What is seborrheic dermatitis?
The term “dermatitis” refers to an inflammatory condition of the skin. Seborrheic dermatitis is a type of chronic dermatitis that tends to affect the areas of the skin that produce excessive sebum (an oily substance). The sebum is produced by the sebaceous glands that are present within the skin. Some areas of the body are more oily than others. For example, the skin on the scalp, face, upper back and chest produces more sebum than the skin in other areas of the body. Consequently, these areas are most frequently affected by seborrheic dermatitis.
Why does seborrheic dermatitis occur?
The human skin is host to a variety of microorganisms. These microbes (also referred to as the skin flora) do not cause any disease under normal conditions because their numbers are kept in check by microbial competition and the body’s immune system. One of the components of the normal microbial flora on the human skin is a yeast (a type of single-celled fungus) called Malassezia.
In seborrheic dermatitis, there is an inflammatory immune response towards Malassezia yeast in the more oily regions of the skin. The exact reasons for such an inflammatory immune response towards Malassezia in the oily regions of the skin is not known. The population of Malassezia does not increase in the oily regions of the skin. Also, these yeasts do not penetrate the skin barrier to cause any infection.
In addition, there is no change in the composition of the sebum produced by the sebaceous glands. Therefore, these factors do not seem to contribute to the inflammatory skin reaction in seborrheic dermatitis. It is now suspected that Malassezia may not be the only contributing factor in the development of seborrheic dermatitis.
The skin affected by seborrheic dermatitis appears to have a scaly and greasy rash. The rash may have a yellow crust on top. Removing the flakes of the yellow crust reveals an underlying redness of the skin. Slightly raised plaques may also be present under the yellow crust in these skin areas. The affected skin areas are also relatively thicker than the normal skin due to an increase in the number of skin cells (keratinocytes).
The overgrown areas of the skin also contain fluid and immune cells. The skin around the hair follicles is most commonly affected. Seborrheic dermatitis is referred to by different names that depend on the area of the body that is affected. For example, seborrheic dermatitis of the scalp is often referred to as dandruff. In newborns, seborrheic dermatitis of the scalp is usually referred to as cradle cap. Seborrheic dermatitis may also be responsible for the diaper rash that is commonly seen in babies.
Signs and Symptoms
The signs and symptoms of seborrheic dermatitis develop slowly over a period of time. In the initial stages, the skin may begin to appear scaly and flaky. The yellow crust that is characteristic of seborrheic dermatitis may or may not be present on the affected skin areas. Red skin plaques may appear on the head, face, and chest areas in severe cases of seborrheic dermatitis.
The skin on the scalp becomes scaly and flaky. Small, white flakes of skin peel off and get entangled in the hair on the scalp. These white skin flakes are commonly referred to as dandruff. The affected skin areas on the scalp may also become itchy. Scaly skin may extend beyond the scalp, and affect areas of the neck, ears, and even the ear canals. Usually, seborrheic dermatitis occurs after puberty.
However, newborn babies are also susceptible to seborrheic dermatitis. The thick, yellow crust that appears on the scalp of babies affected by seborrheic dermatitis is commonly referred to as cradle cap. It is important to note that the scalp conditions seen in seborrheic dermatitis may also occur in other skin conditions (such as tinea capitis and scalp psoriasis).
Read more on cradle cap.
The face is usually affected only in severe cases of seborrheic dermatitis. In such cases, skin inflammation may affect the eyebrows, forehead, nose, and eyelids. Skin in these areas becomes scaly, and yellow crusts are also seen. The beard and mustache areas may also be affected.
Severe seborrheic dermatitis may affect different body areas. The regions of the body that usually get affected in such cases include the chest, axillae, scrotum, groin, and anogenital area. Swelling, redness, scaling, and yellow crust are typically seen in the affected skin areas.
Causes of Seborrheic Dermatitis
The exact cause of seborrheic dermatitis remains unknown. However, the following conditions are thought to play some role in the occurrence of seborrheic dermatitis.
As mentioned previously, the Malassezia yeast has been linked to the occurrence of seborrheic dermatitis. Treatment with antifungal medications improves the condition. However, Malassezia may only be a contributing factor rather than the cause of seborrheic dermatitis.
Parkinson’s patients seem to have a relatively higher incidence of seborrheic dermatitis. The subnormal dopamine levels in Parkinson’s disease may increase the production of sebum, making the skin more conducive to seborrheic dermatitis. Other neurological disorders are also frequently linked to seborrheic dermatitis.
Since seborrheic dermatitis tends to worsen in winters when the skin tends to be dry, it is suspected that increased sebum production may not be the mechanism for the development of this condition. A disruption of the normal barrier function of the skin may have a role to play.
Psychological stress is found to worsen seborrheic dermatitis. However, the underlying mechanism is not clear.
The likelihood of developing seborrheic dermatitis increases with the use of certain drugs, such as anabolic steroids, and drugs used to treat skin diseases, psychiatric illnesses, and autoimmune diseases.
The risk of developing seborrheic dermatitis has also been linked to a certain genetic factor.
People with immune system dysfunction (such as those with HIV/AIDS) are more likely to develop seborrheic dermatitis. It is thought that immune system dysfunction may contribute to the development of this condition by failing to keep Malassezia in check.
Treatment of Seborrheic Dermatitis
Seborrheic dermatitis is usually treated with topical medications such as ointments, lotions, creams and shampoos. These topical agents typically contain corticosteroids. Owing to the effectiveness of these topical medications, oral medications are only used in rare cases when the topical agents fail to control the disease. For babies, treatment of seborrheic dermatitis should be done only under medical supervision.