Chapter 207 Seborrheic Dermatitis
Diagnostic Summary
• Branny or greasy scaling over erythematous skin patterned on the sebum-rich areas of the scalp, face, and trunk. Facial areas include the forehead, eyebrows, eyelashes, nasolabial folds, and beard. Truncal involvement includes the presternal region, umbilicus, axillae, inframammary and inguinal folds, and perineum.
• The scalp appearance varies from mild, patchy dandruff to widespread, thick, adherent crusts; it may involve the anterior and posterior hairline and the periauricular skin. In infants it occurs as “cradle cap.”
• Usually nonpruritic, although active phases can manifest with burning and itching.
General Considerations
Malassezia yeast organisms are probably not the cause but a cofactor linked to depressed helper T cells (seborrheic dermatitis is very common in AIDS); increased natural killer cells, which increase inflammatory cytokines; increased sebum levels; activation of the alternate complement pathway; and genetic susceptibility to a skin barrier dysfunction.1 Malassezia species have lipase activity, which releases inflammatory arachidonic acid. Seborrheic dermatitis is aggravated by changes in humidity, scratching, emotional stress, diet, various medications, and androgen excess.