What causes seborrheic dermatitis?

May 1, 2005

What is the cause of seborrheic dermatitis?

Q. What is the cause of seborrheic dermatitis?

Remember that the nonreproductive form of the fungus is Pityrosporum ovale. Pityrosporum is converted to the reproductive growth phase known as Malassezia to cause disease. Malassezia furfur is the subtype that is thought to cause tinea versicolor and Malassezia globosa is the cause of seborrheic dermatitis. It is the digestion of sebum on the scalp by Malassezia globosa that releases free fatty acids causing inflammation and the accompanying proliferation. Seborrheic dermatitis is more common in elderly and debilitated patients due to decreased immune surveillance of fungal organisms and decreased hygiene.

A. There is a variety of OTC products that are designed to aid in the treatment of seborrheic dermatitis, besides antidandruff shampoos. These products fall into two categories: those containing salicylic acid and those containing 1 percent hydrocortisone. These are considered OTC drugs and as such will have the active agent listed separately on the packaging. There are no products that contain both ingredients in the same bottle, since the U.S. Food and Drug Administration (FDA) does not allow hydrocortisone in combination with any other active ingredient in OTC drugs.

The salicylic acid products may contain up to 3 percent salicylic acid in a volatile vehicle and are leave-on products designed for direct scalp application. The salicylic acid remains on the scalp until the subsequent shampooing to digest scalp skin scale functioning as a keratolytic. Salicylic acid is oil soluble and as such is effective in the sebum-rich scalp environment. This is important to remove the flaking component of seborrheic dermatitis, which is cosmetically unattractive. However, removal of the scalp scale is also necessary to prevent maceration and creation of an environment that encourages Malassezia globosa growth.

The 1 percent hydrocortisone liquids, on the other hand, function as anti-inflammatories. Their role is to decrease inflammation thereby also decreasing the proliferative component of seborrheic dermatitis. The decreased inflammation also improves the patient symptoms of itching, stinging and burning.

Q. Are there any OTC products helpful in treating seborrheic dermatitis?

A. The OTC salicylic acid and 1 percent hydrocortisone products can be effectively used in the treatment of mild seborrheic dermatitis. I prefer to use the active agents in combination with an antidandruff shampoo to deal with all of the aspects of seborrheic dermatitis.

The antidandruff shampoo used daily or every-other-day contains agents to destroy the Malassezia globosa population on the scalp. This is combined with application of the salicylic acid preparation to the scalp in the morning. The salicylic acid is a mild anti-inflammatory and potent keratolytic reducing scalp scaling. The 1 percent hydrocortisone liquid is applied in the evening to reduce inflammation and the symptoms of itching. Thus, this OTC combination therapy decreases the fungal count while minimizing both proliferation and inflammation. All aspects of the seborrheic disease cycle are addressed.

Q. Can the OTC products help in the maintenance phase of seborrheic dermatitis?

A. It is important to talk about the maintenance phase of seborrheic dermatitis, since this is a chronic disease. There is no cure because the Pityrosporum organisms are abundant in the air. It is only a matter of time until reinfection occurs in susceptible individuals. Treatment with prescription medications, if applicable, can be followed by maintenance with OTC products.

In the preceding discussion, I outlined a method for using OTC salicylic acid and 1 percent hydrocortisone products for the treatment of mild seborrheic dermatitis. This same treatment routine of using a salicylic acid liquid in the morning and a 1 percent hydrocortisone liquid in the evening can be used once or twice weekly for maintenance. The salicylic acid prevents the desquamating corneocytes from building up to produce visible flaking and the 1 percent hydrocortisone prevents initiation of the itch-scratch cycle, a dominant feature of seborrheic dermatitis.