It is generally recognised that only the discovery of a live moving louse constitutes a head louse infection, the presence of eggs or nits, or an itchy scalp, does not.
The things you may find if you have a head louse infection are described below:
- Lice; brown or black insects identifiable by the naked eye in various sizes
- Translucent or Brown Eggs; these eggs have a louse inside, though it is not possible to tell whether these eggs are alive or dead.
- Dark Brown or Black Eggs; these eggs are likely to be old and dead. Their position further away from the scalp would indicate that they were laid some time ago as new eggs are laid close to the scalp.
- White (Snowy) Eggs; these eggs are empty egg shells, called ‘nits’, again their position will indicate how long ago they were laid.
- “Pepper dust” on the pillows / clothes; these are the droppings of the louse (there is no urine as water is lost through evaporation).
Head lice are passed from one person to another through close head to head contact. There is debate over whether transmission via objects such as hats, combs and bedding can occur, since the louse can survive for a short while away from the human host. However it is generally agreed that this is not possible and that lice found away from the head should be considered to be dead or dying and an unlikely cause of any further infection.
Infection is common among children, since lice are passed through head to head contact, which occurs regularly at such an age. There is some evidence that the infection is more common in girls than boys, this is thought to be due to the ‘close play’ that is more common amongst girls.
A head louse infection is not harmful but can result in itching. This is due to an allergic reaction to the louse saliva, which is injected at feeding. Although sometimes the mere mention of head lice is enough to make a person’s head itch!
The number of head lice on an infected head can vary greatly, but the average number of adults is often quoted as 10. In some cases hundreds of lice can be found and recently there was a report of 2657 lice on one head!
The scientific name for a head louse is pediculus humanus capitis and a head louse infection is sometimes referred to as pediculosis.