Rosacea is a chronic cutaneous disorder characterized by centrofacial persisting erythema, telangiectases, papules, pustules, edema, phymas and ocular involvement. Despite being one of the most common skin disorders, its pathogenesis remains unclear and controversial. Although the disease triggering factors are well recognized, the underlying causes of rosacea have not yet been identified. Several different postulates about its pathogenesis can be found in the medical literature. Abnormalities of the pilosebaceous unit, as well as genetic, vascular, inflammatory, environmental and microbial factors have been described. The microorganisms that have been associated include Helicobacter pylori, Demodex folliculorum, Staphylococcus epidermidis, and Chlamydia pneumonia; all the studies have been inconclusive. We review currently available scientific data on the potential pathogenetic role of microorganisms in the development of rosacea.