Psoriasis is a systemic disease that affects not only the skin but also various organs and systems of the body. The well-known theories of the psoriasis development (infectious, immune, genetic, metabolic, intoxication, neurogenic, endocrine) are described; special attention is drawn to psoriasis and atopy from the standpoint of their comorbidity. The analysis of data on the incidence of atopic diseases, in particular atopic dermatitis, in patients with psoriasis and psoriatic arthritis was carried out. The role of allergens as probable triggers of the inflammatory response in the psoriatic process is discussed. The data on the results of specific allergological examination of patients with psoriasis are presented. The similarities and differences of immunological processes, genetic determinants, and histological changes in psoriasis and atopic dermatitis are described. The data on changes in the cytokine orientation in psoriasis and atopic dermatitis are considered. Particular attention is drawn to the frequency of occurrence and features of contact allergic reactions in patients with psoriasis. It was determined that a long chronic course of the inflammatory process in psoriasis leads to damage to the epidermal barrier and, therefore, to a higher penetration of allergens/antigens through the foci of pathologically altered skin and can be considered as an additional element of the progression of the disease. In the literature, considerable attention is paid to the association of psoriasis with atopy; however, there is no consensus on the features of the spectrum of sensitization to allergens in patients with psoriasis that necessitates further study of the problem. Identification of common links in the pathogenesis of psoriasis and atopic dermatitis will improve understanding of the formation of inflammatory processes in the skin from the point of their comorbidity.