Distribution: scalp, eyebrows, and other hairy areas, nasal folds, glabella, retroauricular folds, external os of the ear, and midsternum

Clinical Presentation

Seborrheic dermatitis is particularly likely to occur in areas where moisture is easily trapped. Thus it most often affects hairy regions and intertriginous folds. The most common of these areas are listed above under diagnostic hallmarks.

In hairy areas seborrheic dermatitis is characterized by the presence of diffuse, poorly marginated plaques of scaling erythema. The scale is often compacted against the underlying skin by the anchoring effect of the hair shafts. In such instances the scaliness will not be appreciated until the involved area is scraped with a fingernail. In very young infants, scale buildup may be extensive enough to deserve the colloquial term "cradle cap." When the scalp is involved, oiliness (seborrhea) of the scale may be noticeable, but in the other locations this is not a prominent finding. In men, seborrheic dermatitis sometimes occurs in the beard, mustache, and hairy area of the midsternum.

Evidence of epithelial disruption is usually not prominent. Pruritus is usually present, but few excoriations are found. Often the only clue to the presence of epithelial disruption is the yellow color of the overlying scale. This yellow color occurs because of small amounts of serum that have exuded onto the surface of the scale. Frank crusting, with less prominent scale formation, occurs in patients with more severe disease.

Seborrheic dermatitis of the scalp must be distinguished from tinea capitis and psoriasis. In these two latter diseases, sharply marginated individual plaques are found, rather than diffuse involvement. Notable hair loss occurs with tinea capitis, but this is not the case in psoriasis or seborrheic dermatitis. In both psoriasis and seborrheic dermatitis, extension onto the nonhairy, marginal skin surrounding the scalp is occasionally seen.

Seborrheic dermatitis also occurs on nonhairy (glabrous) skin. It is particularly likely to be found in the retroauricular folds, the external os of the ears, the nasal fold, and the glabella. Less commonly, intertriginous areas such as the inframammary and inguinal folds may be involved. Generally, seborrheic dermatitis in these areas can be considered as an eczematous variant of intertrigo.

The plaques of seborrheic dermatitis occurring on glabrous skin are often rather sharply marginated and for this reason are easily mistaken for papulosquamous lesions. Confusion with psoriasis is particularly likely, and the terms "seboriasis" and "sebopsoriasis" are sometimes used when differentiation is not possible.

Course and Prognosis

Seborrheic dermatitis is a chronic disease characterized by lnbations and remissions. It can occur at any age. In infancy it is frequently seen as "cradle cap" and as one form of diaper dermatitis . Seborrheic dermatitis is not very prominent during the childhood years, but it frequently develops in the early teens sat the onset of puberty.therafter, it can occur at any time throughout adult life.The acute onset of what appears to be severe seborrheic dermatitis of the face can occur as one of the manifestations of acquired immunodeficiency syndrome (AIDS).

Pathogenesis

The cause of seborrheic dermatitis is unknown. Its name is derived from the fact that it was first recognized in the scalp, where the flow of sebum (seborrhea) is prominent. Since seborrheic dermatitis occurs in many other areas unassociated will sebum production, this relationship is probably more coincidental than causal. Likewise, the relationship between simple dandruff and seborrheic dermatitis is not completely clear. It is true that all patients with seborrheic dermatitis of the scalp have dandruff in the sense that scale is present but a large portion of the population has dandruff, sometimes rather severely, without ever developing the inflammatory component of seborrheic dermatitis. Possibly the retention of sweat, with or without subsequent overgrowth of normally present pityrosporum sp. yeasts, is an initiating factor for the conversion of dandruff to seborrheic dermatitis.

Hygiene and environmental factors seem important. Seborrheic dermatitis of the scalp generally first appears or worsens when shampooing is not carried out on a regular basis. The converse is also true; frequent, vigorous shampooing (regardless of the type of soap used) is remarkably effective in keeping the disease under control. As mentioned above, perhaps the simple accumulation of scale, anchored in place by hair shafts, causes maceration and inflammation resulting from sweat retention. Support for this hypothesis is offered by the observation that when a man with no skin disease on the face grows a beard, he may then suddenly develop seborrheic dermatitis in that area.

Climate may also playa role. Seborrheic dermatitis regularly worsens in the fall and winter and improves considerably in the spring and summer. Additionally, the disease does seem to be more troublesome in tropical areas than it is in equally warm but dry desert areas.

Factors relating to the central nervous system are of considerable interest. Clinicians have long recognized that seborrheic dermatitis sometimes accompanies Parkinson's disease. Psychologic factors also seem important, since nearly all patients agree that their seborrheic dermatitis worsens appreciably during times of stress and fatigue.

Finally, recent evidence suggests that at least some forms of seborrheic dermatitis may be caused by overgrowth of the common Pityrosporum yeasts that inhabit normal hair follicles.

Therapy

The mainstay of therapy for seborrheic dermatitis of the scalp is frequent, vigorous shampooing. The type of shampoo applied seems much less important than the aggressiveness and frequency with which it is used. Shampooing ought to be done initially on a daily basis, thereafter, the intervals can be lengthened as tolerated. The fingernails should be used to mechanically loosen scale, and scrubbing ought to be carried out for at least several minutes. For mild to moderate seborrheic dermatitis, shampoos such as Sebulex, Head & Shoulders, Zincon, and Selsun Blue can be used. For more severe involvement, tar shampoos (Sebutone, Zetar, T/Gel), prescription strength (2.5%) selenium sulfide (Exsel, Selsun), or antiyeast shampoos such as ketoconazole (Nizoral) will be required. Recent reports also suggest that oral administration of ketoconazole (Nizoral) can be of help. In the more severe cases of seborrheic dermatitis, topical steroid lotions applied after shampooing may be required in order to bring itching and inflammation under control.

Perhaps surprisingly, attention to the scalp (even in the absence of scalp involvement) is important in the treatment of seborrheic dermatitis occurring elsewhere. Topical steroids such as 1 % hydrocortisone cream applied twice daily are, however, also necessary.