Dandruff is one skin issue many of us are quick to self-diagnose. Not just because the symptoms seem obvious, but because we’re frequently hit with marketing for the latest, greatest treatment options, so the condition is generally top of mind. Itchy scalp keeping you up at night? Must be dandruff! Little white spots on the shoulders of your sweater? Add dandruff shampoo to the shopping list! We’re less likely to stop and consider whether the root cause of those flakes might be scalp psoriasis, which can look similar but be more stubborn and difficult to treat.
While both conditions involve itchiness and flakes, their causes differ. Psoriasis is a chronic condition characterized by an overactive immune response that leads to excessive skin cell growth, creating thick patches called plaques. These can become severely itchy or even painful, and often require prescription treatments. Dandruff, on the other hand, arises from an overgrowth of a yeast called malassezia that’s commonly found on the scalp. It can usually be managed effectively with over-the-counter remedies and often resolves on its own after middle age.
Despite these key differences, the two scalp conditions can look and feel similar at times. “Even for a dermatologist, it can occasionally be difficult to tell the difference between scalp psoriasis and dandruff, also known as seborrheic dermatitis,” says Shira Wieder, MD, a board-certified dermatologist at Montefiore Einstein Advanced Care in New York City. “In fact, there is even an overlap category we call sebopsoriasis.” That said, there are a few distinguishing characteristics that you can look for.
First, assess whether dryness and flaking are widespread across the scalp or confined to specific areas. “Generally, with dandruff, the borders of the flaking areas are poorly defined and the flakes diffusely scattered, while in psoriasis the plaques are well demarcated,” Dr. Wieder says. Another factor to note is the color and texture of the flakes themselves; dandruff tends to be yellowish-white, fine, and greasy, while psoriasis produces flakes that are silvery-white, thick, and dry.
If parts of your scalp look highly inflamed, that’s another sign that you may be dealing with psoriasis. Psoriasis plaques usually appear red or pink against lighter skin or brown, purple, or gray against darker skin. On the other hand, with dandruff, color changes of the skin are less common, Dr. Wieder notes. Temporary hair loss can also be a sign of psoriasis.
Another consideration is whether you’ve experienced similar skin symptoms beyond your scalp, since both psoriasis and seborrheic dermatitis may crop up in multiple locations. “We can often look to other areas of the body to help make the diagnosis,” Dr. Wieder says. “Seborrheic dermatitis can often also be found in sebaceous gland–rich areas, including the hairline, sides of the nose, within and above the eyebrows, and behind the ears. Psoriasis plaques, [on the other hand], are often found on the elbows, knees, the cleft of the buttocks, and nails.”
Finally, if dandruff shampoos have not done much to ease the itching and flaking, that could be a clue that you actually have psoriasis—with an important caveat. “I find that people often don’t use dandruff shampoos correctly,” Dr. Wieder says. “They need to be left on the scalp at least five minutes to have an effect before rinsing off. So when I’m assessing a patient who [thinks they have] dandruff that’s not responding to the over-the-counter topicals, the first question I ask is how they use them.” She also suggests trying a couple of different active ingredients. For example, some shampoos contain selenium sulfide or pyrithione zinc to treat yeast overgrowth, while others contain ketoconazole. “If dandruff shampoo has never helped despite being used properly—or has helped only minimally—that’s a good time to see a dermatologist to make sure there isn’t something else going on, like scalp psoriasis,” she says.
