There are three kinds of lice which live and feed on human blood. Head lice, body lice and crab lice. Typically head lice are isolated to the head; body lice are found over most of the torso and crab lice are found on the pubic hair. Lice are very tiny parasitic insects with six legs and two antennae. Body lice aren't found commonly in developed countries because normal housekeeping prevents their spread. They have flourished historically in places where people live in cramped unsanitary conditions.

Head lice, however, are at near epidemic proportions. Despite normal hygiene and housekeeping they have become a normal part of primary classroom concerns. Since 1983 a non-profit organization has worked to raise public awareness of this subject. The National Pediculosis Association operates a website with games for children and information for adults.

A number of children's books are also to be found which attempt to educate children as to the nature of this childhood infestation. Shampoos containing the pesticides permethrin, pyrethrin or malathion have been used for many years in non-prescription treatments for head lice.

One of the problems that has caused the current level of outbreaks is that the insects are evolving to be resistant to the insecticides which have been used traditionally to combat these lice. This is becoming a common problem recently in agricultural and medical realms as microorganisms are becoming resistant to antibiotics and insects are becoming resistant to pesticides..

These lice are usually passed from one person to another. Although they can be passed on objects that are used by more than one individual it is less common. These insects feed very frequently and die if without a host for even a short time. The nits however take about two weeks to hatch and these can be attached to fabric fibers. Combs are especially culpable in transporting head lice and nits from one person to another. Hair care items should not be shared unless thoroughly cleaned before hand.

It only takes one adult female head louse to start an infestation. A head louse will live about six weeks total and will be mature enough to lay eggs for the last month of that lifecycle. During that time a head louse could lay as many as 100 nits. They begin biting and sucking blood soon after hatching. They attach three mouth parts called stylets and inject a substance which prevents blood clots from forming while they feed. This substance is responsible for much of the itching associated with lice.

Once one adult head louse is on someone's head the numbers swell by geometric proportions. If the head becomes over crowded they could migrate to the eyebrows and eyelashes. These insects are very quick and hard to see. Checking for nits attached to the hair is the usual manner of diagnosis. The nits are tiny and white so that the trained eye can recognize them very quickly.

The occurrences of head lice are so frequent that most grade schools conduct regular head lice checks. If nits are found the parents or guardians are notified about the infestation and advised about treatment methods. If these instructions aren't followed to the letter the lice will recur and the whole process must be repeated.