Headlice insecticide products work by over stimulating the louse's nervous system, causing paralysis and death.

Headlice resistance to insecticide products has been reported - although this is more likely to occur when a child has been repeatedly treated with these products over a considerable period of time. It appears that some lice survive that have a natural resistance to the chemical being used..

- and these survivors continue to breed and so create a personalised lice population that is resistant to a particular chemical. This may mean switching to another insecticide product or using other techniques.

Natural products claim to "remove", "combat" and "control" headlice rather than kill them. They work by stunning the lice, and it's important the hair is dowsed in product for at least an hour and combed immediately.

How effective are the headlice treatments?

Insecticide headlice treatments are likely to be the most effective and there is considerable research evidence to back this up. We asked the makers of natural products to provide us with evidence to support their claims. Much of the literature cited the same studies and some were performed on insects other than headlice or body lice (these insects were a similar size to lice). Other material provided was unpublished, so it was difficult for our researchers to comment on the methods used.

A study published in the New Scientist concluded that the use of alternative therapies, such as electric nit combs and essential oils, have yet to be proven in clinical trials.

There's been much debate about the effectiveness of "bug-busting" - which combines wet combing with hair conditioner. A recent article in the British Medical Journal suggests that bug-busting with this combination was four times more effective than two courses of insecticide treatment. But this contradicted a previous study in Wales in which malathion headlice treatment was twice as effective as a bug-busting regime.

One of the possible explanations put forward for the higher cure rate of bug-busting was improvements to the fine-tooth comb. But a new study which looked at using a permethrin creme rinse (with and without combing) found permethrin without combing was marginally more effective.

But no headlice treatment - neither chemical nor "natural" - is guaranteed to be completely effective. That's because none of them has been shown to kill all lice eggs. So a follow-up treatment is recommended seven to 10 days after the first application to break the egg/lice cycle.
From the far side

We found studies that tested the bizarre.

One study tested six "home remedies" - vinegar, isopropyl alcohol, olive oil, mayonnaise, butter, and petroleum jelly (all which claim to work by smothering the lice). The aim was to see how effective they were in eradicating lice and eggs. The study concluded that petroleum jelly worked the best - but none of the home remedies killed all lice and eggs within 24 hours. The same study also found that lice are almost impossible to drown: they emerged, unharmed, after eight hours underwater.

What parents say about headlice treatments

We've been inundated with responses from parents about how to deal with headlice - and many complain about the small fortune they spent on remedies from the chemist, only to find they didn't work. Combing proved to be the most effective technique: it works best if administered with a fine-toothed metal nit-comb. Many parents recommended a two-pronged attack involving regular combing and either ordinary hair conditioner (which stuns lice for 20 minutes) or a nit treatment from the chemist.

Some parents couldn't speak highly enough of the Robi Comb - a battery powered comb that can be used on dry hair and "beeps" when lice or eggs get caught in the teeth. Others found it a waste of time - particularly as it doesn't kill eggs.

Some parents advised dousing the hair in mousse and hairspray, which made it difficult for the lice to stick to the child's hair. Several suggested putting tea tree oil in the family shampoo, as a preventive measure - although there is little evidence to suggest that such treatment works.

Many parents were frustrated at their school's inability to deal with the problem, and some suggested schools should once again start running daily nit checks. But studies we found have shown a "no nit" policy at schools is not effective at eradicating headlice. Less than 20 percent of school children with nits will go on to develop infestations in 14 days; and about half of the children who are sent home with headlice don't have them.

We think schools should take steps to advise parents if an outbreak of headlice is found at a school.