An itchy, flaky scalp is a common skin complaint. Often it's just dandruff, but sometimes it can be a sign of a chronic health condition.

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Whether you first see the flakes on your bare shoulders or your black cashmere sweater, your reaction is probably one of horror: Dandruff! The unwanted scales are one of the most common skin conditions in the world. An estimated 50 million Americans deal with dandruff each year. Actually, "dandruff" is really just a layman's term for a flaky scalp. A dermatologist would call the condition seborrheic dermatitis or pityriasis capitis.

But sometimes the flakes and itchiness are due to another condition entirely: scalp psoriasis, which is a chronic inflammatory disorder. "It can be hard for patients to tell them apart because it's hard to inspect your own scalp," says Pooja Sodha, MD, assistant professor of dermatology at the George Washington School of Medicine and Health Sciences in Washington, DC. "And they both have similar symptoms of itching and scaling."

Here's a quick comparison to tell you what you need to know about common dandruff and scalp psoriasis: what causes these conditions, their symptoms, how they're treated, and when you should see a dermatologist.

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Credit: AdobeStock

What causes dandruff vs. psoriasis of the scalp?

There's disagreement among dermatologists about what causes dandruff. Some believe it's simply a buildup of the stratum corneum—the top layer of skin—that can occur if people don't wash their hair very frequently. "Seborrheic dermatitis might be a bigger issue for African Americans because of some hair care practices," explains Steve Feldman, MD, professor of dermatology at Wake Forest School of Medicine in North Carolina. "Because their hair would get dry if they shampooed very frequently, many African Americans use oils on their scalp and may only shampoo once a week or even less."

Another possible cause of dandruff may be overgrowth of a fungus—a type of yeast called Malassezia. "We all have various types of yeast on our scalp. It may be that some people's bodies have a reaction to that," says Dr. Feldman, who sits on the medical board of the National Psoriasis Foundation.

Or maybe you're having a reaction to a hair care product. "An itchy, dry, and flaky scalp could be telling you that you need to do a better job of rinsing the shampoo from your hair," says the American Academy of Dermatology (AAD). Leaving styling products on your scalp for too long without washing can also be irritating and lead to itching and flakes. AAD adds that some people may have an allergy to a shampoo, conditioner, or other product that touches the scalp.

Dermatologists say that many people may simply have a genetic predisposition to developing the condition. Dandruff is so common that "everyone will get dandruff eventually," says Cameron Rokhsar, MD, associate clinical professor of dermatology at Mount Sinai Hospital in New York City.

Unlike flakiness due to common dandruff, "scalp psoriasis is a chronic inflammatory condition that triggers the epidural cells to overproliferate," says Dr. Sodha. Dermatologists don't really know why the immune system sometimes becomes disregulated this way, but it's probably genetic. Scalp psoriasis affects fewer people than common dandruff. According to the National Psoriasis Foundation, it's estimated that half of the 7.5 million Americans with psoriasis have scalp psoriasis.

How do the signs and symptoms of dandruff and scalp psoriasis differ?

Per Mayo Clinic and AAD, dandruff may feel itchy, and the scalp may look red and be covered with white or yellowish scales that may look greasy. Dandruff often affects only the scalp and ears, though it can also affect the eyebrows, eyelids, and other oily parts of the body such as the forehead and the crease of the nose. It can also affect any part of the body with hair.

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Seborrheic Dermatitis
| Credit: Courtesy of DermNet NZ

The itching and scales of scalp psoriasis can sometimes look and feel almost identical to common dandruff, but there may be other clues. "Scalp psoriasis will often have other manifestations," says Dr. Feldman, who says that while it's possible to have psoriasis only on the scalp and nowhere else on the body, often there are symptoms elsewhere. "People might find changes in their finger- or toenails, or red, scaly spots on elbows, knees, or in the naval or gluteal cleft."

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Scalp Psoriasis
| Credit: Courtesy of DermNet NZ

While the differences may be subtle, dermatologists usually have no trouble making the diagnosis. The scalp scales of psoriasis are often thicker and drier than regular dandruff, and the flakes may look silvery and extend beyond the hairline.

How are dandruff and scalp psoriasis treated?

There's really no way to prevent either dandruff or scalp psoriasis, though if the itching and flaking persist, dermatologists can prescribe treatments and routines that will reduce flare-ups.

And while the two conditions are quite different, they actually share some treatments.

What to do about dandruff

Most cases of dandruff can be easily banished using an over-the-counter medicated shampoo, conditioner, lotion or foam, Mayo Clinic and AAD point out. There are several different ingredients that target the flakes, and you may need to experiment a bit to find which one works best for you.

"I like tar shampoos, which are good for decreasing inflammation," says Dr. Rokhsar, adding a caution that the tar may discolor blond or light hair. Another ingredient he likes is salicylic acid, "which is good for decreasing flakiness."

Dr. Sodha recommends zinc or selenium-based products, both antifungal. Ketaconozole is another antifungal ingredient in some over-the-counter anti-dandruff shampoos. "Use the product two to four times a week for a few weeks, and then if you see improvement or resolution, switch to once or twice a week for maintenance."

How to treat scalp psoriasis

Topical treatments like medicated shampoos are the first course of action for scalp psoriasis, too, and sometimes products with the same ingredients—such as salicylic acid and tar—are recommended, according to the National Psoriasis Foundation. "But scalp psoriasis may also be treated with topical steroids and vitamin D analogs, both available by prescription," says Dr. Feldman.

When to see a dermatologist

If you've tried over-the-counter solutions for several weeks, using them as directed, and your condition hasn't improved, it's probably time to see a doctor.

While common dandruff usually responds to special shampoos, scalp psoriasis may need more powerful treatments. In addition to the prescription topical medications mentioned above, doctors may recommend an oral medication or biologics, "especially if that person has extensive psoriasis elsewhere on the body, or is waking up feeling stiff in the morning [a sign of psoriatic arthritis]," says Dr. Feldman. "There's a perception that scalp psoriasis is resistant to treatment," he says, "but these products work."

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