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Though it can be a little embarrassing to discover white specks all over your black sweater, there’s no need to hide under a rotation of hats. Flakes happen — but is it just dry skin, the result of unwashed hair, or something else?

Here’s how to tell if your irritated scalp is because of dandruff or psoriasis.

Mainly, the difference is this:

Dandruff

  • Dandruff flakes are usually a reaction to oily or dry skin and, in most cases, are easy to treat with an over-the-counter shampoo.
  • Dandruff can appear all over your scalp without any distinct pattern.

Scalp Psoriasis

  • Psoriasis is an immune disorder that manifests in scale-like flakes on the skin. It can cause chronic discomfort and requires a more intensive form of treatment, since there currently is no cure.
  • A scalp psoriasis rash may be raised and have a noticeable, defined pattern.

Seborrheic dermatitis — er, dandruff

People tend to call any kind of scalp flaking, dandruff, but that’s not completely accurate. In fact, dandruff isn’t even a term typically used in the medical profession, says Jashin Wu, M.D., Founder and CEO of the Dermatology Research and Education Foundation.

“If I had to define it, I would say that it’s mild seborrheic dermatitis.” Though, for the sake of this article and your sanity, we’re gonna keep calling it dandruff.

Dandruff is a condition in which the skin turns red and flakes off. In its mildest form, it affects only the scalp and causes dry white, or greasy yellow, flakes to appear over skin. The area may also burn or itch.

While dandruff most often appears on the scalp, in some cases it can appear in other particularly dry or oily areas, such as the eyebrows, chest, and sides of the nose.

Scalp psoriasis

The skin effects of psoriasis can take several forms, but the majority of cases appear as flakes over reddened skin, covered by silver-gray scales.

Although many sources say psoriasis does not cause itching, there’s evidence that it can, says Antonella Tosti, M.D., a professor of dermatology.

Despite the similarities, a psoriasis rash can be distinguished from dandruff by its distinct pattern — a doctor can confirm this for you.

“Psoriasis is very well-demarcated, so you can see the borders of the rash very easily,” Wu says. “If you do have a rash and it’s kind of ill-defined and not really raised, then that might be dandruff,” he adds.

And while psoriasis can affect skin anywhere on the body, it preferentially causes rashes in certain areas, such as the backs of the forearms, the shins, and scalp.

It’s even possible to develop scalp psoriasis if you’ve never had psoriasis anywhere else on your body.

It’s complicated.

Dandruff

Multiple factors may contribute to the development of dandruff. One popular idea is that a type of fungus called Malassezia, which is normally present on people’s skin, irritates and inflames the skin.

This type of fungus needs oil to grow, so people whose skin produces more oil may be more susceptible to flake-inducing dandruff. There may also be a genetic component.

Other triggers for dandruff include stress, lack of sleep, and low humidity, says Tosti.

Psoriasis

The exact cause is still unknown, but psoriasis is an autoimmune disorder, which means your immune system mistakenly attacks your body’s cells. In psoriasis, skin cells shed more rapidly than normal and flake off.

Genetics play a major role in the development of psoriasis. If a person has psoriasis, the chance that their identical twin would have it’s a whopping 70 percent. Over a third of people with psoriasis have a family history of the disease.

Similar to dandruff, stress and sleep deprivation can cause psoriasis flare-ups. Other linked causes are things like smoking, infection, and obesity, which are linked to inflammation.

“Something that helps us to distinguish [between dandruff and psoriasis] is that dandruff usually improves after shampooing,” Tosti says. That’s not the case for psoriasis.

Typically, dandruff can be treated simply by washing your hair more often with over-the-counter anti-dandruff or coal tar shampoos — though Wu cautions that these treatments don’t cure either condition, and only work in minor cases.

“My suggestion is, if you have scaling of the scalp and you think it’s dandruff, try the shampoo,” says Tosti. If the condition doesn’t improve with daily use of anti-dandruff shampoo, Tosti recommends seeing a doctor.

In that case, it might be severe dandruff that requires a prescription treatment, such as high-concentration antifungal shampoo, or it might be something else — such as scalp psoriasis.

If it’s psoriasis, there are many prescription treatment options available, but the most common is topical corticosteroids.

Even though some of these creams can be purchased over the counter, Tosti notes that the ones available without a prescription generally aren’t strong enough for treating scalp psoriasis.

Other interesting treatments for psoriasis include:

  • Light therapy. Also called phototherapy, where your whole body is exposed to UVB light for controlled periods of time. This is not a tanning bed, which uses UVA light and carries a risk for skin cancer. Light therapy can also be targeted for psoriasis rash hotspots. It’s typically performed in a doctor’s office.
  • Disease-modifying antirheumatic drugs. These bad boys fight inflammation.
  • Biologics. Kind of like the Terminator, if the Terminator was a prescription medication set on blocking inflammatory proteins in the body.

Once the flaking subsides, you’ll probably want to keep in mind ways you can prevent it from happening again.

Dandruff

If dandruff is the cause, frequent shampooing — and possibly lathering more thoroughly when you do — may help.

You may be tempted to return to your old hair care products, but you may need to continue using anti-dandruff shampoo to keep the flakes at bay.

Avoiding triggers such as stress and sleep deprivation, may also be a useful part of your strategy.

Psoriasis flare-ups

Avoiding stress and sleep loss can also help prevent scalp psoriasis recurrences, but unlike with dandruff, shampooing probably won’t be of much use.

Broader changes to your diet and lifestyle can help reduce how often psoriasis flares up. Avoid foods and habits linked with inflammation.

Regardless of whether you have dandruff or scalp psoriasis, keep in mind you might need to make regular treatment part of your routine, so check with your doctor to make a plan that works for you and your symptoms.

If you’re still not sure why your scalp is flaky and Selsun Blue isn’t cutting it, know that dandruff and scalp psoriasis aren’t the only possible causes.

A fungal infection called tinea capitis, for example, may cause scalp flaking, but it’s uncommon in adults who aren’t immunocompromised.

Another possibility is a condition called contact dermatitis in which the skin reacts to something that touches it, such as a hair care product.

“I’ve been seeing a lot of these [psoriasis-esque scalp rashes] after keratin treatments for hair straightening,” Tosti says, explaining that the reaction often looks like severe dandruff or psoriasis.

It’s also worth considering that those flakes may not have resulted from a medical condition at all.

“Sometimes it’s not real dandruff,” Tosti says. “It’s just deposits from hairsprays, from dry shampoos, from a lot of gels, or from other stuff that people put on the scalp.”

Since there are so many possible reasons for scalp flaking, seeing a doctor is always advisable, especially if the flaking is severe or doesn’t clear up after changing hair care products and trying over-the-counter treatments.

In most cases, the conditions responsible for scalp flaking can be treated, so don’t think you need to give up wearing black permanently. Just make an appointment with your friendly neighborhood derm to get those flakes under control.

Nicole Haloupek is a freelance science writer with a canine obsession and a Ph.D. in molecular and cell biology. Follow her on Twitter: @haloupek.