Immunotoxicity is harm occurring to the immune system caused by exposure to chemical substances. Testing for immunotoxicity is a standard part of developing substances as potential new medicines. Symptoms of immunotoxicity can include increased rates or severity of infectious diseases or cancer. Toxic agents can also cause autoimmune diseases, in which healthy tissue is attacked by the body’s own immune system. Allergy is another form of immunotoxicity, and many chemicals are known to induce allergic reactions in some people.