How do lice make your head itch?

Head lice cause intense itching of the scalp by their bites and their excrement.

1. Bites: Lice feed on human blood by biting the scalp, and their saliva contains an anticoagulant that prevents the blood from clotting. This can cause small, red, itchy bumps on the scalp.

2. Excrement: Lice excrete a substance called "nit glue" to attach their eggs (nits) to the hair shafts. This glue can irritate the skin and cause itching.

3. Allergic reaction: Some people develop an allergic reaction to lice bites, which can cause intense itching, swelling, and redness of the scalp.