The head louse (Pediculus humanus capitis) is a parasitic insect spending its entire life on human scalp and feeding exclusively on blood. Humans are the only known host of this parasite.During its lifespan of 4 weeks a female louse lays 50-150 eggs (nits). The egg hatches to the first nymphal stage, which after three moltings develop to nymph 2, nymph 3 and eventually to either a male or female louse.

Adult head lice mate frequently, and females lay approximately 3-4 eggs each day. Generations last for about 1 month. Each stage of development feeds on blood, which they harvest by biting the skin 4-5 times each day. During oviposition, females excrete a glue-substance from a gland located on the posterior of their body. This substance attaches the heads to the hair of the host. While lice may colonize any part of the scalp, they favor the nape of the neck and the area behind the ears, where eggs are often laid.

The most characteristic symptom of infestation is pruritus on the head which normally intensifies 3 to 4 weeks after the initial infestation. The bite reaction is very mild and it can be rarely seen between the hairs. Bites can be seen, especially in the neck of long-haired individuals when the hair is pushed aside. In rare cases, the itch scratch cycle can lead to secondary infection with impetigo and pyoderma. Swelling of the local lymph nodes and fever are rare. Head lice are not known to transmit any pathogenic microorganisms.

Head lice are extremely difficult to get rid of as there is no over the counter product that effectively kills 100% of the eggs laid. Common treatments include chemical shampoos, hot air, combs with tiny teeth to "pick the nits," cutting hair or shaving the head and herbal washes. Kerosene is never recommended for use in ridding someone of lice. Hair bleaching and dyes do not work. Some people try antibiotics, ivermectin, garlic and Vitamin B for prevention, with varied results.

Despite countless efforts to eliminate head lice, the pests have a strong reputation for resistance. As with other "superbugs" in today's medical and scientific age, head lice are becoming increasingly aggressive against treatments commonly used today. It is believed that up to 80% of lice are capable of resisting unprescribed methods, including chemicals such as permathrin and phenothrin.

An infection of head lice is notoriously difficult to treat, so prevention needs to be the first priority. Scientists have found that many lice have developed a resistance to most lotions currently used, through natural selection. As a result, there is now a scramble to develop new treatments that will effectively eliminate lice. In the meantime, teachers, parents, and children are left to their own devices.