Female head lice are up to 3.5 mm long, while the males are a little smaller. The wingless insects have clamp-like legs, with which they can firmly grip onto and move along the hairs. They are reddish to dark grey in colour. They are well-adapted to the temperature of the skin surface (ideally 27 °C to 30 °C) and live exclusively off blood, which they must draw several times a day. The females attach their eggs (nits), which are approximately 0.8 mm in size, very firmly to the hairline using an insoluble substance. The entire development cycle from egg to adult creature lasts around 3 weeks.
An infestation of head lice is very unpleasant. The saliva, which ends up in the scalp when the insects bite and draw blood, causes unpleasant itching. It often results in localised skin reactions, such as a rash or the development of wheals. When you scratch the irritated area, bacteria can often get into the wounds, which can lead to extensive eczema. Lice are usually transmitted via direct human contact or through communal use of hats, caps, towels, combs, hairbrushes, hand towels, beds and clothing, to name just a few examples.
If you have an infestation of head lice, you should take countermeasures immediately using products available from the pharmacy.