Grisly head lice facts

Approximately 7% of primary school children have them Most infestations involve only a dozen or so lice, but bad cases involve hundreds on one head - and extreme cases more than a thousand Most lice survive only approximately 10 days - an itchy head is a dangerous place A female louse lays between two and six eggs a time - louse population on the head generally double every seven days Lice are spread by head to head contact - lice tend to hang around in the hair by the ears for easy transfer The belief that lice tend to prefer clean hair is somewhat of a fallacy - they'll live anywhere there's blood

Rough estimates suggest that approximately 7% of primary school children have these unwanted visitors living in their hair.

They live by sucking blood from the scalp, and the female louse lays eggs attached to hairs.

It is these eggs, or nits, which the new shampoo claims to be able to highlight, reports New Scientist.

It works by bind a commercial organic dye to a protein called chitin found on the surface of the eggs - but not to the proteins on the scalp surface.

When an ultraviolet light is shone on the scalp, the dye glows, making it easier to spot any remaining nits missed by the nit comb.

The shampoo was described by its inventor, Professor Sydney Spiesel from Yale University School of Medicine, as "delightfully cheap and delightfully non-toxic."

Combing can remove eggs and lice

It may be attractive to parents unwilling to use treatments which use pesticides, for fear they may cause illness.

Dr Ian Burgess, from the Medical Entomology Centre - and independent consultancy near Cambridge, fears the desperation of parents to deal with the lice may mean the produce is successful, even if it does not work that well.

He said he had been involved in some testing of chemicals which worked in a similar way, but found they were binding to the scalp just as readily as to the egg cases.

"Empty egg cases tend to glow in ultraviolet light anyway," he said.

"The difficulty is not simply finding the cases, but getting rid of them. The reason that head lice cases are rising in the country is because they are becoming generally more resistant to treatments."

Using a nit comb, he said, could be effective, but only if used for half an hour a day - and probably for at least two or three weeks.

"There are significant numbers of people who are so desperate that they will buy this whether it works or not."

He said he would still recommend that a pesticide shampoo treatment was the first port of call for a parent trying to eradicate a head lice outbreak - and warned that instructions about repeating the treatment must be followed closely, or the insects would return stronger.