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This term refers to a scaly, crusting, and erythematous eruption that is most common in infancy (ages 2–12 weeks), where it tends to favor the scalp, diaper area, and intertriginous folds. Figure 9-1 is an illustration of the process in the scalp where it is often referred to as cradle cap. Figure 9-2 shows seborrheic dermatitis in the diaper area. The figures cannot convey the greasiness of the condition, and indeed, at certain stages dry scaling rather than oiliness is predominant. A subset of infants with seborrheic dermatitis will go on to develop atopic dermatitis and it sometimes may be difficult to differentiate between these two conditions. Some basic principles are that the lesions of seborrheic dermatitis are usually well circumscribed, do not itch, and localize toward the scalp and intertriginous areas. The greasy red-orange scaliness of seborrheic dermatitis is somewhat helpful in differentiating this disorder from atopic dermatitis. Finally, seborrheic dermatitis has its onset early in infancy and usually resolves by 1 year of age; atopic dermatitis tends to begin later in infancy and to be more persistent.
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Figure 9-3 shows seborrheic dermatitis in and around the axilla. Note the circumscribed salmon-colored lesions and the greasy character of the scale. Figure 9-4 shows a more extensive process that is nearly generalized and drier in scaly appearance. The cause of this very common condition remains unknown. Although it favors areas with an increased number of sebaceous glands, there is no evidence that seborrheic dermatitis is a disease of sebaceous glands or is related to excessive sebum production. Some studies have suggested that the lipid composition of sebum in seborrheic dermatitis may be abnormal. Bacteria and yeasts are often present in areas of involvement, but neither Candida albicans nor Pityrosporum ovale has been shown to be an etiologic agent.
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Seborrheic dermatitis, common during infancy, is relatively unusual during later childhood. It resurfaces as a problem during adolescence and then seems to become progressively more common through adult life. The generalized seborrheic dermatitis of infancy gives way to a process that primarily involves the scalp, forehead, tarsal margins of the eyelids (blepharitis), ears, and nasolabial folds. Itching or vague discomfort sometimes accompanies the low-grade inflammation. Flare-ups of the disease tend to occur during the spring and fall seasons. Pictured in Fig. 9-5 are erythema and greasy scaling of the forehead and eyebrows. Figure 9-6 illustrates typical involvement of the nasolabial folds. Seborrheic dermatitis is easily controlled but not everlastingly curable. Treatment may consist of the topical application of ketoconazole cream or a mild topical steroid. The frequent use of tar shampoos is particularly ...