No one knows precisely what causes dandruff, though a fungus called malassezia may play a role. It's normal to have malassezia on your skin. Too much of it, though, is linked to dandruff.
These are some of the common reasons that your scalp can get dry and itchy:
Seborrheic dermatitis (or seborrhea): This common skin condition causes redness, itching, and flaking. It can occur on many parts of the body. When it affects the scalp, it's called dandruff. It's treatable. Most often, over-the-counter medicated shampoos will stop the flakes from falling. More stubborn cases will likely benefit from prescription-strength shampoos and steroid creams.
Scalp psoriasis can cause dandruff-like itching and flaking. Psoriasis happens when the immune system triggers too many skin cells to grow on various parts of the body. That can include your scalp. People with psoriasis may be more likely to get dandruff, but psoriasis is not dandruff.
Eczema. This skin condition can make your scalp itchy and flaky. It's most common in babies and children, though anyone can get it. The cause is unknown. Moisturizers and prescription steroid creams can help relieve the symptoms, as can avoiding harsh soaps and scratching. It also helps to avoid stress whenever possible.
Certain diseases, such as Parkinson's disease and HIV, have also been linked to dandruff. People with these diseases have higher rates of dandruff, says Heather Onoday, RN, a nurse practitioner who specializes in dermatology at Oregon Health and Science University in Portland, Ore. Having dandruff doesn't make either of those diseases more likely, however.
A poor diet also has been suggested as a culprit, though Green says there's no proven link. Jeffrey Benabio, MD, agrees.
"We may see associations but we can't say that, for example, vitamin D deficiency from lack of sunlight in winter causes dandruff," says Benabio, a dermatologist with Kaiser Permanente in San Diego. Eating a well-rounded diet is a good idea for your overall health, but having a dry scalp, which Benabio says is uncommon, doesn't mean you're lacking any particular nutrient.
3 Things That Can Make Dandruff Worse
These things don't cause dandruff, but they worsen it if you already have it:
Not washing your hair often enough. "That's the simplest reason," Green says. "It should be washed every day or every other day."
Stress. "Stress makes everything worse," Green says. Stress happens, so what really matters is how you respond to it.
The season. "It's always worse during the winter, when it's really cold out and overheated indoors," Green says.
No matter what's causing your scalp to itch and flake, you can take control. "Over-the-counter treatments work well, but see your physician if they don't work for you," Benabio says.