Biopsies from 108 patients with rosacea have been examined and the histological changes correlated with the clinical condition. There is no single histological feature unique to rosacea but it is characterized by a combination of several histological signs; various types of rosacea represent an exaggeration of one or another aspect of the basic pathological changes; the disease is neither primarily a folliculitis nor an inflammatory disorder of small blood vessels. There is disorganization of the upper dermal connective tissue with edema, disruption of fibers, and frequently severe elastosis. A comparison of 39 rosacea patients with 39 controls for solar elastotic change indicated an increased incidence and degree of elastosis in rosacea patients. It is suggested that loss of integrity of upper dermal connective tissue may permit vascular dilatation and that this may have an important role in the pathogenesis of the disease.
Marks R, Harcourt-Webster JN. Histopathology of Rosacea. Arch Dermatol. 1969;100(6):683-691. doi:10.1001/archderm.1969.01610300033005