Hair loss is a common side effect of chemotherapy and radiation therapy. It occurs because these treatments affect normal cells that grow quickly as well as cancer cells. Hair loss can vary from thinning to complete loss. It may occur quickly over a few weeks or slowly over months. Loss of hair can happen only in the area treated (such as radiation therapy) or all over the body, including the head, legs, arms, eyelashes, and pubic area. Talk with your doctor if there are choices that may reduce your risk of losing your hair, such as a scalp cooling cap. Not all types of chemotherapy and radiation therapy cause hair loss, but if it does happen, these tips can help.