Headlice, also known by their scientific name of Pediculus humanus capititis, are small, wingless parasites that feed off the human scalp. They are most commonly found behind the neck at the base of the skull and behind the ears. Their eggs are known as nits, and are the most obvious identifying feature of an infestation. Although the nits can be mistaken for dandruff, on a closer look, the eggs are oval-shaped. They are also very tricky to remove from the individual hair they are attached to.

The nits will hatch in about a week and the baby lice are called nymphs. They look just like the adults only they are smaller. The nymphs become adult lice after about seven days. The adult louse has a lifespan of approximately thirty days and they feed on blood. A louse will have six legs and each leg will have a claw at the end that is hook shaped. They use these claws to attach themselves to the shaft of the hair. It can be very hard to treat a case of headlice because the louse and nits will attach themselves so firmly to the hair and it can be hard to remove them.

An infestation of headlice can result in a range of symptoms, especially a strong itch at the base of the skull, tickling and crawling sensations across the scalp, and sore patches on the scalp where the head has been scratched. While it is possible to catch sight of adult lice, they are generally too quick and can manage to avoid being detected. An infestation is usually diagnosed when the above symptoms are presence, as well as from the nits themselves.

While headlice is thought of as being synonymous with poor hygiene, even the conscientiously clean can contract lice and nits. Regular soaps, shampoo, and detergent do little to stop these blood-suckers. The only sure way to kill lice is by pulling them off of the hair, a time-consuming and tedious process. There are special combs that can aid this process. Also, various medications may be used, either with or without a doctor's prescription.

Over the counter lice treatment shampoos containing pesticides pyrethrins or permethrin are available, sometimes together with the special "nit-picking" comb that is needed to detach nits from the hair. Alternatively, a prescription medication such as malathion or lindane is available. Not only the diagnosed person should undergo treatment, but also all the other members of the household who are infected. Washing the bedding and clothing worn by the infected person is needed, and after treatment the comb should be used to pick dead lice and nits from the hair.

There are many home remedies for head lice, such as soaking one's head in various liquids (examples include mouthwash containing alcohol, vinegar, shampoo, and mayonnaise).