In order to deal with the problems of head lice it can be very useful to know about their habits and life cycle in order to deal with them.
Head lice are insects and go through a life cycle. The first stage is as an egg. The eggs are laid by adults on hair close to the scalp. If found much further along the hair, the eggs will generally be old. They are most likely hatched or dead. The eggs are light in colour and described as pearly, grey, whitish, and silvery. They are small and about the size of a pin head.
Lice eggs hatch in 7-12 days. Strictly speaking, nits are the eggs after they have hatched. The lice that emerge are called nymphs. Nymphs grow and molt 3 times before they become adult lice after 9 to 12 days. For this reason, re-treatment should be carried out about 7 days after the first treatment to kill off any juvenile lice (nymphs) that have hatched since the first treatment. A third treatment is also recommended at 14 days to kill off any lice that are late in hatching. By killing nymphs before they grow to adulthood, the life cycle can be broken.
As adults, female lice can lay about six eggs each day with from 50 to 100 eggs being laid before they die. The adults are small being about 3 mm in length, or about the size of a match head. The whole life cycle takes about a month.
Head lice are very specialized and only eat human blood and they only live on the human scalp. Body lice are similar, but not the same.
Head lice are blood-sucking insects that live exclusively on humans. They are usually found on the head, especially around the nape of the neck and the area behind the ears. They are especially common in school children between the ages of three and twelve. Body lice look very much like head lice, but tend to inhabit other areas of the body.
The first indication of head lice is usually itching and scratching caused by the bloodsucking habits of the louse. Examination of the hair and scalp will reveal white or grayish crawling forms (about the size of a sesame seed but with six legs) and yellowish white eggs attached to the hair shafts close to the scalp. The eggs are sometimes mistaken for dandruff, or residues of shampoo, that will not wash off. Red bite marks or scratch marks are often seen on the back of the neck. There are a number of other reasons for itching and scratching, of which dry air alone can be a culprit, and so ideally, the lice need to be identified. Lice eat several times a day, injecting irritating saliva into the wound to prevent coagulation. Scratching the scalp can result in infections. As it typically takes several weeks exposure to the lice before an allergy to the bites develops, itching is a sign that the infestation has been present for a month or more, or that the person has already developed an allergy because they have been infested before. So, a lack of itching does not necessarily mean that the person is not infested.
Head lice do not hop, jump or fly and can only be transmitted from one person to another by either close head to head contact (95% of lice are transmitted in this way), or by the sharing of objects such as combs or brushes, hats, coats, furniture pillows or bed pillows. So, as well as using a treatment to kill the lice and their eggs, it is essential to break the cycle by taking steps against reinfestation by making sure that any contacts are also treated.