Head lice are small, wingless parasitic insects that are found in human hairs. It also goes by the medical term pediculus humanus capitis. Although head lice can be annoying, it is not a health hazard and is not responsible for the spread of any disease. The Centers for Disease Control do not keep track of the number of head lice cases, because it is not considered a disease. This makes it hard to determine the precise number of cases. But estimates by manufacturers of head lice products indicate that 12 to 25 million Americans get it each year.

A head louse (singular for lice) has 3 life cycle stages: nit, nymph and adult. A nit is a head lice egg. An adult female lays a nit at the base of a hair shaft. This location keeps the nit warm before it hatches. Nits cannot hatch at room temperature. A nit hatches in about 1 to 2 weeks. A nit looks like a yellow, tan, or brown piece of dandruff. Unfortunately, unlike a piece of dandruff, a nit is firmly attached to the hair shaft and cannot be easily removed. Nits normally come in larger numbers than nymphs or adults. Nits are also bigger and easier to see. Nymphs are baby lice and they become adults 7 days after hatching. An adult louse is about the size of a sesame seed. It will take on a darker color if it is found in dark hair. Both nymphs and adults must feed on blood in order to survive. An adult louse can live up to 30 days on a human hair. It can survive for up to 2 days after falling off a human hair.

Determining if you have head lice can be made easier if you know where to look. Nits, nymphs and adult louse are most commonly found on hairs located on the scalp, behind the ears and at the back of the neck. On rare occasions, nits, nymphs and adult louse can be found on the body, eyelashes, or eyebrows.

Even if you know where to look, determining if you have head lice can still be difficult. Medical research indicates that on average, children with a head lice infestation will have no more than 10 to 20 nymphs or adult lice. Because nymphs or adult lice are very small, low in number and able to crawl around hairs pretty quickly, finding them can be a fairly difficult task. If you want to determine if a head lice infestation exists, you might want to use a magnifying glass and bright light to make this difficult task easier.

If there are no nymphs or adult lice, the distance of the nit from the skin can determine if a head lice infestation exists. If a nit is found within a 1/4 inch from the skin, then there is a good likelihood that this person has a head lice infestation. If there are no nymphs or adults and the nits are more than a 1/4 inch from the skin, then this is an old infestation that can be ignored. But there have been cases where a person had a few nits without actually being diagnosed as having head lice, so you should consult your doctor to make sure.

Michael Russell
Your Independent guide to Head Lice

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