Head lice are tiny insects that live on the scalp and feed on human blood. They are about the size of a sesame seed and can be difficult to see. Head lice are most common among children, but anyone can get them. They spread easily through close contact, such as sharing hats or hairbrushes. The eggs of head lice, called nits, attach to hair strands and can be mistaken for dandruff. Infestations can cause itching and discomfort, but they do not transmit diseases. Treatment typically involves special shampoos or lotions designed to kill the lice and nits.