Sarcoidosis is an illness that causes tiny islands of inflammatory cells to form throughout the body. These microscopic groups of cells are called granulomas. They are especially common in the lungs, lymph nodes, skin, eyes and liver. The cause of sarcoidosis is unknown.
Sometimes, these granulomas cause very little damage, so a person with sarcoidosis does not have any symptoms of illness. In other cases, however, the granulomas produce large areas of inflammation and scarring that can interfere with an organ's normal functions. Although most people with sarcoidosis eventually recover, a few develop forms of the illness that are long-lasting (chronic) and get worse with time.
Sarcoidosis can affect almost any organ in the body. But the most common target is the lung.
Although doctors do not know the exact cause of sarcoidosis, there is strong evidence that the illness involves an abnormal immune reaction. For example, it is known that the granulomas contain cells from the immune system, particularly a type called helper-inducer T cells. Some experts believe that the abnormal immune reaction of sarcoidosis may be triggered by an infection. Others suspect that the illness may follow exposure to an allergen (allergy-producing agent) in the environment. In addition, genetic (inherited) factors probably play some role in increasing a person's risk of developing the illness.
In the United States, sarcoidosis affects African-Americans 3 to 4 times as often as white people. Other groups with a higher risk of developing sarcoidosis are Scandinavians, Irish, British and Japanese. In general, women are affected more often than men. About 75% of all those affected are younger than age 40.