It's a very distressing condition for parents and children, but one that doesn't particularly interest doctors. It's also something that hasn't overly excited the pharmaceuticals, although the conventional over-the-counter remedies that have been formulated bear all their usual fingerprints.

Your friendly pharmacist is likely to suggest a malathion-based product, which is an organophosphate pesticide used in sheep dip. Common side-effects include headache, nausea, paralysis, chest pain, muscular twitch, blurred vision, cramps, giddiness, impaired memory and disorientation, dizziness and hallucinations, but these tend to occur to farmworkers in regular contact with the dip.

It may well be that your child's exposure to malathion will be too slight for him to suffer any of these effects, but it's an area that has never been properly regulated, so nobody can be sure. If you are a brave soul prepared to take the risk, you need to know that malathion products are becoming less effective. A study last year discovered that lice are building resistance to organochlorine- and organophosphate-based insecticides such as malathion.

Safer conventional products, based on pyrethroids and permethrins, also quickly lose their effectiveness.

Because of the ineffectiveness of conventional treatments, many exasperated parents turn to alternatives; the treatment of head lice has garnered more anecdotal stories of wonderful home-made concoctions than almost any other condition.

Just as nobody has bothered to analyse the effectiveness of conventional treatments, the same can be said of most alternative remedies, although many parents have their own special solution that they swear by.

Favourite essences that the lice find unpleasant include citrus, lavendar, eucalyptus, tea tree and rosemary oils, although one reader found that aloe vera jelly was very effective.

Of the few natural remedies to be tested, those based on an extract of the yucca plant have been found to be effective. These products quite literally suffocate the lice. Yucca makes water molecules clump together, so blocking the airways of the louse and effectively drowning it.

Neem-based products have also been found to be effective in trials. One trial found it to be the most effective natural pesticide of them all, and was almost as powerful as malathion but without the potential side-effects.

But that's only half the story. Lice lay five to six eggs a day. These eggs, or nits, have to be removed, and the only way to do it is by hand-or more exactly with the aid of a metal nit-comb, a magnifying glass and a bright light.