Associated Dermatoses and Triggering Factors in Psoriasis*

SUMMARY There is a wide range of morphological variation of psoriasis which is due to structural and functional regional differences of the skin surface; to the frequent combination of psoriasis with other dermatoses; to the action of various triggering factors and to the changes produced by treatment of the dermatosis. For the understanding and management of the resulting complex psoriasiform dermatoses, an appreciation of the existence of these factors is essential. The patch of psoriasis offers resistance to impetiginization and to super‐infection by dermatophytes. The coexistence of eczema and psoriasis in the same lesion is common and may pass unsuspected. The combination of atopic dermatitis and psoriasis in the same individual is rarely seen. There is good reason to believe that patients affected by keratotic (Norwegian) scabies are psoriatics. Pityriasis rubra pilairs is not rarely a complex dermatosis in a psoriatic patient. Some forms of palmo‐plantar and linear keratoses are of hidden psoriatic nature. Due to modern methods of therapy (corticosteroids and antimetabolites) the number of the complex, atypical forms of psoriasis is on the increase.