Addison's disease is an illness in which the adrenal glands stop producing hormones that are important for certain bodily functions. The most common cause of Addison's disease is an autoimmune disease. Some other possible causes of Addison's disease include chronic infection (mainly fungal infections), tuberculosis, and surgical removal of the adrenal glands. A few common symptoms of Addison's disease include diarrhea, nausea, weight loss, and loss of appetite. Some people with the disease may also experience darkening of the skin in both exposed and non-exposed parts of the body. Although Addison's disease cannot be cured, it can be treated and controlled with medication. In fact, most people with the disease should expect to lead healthy lives with a normal life expectancy.