Head lice are small, grey-brown, six-legged insects which feed on blood taken from the scalp, attaching themselves firmly to hair using specially adapted claws.

An adult can grow to 2-3mm (about the size of a sesame seed on a burger bun). They stay close to their food source on the skin and are often difficult to spot. They can’t jump, swim or fly, and only move from one person to another during close and persistent head-to-head contact.

Head lice only live on humans – so can’t be transferred from animals. And any which have fallen from a head will either be dead or dying – making it unlikely they could be caught from hats, towels, combs, carpets or bed linen.

It’s a common mistake to assume head lice can only thrive in dirty or unhygienic conditions. Having clean hair doesn’t provide any protection. Indeed there’s some evidence that they prefer well-groomed hair. So it’s unlikely that using shampoos and conditioners by themselves could prevent or remove head lice.

It’s widely believed that the number of people being infected with head lice has increased over recent years. But there’s little evidence to support this. The perception may simply be because people are less embarrassed to discuss the issue than they were some years back.

Reports that children pick up head lice soon after returning to school may be due to misdiagnosis. This is a common problem, especially after schools have sent out alert letters.