Adult head lice (or "louse" for just one) are approximately the size of a sesame seed and can vary in color from white to brown to dark gray.

Louse eggs (nits) are much smaller and look like light gray or brown ovals that are glued to individual hair shafts.

Head lice spread from one person to another through close bodily contact. Sometimes they spread when people share clothing or personal items such as hats or hairbrushes.