Buerger's disease occurs predominantly in men aged 20 to 40 who smoke cigarettes. More recently, however, a higher percentage of women (5%) and people over the age of 50 have been recognized to have this disease. Although the mechanism of the disease is unknown, the relationship of smoking to its occurrence and progression is apparent. There is no documentation of occurrence in nonsmokers, implicating cigarette smoking as the primary cause. Recent work suggests that Buerger's disease may be a reaction to tobacco of persons with a specific genetic type or an autoimmune disorder with immune cell sensitivity to some collagen types, which are constituents of blood vessels.