In Europe, whites are primarily affected. Prevalence is a way of measuring the number of people affected per 100,000 people in a given population. The prevalence figures for sarcoidosis are very unusual. In Europe, prevalence ranges from three in Poland, to 10 in France, to 64 in Sweden, to 200 for Irish women living in London. Furthermore, a person from a group with very low prevalence who leaves his or her native land for a second location with a higher prevalence will then have the same risk as anyone living in that second location.
Sarcoidosis affects both men and women, although women are more likely to have the disorder.
The average age for diagnosis is around 20-40 years. The cause of sarcoidosis is not known. One of the theories which has been put forth suggests that exposure to some toxic or infectious material starts up an immune response. For some reason, the body is unable to stop the response, and it spreads from the original organ to other organs. Because sarcoidosis has been noted to occur in family groups, a genetic cause has also been suggested.