Head lice are tiny wingless insects that live in hair. They are grey-brown in colour and about 2.5mm long, which is the size of a sesame seed, when fully grown. Head lice cling to hair and are usually found on or near to the scalp.
Lice themselves are not to be confused with nits – the empty egg cases from which they hatch. A nit (louse egg) is of a similar size to a small flake of dandruff.