Evidence from prehistoric burials shows that head lice have been with us since the dawn of human evolution. They’ve been found on the mummified remains of 4000 year-old pharaohs from ancient Egypt. And excavations of 1200 year-old Viking settlements here in the UK have unearthed nit combs made from animal bone.

Head lice don’t cause disease. But scratching their bites can lead to secondary infections. The term ‘lousy’ reflects the run-down feeling often caused by these infections. Previous generations would have used herbal remedies – such as rubbing rosemary or vinegar into the scalp.

None of these treatments would have been completely effective. But with the development of synthetic insecticides in the 1930s, we were armed with a far more potent anti-lice weapon. These powerful chemicals were soon being used throughout Europe and the United States to treat head lice.

There’s no doubt that these insecticides destroy head lice. But they don’t always penetrate the eggs. Which means that the problem reappears as soon as the eggs hatch. Leading to higher and more regular doses of insecticide.

We’re now realising that these insecticides can have very damaging side-effects. Particularly when used on children. Which is why treatments sold as ‘natural’ and ‘non-chemical’ are appearing in ever-increasing numbers in our shops and high street chemists.