An illness is a medical problem that detracts from the good health of an individual. The most common kind of illness is a physical illness—a problem with the body, caused by any number of factors such as infection, or poisoning. Illness can also be psychological.
Author John A. Schindler, M.D. introduced the powerful concept of EII, or "emotionally induced illness," long before most physicians were aware of the connection between emotions and physical health. (1954)