BACKGROUND: Numerous factors have been implicated in the pathogenesis of rosacea, which remains obscure.OBJECTIVES: To examine the epidemiological characteristics of rosacea patients, the histopathological alterations, the prevalence of gastric Helicobacter pylori infection and the role of ultraviolet radiation, to detect the presence of Demodex folliculorum on affected skin and to elucidate the immunological nature of this disorder.METHODS: The study included 100 patients with rosacea. Each patient was assessed with a clinical, haematological, biochemical and histological examination; serology test for the detection of antibodies against H. pylori; direct immunofluorescence on perilesional, sun exposed skin and indirect immunofluorescence with monkey oesophagus as a substrate; antinuclear antibody titre and a skin surface biopsy to search for Demodex folliculorum.RESULTS: Women were more frequently affected. Half of our patients were 51-70 years old. About two-thirds were photo-types I and II and 73% complained of worsening of conditions after sun exposure. An almost permanent histopathological feature was solar elastosis. Higher prevalence of H. pylori was not established. Prevalence and mean density of Demodex folliculorum were significantly increased in rosacea patients. Direct and indirect immunofluorescence tests were positive in 6.4% and 6.7% respectively. Antinuclear antibody titres were found in 21.1%.CONCLUSIONS: Our results suggest the pivotal role of chronic sun exposure in the pathogenesis of rosacea. Demodex folliculorum represents a significant cofactor that may contribute to the transition of the disease from a vascular to an inflammatory stage. The low positive results of direct and indirect immunofluorescence do not support a potential autoimmune role in the development of rosacea.