid contact with contaminated clothing, bed linen and toilet seats.
Reviewed by Prof H.F. Jordaan, MBChB, MMed (Derm).