Abstract: Rosacea is a common chronic inflammatory skin disease that predominantly affects the central regions of the face.Its pathogenesis remains unknown,and microorganisms are considered to play an important role in its development.Demodex mites contribute a lot to the development of rosacea,probably through type Ⅳ immunological reaction.Bacillus olemnius and Staphylococcus epidermidis,which are found to be carried by Demodex mites,may synergistically collaborate with Demodex mites in the pathogenesis of rosacea.Besides,Helicobacter pylod and small intestinal bacterial overgrowth may be involved in the initiation of rosacea complicated by digestive tract symptoms,but the correlation and mechanisms remain unclear.There has been no evidence for the correlation between rosacea and Propionibactedum acnes or Wolbachia.