**3. Epidemiology**

There is not reliable data regarding the incidence and prevalence of SS in general population. This relies on the fact that SS is an infrequent condition and the available data are based on series´ reports of and patient´s records from hospitals and dermatology departments. Moreover, it is necessary to take into account that the incidence of SS is determined by the incidence of infectious causes in general population (Hommel et al, 1993). With all these limitations, it has been reported that the incidence of SS in Scotland is 2.7 cases per million inhabitants and year (Kemmett & Hunter, 1990).

Gender distribution of SS is conditioned by the underlying or trigger disorder. There is a female predominance in parainflammatory and idiopathic cases which disappears in the infantile and paraneoplastic ones. There is no racial predilection.
