You get an itchy rash, and it's not the first time. Maybe you're wondering if it's eczema or perhaps seborrheic dermatitis. Both are chronic skin problems that typically relapse, even after successful treatment. And doctors themselves can get these two causes of rash mixed up.
"They're both a kind of dermatitis," says Jason S. Reichenberg, associate program director and assistant professor of dermatology at the University of Texas Medical Branch-Austin. "They're both in the same chapter in the same book. There's no real sharp difference between the two." It's common for eczema—also known as atopic dermatitis—to be confused with seborrheic dermatitis or even psoriasis, according to an article published this year in the New England Journal of Medicine.
In fact, it's possible to have both seborrheic dermatitis and eczema at the same time. "Essentially, there's enough overlap that it's possible that many people have both," Reichenberg says. It could even be that there's just one underlying condition that manifests itself in two different ways, he says.
About 10 to 20 percent of people will develop atopic dermatitis, according to the American Academy of Dermatology. The condition often involves a dry, itchy rash on the face, hands, feet, inside of the elbows, and behind the knees. About 5 percent of the U.S. population has seborrheic dermatitis, which is referred to as "cradle cap" when it affects infants' scalps. It typically results in flaky, white or yellowish scales that form on oily parts of the body, such as the scalp, the inside of the external ear, or on the eyebrows, eyelids, creases of the nose, the lips, or along skin folds near the middle of the body.
A good first step for treating eczema is to try an over-the-counter hydrocortisone cream. In one study, about 80 percent of participants reported good, excellent, or clear improvement when taking topical corticosteroids such as hydrocortisone to treat their eczema, according to a 2005 study published in the N EJM . Your doctor may also prescribe a nonsteroidal ointment like the immunosuppressive medications Elidel (pimecrolimus) or Protopic (tacrolimus) instead. (Find out more about how to manage eczema.)
But treatment of seborrheic dermatitis is different. This inflammatory condition is believed to result from a "hypersensitivity to a yeast that likes larger oil glands," says Joseph Jorizzo, professor of dermatology and founding chair of dermatology at Wake Forest University. An antifungal solution, he says, is probably your best bet. A shampoo called Nizoral (ketoconazole), as well as creams, gels, foams, or shampoos that contain other antifungal ingredients, are considered mainstay treatments because they kill fungi, including yeasts. Putting these solutions on the scalp (where the problem is known as dandruff), ears, corner of the nose, and the chest can help manage the condition. If that fails to work, hydrocortisone can come in handy in treating seborrheic dermatitis in these areas as well, Jorizzo says. (Learn other tips for dealing with dandruff.)
For patients with seborrheic dermatitis, Jorizzo recommends using antifungal solutions regularly on problem areas because "that way you're in a prevention program, and you're only needing the hydrocortisone" when you experience a flare-up. How often you need to use the antifungal products can vary from daily to once or twice a week, experts say. Atopic dermatitis usually doesn't respond to the antifungal solutions that can help tame seborrheic dermatitis. Also, be cautious about using a hydrocortisone ointment or cream for an extended time because it can cause thinning of the skin and excessive hair growth, particularly at prescription-strength dosages.
If at-home treatments don't work, "there's a lot of very safe options that doctors can give you," Reichenberg says. Primary-care doctors may handle your treatment, or they may refer you to a dermatologist. Your doctor may prescribe stronger hydrocortisone creams or solutions, or he may prescribe Elidel or Protopic, which can be used to help treat eczema or seborrheic dermatitis. These steroid-free medications have antifungal and anti-inflammatory properties that can help tame both conditions, according to a 2006 article in the journal American Family Physician. But these medicines should be used for short-term treatment only; both have warnings on their labels that say that long-term safety is unknown and that a small number of people who took the medicines developed skin cancer or lymphoma.
In any case, if you've tried and failed in treating the problem on your own, it's important to see a doctor to rule out a more serious problem. "The real kicker is some people don't respond because they have something completely different," such as lupus, Jorizzo says. In those cases, the rash is a sign of an internal disease that needs a doctor's attention and treatment. A skin biopsy can be used to differentiate eczema or seborrheic dermatitis from more serious conditions like lupus.