Ulceration: The development of a lesion of the skin or a mucous membrane such as the one lining the stomach or duodenum that is accompanied by formation of pus and necrosis of surrounding tissue, usually resulting from inflammation or ischemia.

Ultrasound: A procedure using sound waves that allows physicians and patients to get an inside view of soft tissues and body cavities, without using invasive techniques. It is most commonly used during pregnancy to view the fetus.

Ultraviolet (UV) radiation: Invisible rays from the sun. UV radiation can burn the skin and cause melanoma and other types of skin cancer. UV radiation that reaches the earth's surface is made up of two types of rays: UVA and UVB. UVA rays pass deeper into the skin and UVB rays are more likely to cause sunburn. Both kinds of radiation are believed to cause skin cancer and cause premature aging of the skin. People should use sunscreens that block or absorb both kinds of UV radiation.

UPCI Clinical Trials: University of Pittsburgh Cancer Institute. Clinical trials are designed to help health care professionals test new approaches to the diagnosis, treatment, or prevention of cancer.

UV-A rays: Rays of the sun that maintain a relatively constant intensity throughout the year and contribute to premature aging and wrinkling of the skin, sunburn, and skin cancer.

UV-B rays: Rays of the sun that are more intense in summer months, at higher altitudes, and closer to the equator.

UV-C rays: The strongest and most dangerous of the sun's rays that are normally filtered by the ozone layer.

UV index: A daily measure of the strength of the sun's ultraviolet (UV) rays for a region.