Craig Kakuda, age 13, of San Diego, Calif., for his question:

WHAT CAUSES AN ITCH?

An itch is the sensation caused by irritation of particular nerves in the skin. Nerve fibers have special endings that are tiny organs able to receive messages. Some nerve endings receive pressure sensations, some receive temperature reports and some receive pain signals. Stimulation of pain nerves in the skin sometimes results in itching.

A number of different causes can produce itching. One of the common causes is some chemical that touches the skin and irritates it, such as poison oak or ivy. Itching often results from infections. An allergy may also release chemicals that make the skin swell and itch. This brings a condition which is called hives.

Cool, moist applications usually soothe itching.