Seborrheic dermatitis (SD) is a common skin disease, which is a chronic, recurrent, inflammatory disease. The incidence of SD in the population is 2%-5%, of which 70.3% occurs in the head, and is scalpseborrheic dermatitis (SSD), which can manifest as simple pityriasis (dandruff), inflammation, itching, and alopecia of the scalp. SD occurs during periods of active sebaceous glands, and its incidence peaks in three age groups—the first trimester of life, adolescence and adulthood, peaking between the ages of 40 and 60 years.
Adult seborrheic dermatitis is more common in seborrhea-rich parts of the scalp, eyebrows, nose, cheeks, chest, back, etc., which is characterized by scales at the base of erythema, which often appear yellow and greasy, and can be accompanied by varying degrees of itching.
- What are the causes of seborrheic dermatitis?
At present, the etiology and pathogenesis of SD are not fully understood, but they may be related to a combination of various exogenous factors, such as Malassezia infection, abnormal lipid secretion, immune factors, genetic factors, and skin barrier damage.
About the common sites of seborrheic dermatitis
(1) Head: The minor damage to the head is a small grayish-white chaff-like or greasy scaly patch with flushing at the base. Later, it gradually expands and merges into a large map-like patch with clear boundaries, and in severe cases, most of the scalp is covered with greasy thick scabs, which may ooze and have a fishy odor.
(2) Face: Facial lesions spread from the scalp. The forehead, eyelids, and nasolabial folds are heavy, and they are yellowish-red greasy scaly patches. The eyebrows and their surroundings are diffuse erythema covered with white scales, or yellow greasy pachyma, and the eyebrows may be sparse by scratching. Eyelid involvement is characterized by blepharitis, which is covered by small, red, white scales. The nasolabial folds and alar of the nose are mostly yellowish-red greasy patches. In addition to flaky, greasy, scaly erythema, skin lesions in the beard area of men are often accompanied by folliculitis. Erythema, swelling, and chapping may occur behind one or both ears. Seborrheic otitis externa is common in older patients.
(3) Trunk: Trunk skin lesions are more likely to occur between the chest and shoulder blades, initially small reddish-brown follicular papules with greasy scales, and later fused into round or irregular yellow-red or light red greasy patches, sometimes the center of the patches can be seen to recede and form annular or multi-ring lesions around the periphery. Pityriasis rosea lesions may also be present.