Rosacea is a chronic, inflammatory facial skin condition occurring in adults and is characterized by periods of exacerbation and remission (1). The primary symptom of rosacea is persistent erythema, which with the secondary formation of telangiectasia and papules and pustules in the later stages of the disease becomes a permanent condition (2). It is a very common dermatosis which, according to the epidemiological data, occurs in the range from 2% in Germany to 10% in Sweden (3). A prevalent type of rosacea is an erythematotelangiectatic rosacea occurring in 81% of dermatology clinic patients (4). The etiopathogenesis of rosacea is still unknown but according to numerous hypotheses, it is determined by vascular disorders, immune disorders, degeneration of the connective tissue elements, pilosebaceous follicles disorders, as well as climatic, chemicals and dietary factors. Infection related etiopathogenesis becomes more popular. This is supported by an effective form of therapy aimed at unspecified microorganism (2, 5).

Demodex folliculorum is an arachnid belonging to the order of mites (6). They are obligatorily bound to their hosts. Various species of Demodex folliculorum may occur on different parts of the skin of a single host (7). Two species of Demodex are typical to human, namely Demodex folliculorum and Demodex brevis (6). The former is of an elongated shape and its length ranges from 0.3 to 0.4 mm. It resides in hair follicles. The latter and the smaller one measures from 0.2 to 0.3 mm. It is typically spindle-shaped with shorter legs and is usually found in sebaceous glands of the entire body or in Meibomian gland (8). Due to its inconvenient location, Demodex brevis is difficult to pull out and its role in the pathogenesis of skin diseases is not fully known (9). Demodex folliculorum outnumbers Demodex brevis, hoverer the latter inhabits a larger area. Regardless of its development phase, Demodex mainly feeds on skin cells and the components of sebum, which explains why it resides in the seborrheic areas including nose, cheeks, forehead and chin. In terms of anatomy, Demodex is composed of gnathosoma with oral aparatus and podosma and opithosoma (10). Gnathosoma comprises the chelicerae used to suck food and pedipalps, which are used to hold the food. Prosoma has four pair of legs (10). All the Demodex mites avoid sunlight. They leave their initial location and emerge to the skin surface only at night to mate. The life cycle of Demodex lasts from 14 to 18 days (7, 11). Transmission of Demodex from human to human occurs during direct contact (common toiletries, towels or dust) and increases with age. According to the literature, the proportion of colonised patients ranges from 20 to 80% with the peak between second and sixth decade of life (12). The authors assume that increased infestation of facial skin with Demodex folliculorum may contribute to the development of the symptoms. Forton et al. proved that an average density of Demodex in the facial skin equals 10.8 mites per cm² (papulopustular type), and 0.7 mites per cm² in the group of healthy people. Diagnosing the Demodex mites include skin scrapings or standardized skin surface biopsy (SSSB). The pathogenic role of Demodex is still a starting point for further experimental research on their role in the direct and indirect induction of local inflammation.

The main objective of this article is to present the current state of knowledge on Demodex folliculorum and their correlation to the pathogenesis of rosacea, based on the literature review and modified standardized skin surface biopsy in patients diagnosed with rosacea.