Seborrheic Dermatitis is one of the most common skin conditions. It affects about 380 million people worldwide (5% of the population) and almost half of the population will experience some form of seborrheic dermatitis in their lifetime. The condition is considered a spectrum of diseases which range from dry, flaky, itchy scalp and may appear quite mild when only on the scalp but can be severe. In general, when only affecting the scalp with mild symptoms, it is considered dandruff. When the face and other parts of the body are affected, such as the ears or face, it is considered seborrheic dermatitis. Seborrheic dermatitis can also be present in the setting of psoriasis and described as “sebopsoraisis” where there is an overlap of both psoraisis and seborrheic dermatitis in the same person. Finally, in the most severe form of the disease, it may present as severe redness, scaling, and a rash that covers the entire body called erythroderma. Thankfully, this condition is extremely rare.
Seborrheic Dermatitis frequently affects the “seborrheic” areas of the body. These areas include sites of high sebum or natural body oil production including the scalp, outside and/or inside of the ears, face including beard or mustache areas, central chest, upper back, and sometimes the folds of the skin like the armpits or groin. There is usually redness with thickened yellow or white scales. Sometimes, the lesions can crack, bleed, and become painful especially when picked or scratched. Some internal diseases are related to severe seborrheic dermatitis which include HIV infection, a neurological condition called Parkinson’s disease, a lowered immune system such as those with the blood cancer called lymphoma or have received an organ transplant, and mood disorders like bipolar disorder.1,2 Many patients will also report that season changes including the transition to cold weather and stress typically flare up their skin.
The causes of seborrheic dermatitis are what we call “multifactorial” which basically means multiple factors are suspected to trigger the disease. Many individuals that suffer from seborrheic dermatitis have a family history of the condition. More recently, genes that play a role in the immune system or the way the skin naturally grows and sheds is different in people with the condition.3 Environmental factors also play an important role in causing seborrheic dermatitis. Normally, harmless yeast lives on the skin and hitch a ride our bodies never causing problems. In seborrheic dermatitis this yeast overgrows by feeding on the natural body oils. The specific oils produced by people who have seborrheic dermatitis may be slightly different, resulting in lower amounts of anti-inflammatory oils. The lower levels of anti-inflammatory oils result in an imbalance of the normal healthy skin bacteria and yeast. The yeast implicated in seborrheic dermatitis also produces an enzyme called lipase which turns healthy body oils into inflammatory irritating oils in people predisposed to the condition.4
Because this condition is so common, many treatments are available including over-the-counter options. Treatment does not cure the condition but can lead to much better control. If the lesions affect the scalp, then dandruff shampoos can be used. Many contain active ingredients such as coal tar, pyrithione zinc, and selenium sulfide. Additionally, a physician may prescribe prescription strength antifungal shampoos, skin steroids, antifungal creams, or anti-inflammatory non-steroidal creams such as tacrolimus for the condition. Overuse of steroids on the face may cause an acne-like eruption so regular application daily is discouraged. Oral antifungal medications have been shown to improve very severe seborrheic dermatitis which can sometimes be used in very difficult cases.5 Sunscreens are critical as sun exposure has been shown to flare up seborrheic dermatitis particularly during the transition from winter to spring. Finally, heavy alcohol intake (around 10 drinks per day) can lead to a variety of skin conditions one of which is seborrheic dermatitis so avoidance of alcohol may be important in some patients.6 Also, a full medical history is helpful to eliminate internal causes of seborrheic dermatitis including neurological conditions, chronic viral infections with HIV, and a lowered immune system. These causes of seborrheic dermatitis are extremely rare.