Integration: Unifying Concept
Seborrheic dermatitis is recognizable clinically, not by virtue of study of the individual lesions that compose it, but by virtue of the distribution of those lesions. Sections of tissue of biopsy specimens taken of seborrheic dermatitis, however, show characteristic changes, namely, a superficial perivascular infiltrate of lymphocytes, dilated venules in the upper part of the dermis, slight acanthosis, focal spongiosis in both surface and infundibular epidermis, and scale-crusts that reside especially at lips of infundibular ostia. More longstanding lesions of seborrheic dermatitis, especially those situated over the sternum, show psoriasiform acanthosis and scant spongiosis, in addition to mounds of scale-crust.
Seborrheic dermatitis is a specific type of inflammatory process, distinct from psoriasis. Lesions referred to as sebopsoriasis or seborrhiasis, implying thereby a combination of two diseases, almost always represent either seborrheic dermatitis or psoriasis, not both of them.
The cause of seborrheic dermatitis is not known.