Head lice information

Lice and nits

There are four hundred different species of lice in the world. Only three of these live on humans, including the coat louse and the pubic louse. And perhaps the best known of all: the head louse. Head lice are wingless insects of about two to four millimetres in size (about the size of a sesame seed and brown-grey in colour) that live as parasites on people’s hairy heads. Lice feed on human blood, on average 5 times a day. Without feeding on our blood they can only survive 8 to 24 hours. After that they dry out and die. A head louse is a parasite that lives exclusively on humans. A head louse cannot survive on an animal, so you cannot get or give a head louse through contact with animals. They reproduce by laying eggs (nits) that stick to the hair with a strong kind of ‘glue’.

Recurring problem

Head lice can be a nuisance and, especially in primary schools, they can be difficult to eradicate. Lice breathe through tiny air holes on their bodies called tracheae. Their bites often cause an itchy scalp and can even cause inflammation. Head lice prefer warm and dark places on the scalp, so you will find them mostly behind the ears, along the hairline and on the neck. The lice are not particularly dangerous and do not spread disease, but they are very annoying and contagious!

Is head lice only found on dirty hair?

It used to be thought that children with lice were dirty. Fortunately, that idea and the taboo surrounding head lice have largely disappeared, as it has nothing to do with personal hygiene. Some even suggest that head lice prefer very clean hair. But that doesn’t seem quite right either. The parasite has no clear preference for dirty or clean hair. So whether your hair is very greasy or spotless, the head louse can live in any hair.

Can head lice be prevented?

Prevention is of course better than cure. Is there such a thing as the best way to prevent head lice? Are there miracle cures for head lice? Unfortunately not. Immunity against head lice does not exist and the effect of preventive products has not been scientifically proven. Regularly checking is actually the only way to prevent head lice and their return. So don’t use expensive preventive products, they don’t work.

The RIVM has also withdrawn its advice for additional measures such as washing bedding, cuddly toys and clothing, etc., because there is no scientific evidence for the effects of head lice on the environment. There is no scientific evidence of the effectiveness of these measures.

If head lice are found, everyone in the household should be checked for head lice by combing their wet hair with a lice comb. Checking regularly and washing immediately with a good lice shampoo remains the best measure available. After one treatment with Licener Anti-Lice Shampoo the child can immediately return to school. However, it is important to report it to the school, sports club or childcare centre. They can then also check and thus prevent children from being infected again. Especially at school, it is important to check all children in a group at the same time. Moreover, the treatment of children with head lice should start on the same day. This prevents the lice from spreading. In addition, it is recommended to check the whole school class again two weeks later. Finally, children should avoid as much as possible direct head-to-head contact with friends during head lice infestation and right after a head lice treatment.

Life cycle

The eggs of the head louse are called nits. Not all the nits it produces are viable. The dead nits remain stuck halfway through the hair. The nits that are viable are always close to the scalp. That is usually behind the ears, under the fringes or in the neck, where the climate is optimal for the development of the nits: warm and not too dry. A nit is potentially viable when it meets all the following criteria.

  1. When the nit is attached to the hair at 1 cm or less from the scalp.
  2. When the blemish is firmly attached to the hair.
  3. When the spot is light to dark brown in colour.

The head louse develops in three phases: the neet (egg), the immature louse (nymph) and the adult louse (imago). The female louse attaches the nits to the hair with a glue-like substance, less than a millimetre above the scalp.

After no more than ten days, an immature louse crawls out of the egg and has no gender yet: a nymph. Nymphs usually lie flat on the scalp. In combing treatments, nymphs are therefore often missed because they slip through the teeth of the nits comb. Fortunately, this problem does not exist when treated with a good lice shampoo. This also kills all nymphs.

When a louse’s egg (the nit) hatches, it takes about seven to ten days for it to become an adult head louse. The total development from nits to adult lice takes about 3 weeks. Then reproduction begins. During her entire louse life, the female can lay about 80 to 100 eggs. So head lice spread easily and quickly.

How does the head louse spread?

The head louse spreads exclusively through hair-to-hair contact. The creatures cannot jump, fly or swim. They can only climb very quickly. The role of transmission via combs, hats, jackets, caps, scarves, headphones, cuddly toys and bedding has never been scientifically proven [Heukelbach et al., 2010; Speare et al. 2002; Speare et al. 2003]. The survival of the head louse depends on ambient temperature and humidity. Under normal conditions, an adult louse on a head remains alive for an average of 20 days. Separated from the human body, so without blood, an adult louse can survive at room temperature (20°C) for a maximum of 2 days. However, head lice found on things are usually dead, sick, old or infested and play a negligible role in infectivity [Maunder, 1983]. As long as living lice or unhatched nits are present on the head, a person remains potentially infectious.


It is best to check your hair regularly for head lice, preferably weekly.

If I have discovered lice, what then? Take the following steps:

  1. Check all family members.
  2. Treat family members who have head lice as soon as possible with, for example, Licener Anti-lice Shampoo – see how here!
  3. Tell people in the immediate neighbourhood that your child has head lice. Think of schools, day-care centres, (sports) clubs, grandparents, babysitters and the parents of friends.

Because head lice are contagious, we advise you to start the treatment with Licener anti-lice shampoo as soon as possible after detection. If any nits are still detected, it doesn’t necessarily mean that the person is still infected: even after treatment with Licener, a dead net can sometimes remain stuck in the hair. The glue with which nits are attached to the hair is very stubborn and does not dissolve by using Licener. A dead nit can therefore remain in the hair, but does not constitute a risk in terms of infectivity. Nits grow with the hair (about 1 cm per month), so the further away the nit is from the scalp shows when the egg was laid. Nits that are a few centimetres from the scalp are empty or dead nits.