Seborrheic dermatitis is a common problem of unknown etiology. Approximately 1 to 3 percent of adults have seborrheic dermatitis. The term is derived from the distribution of this disorder, in which erythematous, scaly patches develop in areas that are rich in sebaceous glands, such as the scalp, face, and upper trunk. The term "seborrhea" refers to excess oil secretion, although this finding is not uniformly present in patients with seborrheic dermatitis.
In infants, seborrheic dermatitis of the scalp is often called "cradle cap."
Pathogenesis of Seborrheic Dermatitis
The cause of seborrheic dermatitis is not completely understood. Evidence supports a causal role of the skin saprophytic species of Malassezia (formerly pityrosporum ovale), which has been shown to colonize the skin of patients with this disorder. A host reaction to Malassezia yeasts or their metabolites is thought to contribute to the inflammatory response seen in seborrheic dermatitis.
Malassezia are lipid-dependent organisms which proliferate in sebum and are normal residents of the skin flora. Although increased numbers of yeasts have been reported in patients with seborrheic dermatitis, the number of Malassezia organisms present on the skin does not always correlate with the presence or severity of the disorder. However, a contribution of Malassezia to the pathogenesis of seborrheic dermatitis is supported by the clinical response to antifungal therapies.
Clinical Manifestations of Seborrheic Dermatitis
Seborrheic dermatitis is characterized by erythema and scale, with some pruritus. The margins are usually less sharply demarcated in seborrheic dermatitis than in psoriasis.
The distribution is characteristic:
- lateral sides of the nose and the nasolabial folds,
- eyebrows and glabella, and scalp);
- less commonly involved are the chest, upper back, and axillae.
Dandruff of the scalp is a mild form of seborrheic dermatitis with minimal inflammation. Seborrheic dermatitis tends to be worse under mustaches and beards in men (shaving can be helpful in management).
Diagnosis of Seborrheic Dermatitis
The diagnosis of seborrheic dermatitis is usually made by physical examination alone. The differential diagnosis of seborrheic dermatitis varies by location. On the scalp it should be differentiated from psoriasis, atopic dermatitis, and impetigo; on the face, rosacea, contact dermatitis, psoriasis, and impetigo; on the trunk, pityriasis versicolor and pityriasis rosea.
When biopsy is performed, histologic features include mounds of parakeratotic scale around hair follicles and a mild superficial inflammatory cell infiltrate of lymphocytes. Stains with Periodic Acid Schiff or Gomori Methenamine Silver frequently reveal increased numbers of Malassezia furfur spores in the stratum corneum.
Treatment of Seborrheic Dermatitis
1) Dandruff (seborrheic dermatitis of the scalp)
Daily shampooing of the scalp with a medicated shampoo helps control scaling and pruritus. For best results, the shampoo should be left in place for a few minutes before rinsing. Antiproliferative and antimicrobial shampoos are both available.
Examples of antiproliferative shampoos include:
- tar (Z-Tar, Pentrax, DHS tar, Ionil T plus, T-Gel extra),
- selenium sulfide (Selsun and Exelderm),
- and zinc pyrithione (Head and Shoulders, Zincon, and DHS zinc).
Shampoos containing the antifungal agents ketoconazole or ciclopirox are effective in the control of scalp seborrheic dermatitis. One study compared the use of ketoconazole 2 percent shampoo with selenium sulfide 2.5 percent shampoo in patients with seborrheic dermatitis. Both were significantly better than placebo and similarly effective for reducing irritation and itching; ketoconazole shampoo was better tolerated. A large randomized trial found that ciclopirox shampoo was superior to placebo.
Tea tree oil (Melaleuca oil) from an Australian tree has been used as a "natural" remedy for dandruff. A trial that randomly assigned 126 people aged 14 or older with dandruff to four weeks of tea tree oil 5 percent shampoo or placebo found tea tree oil was significantly better. However, only one patient in each group achieved a complete response. There were no significant adverse events in this study; however, products containing tea tree oil have been associated with cutaneous allergic reactions, and tea tree oil may have estrogenic and antiandrogenic effects. At this point, the role of tea tree oil in the treatment of dandruff is uncertain.
2) Non-scalp seborrheic dermatitis
Topical corticosteroids, antifungals, or combinations of the two are the standard treatments for seborrheic dermatitis.
Low potency corticosteroids (class VI or VII) are used daily until improvement is seen, then tapered (table 1A-B). Creams or lotions are best tolerated on the face; on the scalp, alcohol-based solutions, gel, or foam preparations are effective.
Topical and systemic antifungal agents are also effective. Ketoconazole shampoo is approved for this indication, and benefit has been shown with ketoconazole cream, ciclopirox cream, and oral terbinafine.
Small randomized trials have come to opposite conclusions about the effectiveness of metronidazole gel compared with placebo. One small randomized trial found that metronidazole 0.75 percent gel and ketoconazole 2 percent cream had similar efficacy, however this trial was too small to demonstrate true equivalence. The role of metronidazole in the therapy of seborrheic dermatitis is uncertain.
A short-term randomized trial found that topical pimecrolimus (1 percent cream twice daily) was more effective than placebo in patients with moderate-to-severe facial seborrheic dermatitis. The study did not compare pimecrolimus to other active therapies.
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