Head lice affecting the scalp (Pediculosis capitis) is a very common problem, especially in school children. There are various treatments, but whatever approach is used they can be a persistent or recurring nuisance.

The main symptom, if noticed by the individual, is an itchy scalp. This is sometimes especially so behind the ears.

The cause is a tiny insect which lives on the scalp, and feeds by sucking blood through the skin. The head louse grips on to the hair with its six tiny claws.

The female lays its eggs (nits) in sacs which are glued to a hair. These take seven to ten days to hatch. The lice then take seven to fourteen days to become mature and ready to reproduce. The total numbers of lice thus rise very quickly.

Head lice do not jump, fly, or swim. They spread by direct contact, "walking" from one hair or head to another. They happen in the best circles, and do not mean that you or your child are unclean or dirty, in fact some people say that head lice prefer clean heads.

About half of the children affected will notice itching of their scalps which draws attention to the problem. The lice themselves are small, about the length of a match head, and may be difficult to see, as their colour is often close to the hair colour.

Newly laid eggs are usually close to the scalp (about 1.5cm or about 0.5in) and as the hair grows this, and subsequently the empty sac, once it is hatched, will move further from the scalp.

When the egg is still in the sac it is small and rather dull in colour, and difficult to see. Once the egg has hatched, (7-10 days) the sac is white, and easier to see.

Head louse (Pediculus capitis) only affects humans, and cannot be passed on to, or caught from animals.

The best way to check on the presence of lice, if you are not sure, is to use the following lice detection regime:

1. Wash the hair as normal.
2. Apply conditioner liberally, including the full length of long hair.
3. Lay out white tissues over which you will comb the hair.
4. Comb the hair through with a normal comb first, to get rid of any knots.
5. With a fine tooth comb ("nit comb"), starting from the roots of the hairs, comb out along the complete length of the hair. After each stroke check the comb for lice and wipe it clean. Work systematically around the whole head of hair.
6. Rinse the hair as normal.

Firstly, don't panic! Most times you can make the diagnosis and start the treatment yourself, but if in doubt, or if the lice seem resistant to treatment, consult the pharmacist, nurse (attached to the school or the doctor's surgery), health visitor or doctor.

There are various proprietary, active treatments available, and so-called "bug-busting".

The chemical treatments fall into a number of groups:

• Pyrethrins
• Synthetic pyrethroids (permethrin and phenothrin)
• Organophosphates (malathion)
• Carbamates (carbaryl)
• Herbal

Of these, the one which best stands up to scientific scrutiny is permethrin 1% creme rinse, but the lice can become resistant to any of the treatments, and if a correctly applied treatment does not work, it is wise to use an alternative on the subsequent occasion. You should not use a different formulation of the same chemical.

The normal advice is to treat once, and repeat seven days later. On each occasion it is important to make sure the application gets to all the hair, and it is worth combing through the hair with a fine tooth comb, over tissue paper, after 20 minutes.

By this time the lice should be coming out dead (not moving) and this helps to confirm the effectiveness of the treatment. If live, mobile lice are found at this stage, they are resistant to that treatment, and an alternative is likely to do better.

The treatment does not kill the eggs, and the second treatment is because any remaining eggs should have hatched, and the young lice should thus be killed. If lice are found after the second treatment it is wise either to repeat the treatment after another week, or at least to check the hair again, as above, using conditioner.

There is no need to wash or specially treat clothing or bedding that has been in contact with head lice. They need warmth to survive and within hours of leaving their host they dry out and become unable to reproduce.

Treatments all have the potential for unwanted side effects, and you should discuss the pros and cons with the pharmacist, nurse or doctor. In addition to unwanted side effects there is an increasing problem with lice which are resistant to the effects of the treatments.

Bug-busting

This is currently the treatment recommended by the English Department of Health. It can be very effective, but is not yet supported by published scientific evidence.

"Bug-busting" consists of the approach listed above for detection of lice, repeated at regular intervals.

1. Wash the hair as normal.
2. Apply conditioner liberally, including the full length of long hair.
3. Lay out white tissues over which you will comb the hair.
4. Comb the hair through with a normal comb first, to get rid of any knots.
5. With a fine tooth comb ("nit comb"), starting from the roots of the hairs, comb out along the complete length of the hair. After each stroke check the comb for lice and wipe it clean. Work systematically around the whole head of hair. Continue for at least 30 minutes.
6. Rinse the hair as normal.
7. Repeat every two to four days for at least two weeks.

The conditioner causes the louse to lose its grip on the slippery hair, and also probably blocks the breathing apparatus (spiracle). This treatment has the benefit of not exposing the person to unnecessary chemicals, and reduces the likelihood of the lice becoming resistant to medications.

It is probably worth checking your child for lice weekly, and undertaking treatment if any are found.