Tissue - A group or layer of cells that together perform a specific function. Toxin - Poisons produced by certain animals, plants or bacteria. Tumor - An abnormal growth of cells or tissues. Substances found in abnormal amounts in the blood, in other body fluids, or in tumor tissue of some patients with certain types of cancer. Ultraviolet radiation - Invisible rays that are part of the energy that comes from the sun.
Ultraviolet radiation can burn the skin and cause skin cancer.
Skin specialists recommend that people use sunscreens that block both kinds of radiation. White blood cells - Cells that help the body fight infection and disease.