Head lice bites are neither painful or harmful. The greatest health risk posed by lice is from secondary infection. This often occurs when severe scratching has broken the skin – allowing head lice droppings and germs to enter the wound.

Skin irritation and scratching are often the first signs that someone has lice. This is the body’s allergic reaction to lice saliva as they feed from a bite. But these symptoms only occur in about one in three cases. And then only after about two or three months.

Other typical signs of head lice are a rash on the back of the neck, dark specks or smudging on a pillow or collar (caused by head lice droppings). Or nits found stuck to hairs which have fallen out, or been caught on a comb.

A thorough check of the hair in good light is the only way to discover if head lice are present. Lice will move quickly away to hide from prying fingers. So the most likely evidence will be nits attached to hairs.

Lice can lay their eggs anywhere on the head. But they are often found behind the ears and on the nape of the neck. Any nits found close to the scalp indicate that adults will probably be present. But if they’re only found further along the hair, the lice may have gone.

Hair grows at a rate of around 1cm a month, so the further along the hair any nits are found, the longer it could have been since they were laid. Which means a nit 2cm from the scalp could have been laid about two months ago. And with an average life span of 30 days, these lice could have hatched and died some weeks ago.