As if those white flakes speckled throughout your hair and on the shoulders of your shirt weren’t bad enough, dandruff tends to come back even after you think it’s gone. In fact, dermatologists say dandruff—which is simply defined as white flakes of dead skin in hair, which can be caused by a variety of factors—is one of the most common chronic skin issues they see. And while it isn’t serious, a stubborn case can be embarrassing and bothersome, possibly including an itchy, scaly scalp. There are a few common causes of reoccurring dandruff:

• Dry Skin Whether it’s due to a change in the seasons or your natural skin type, dryness—regardless of where it happens on your body—is no fun. Low humidity has been proven to exacerbate dry scalp and dandruff.
• Sensitivity to Your Hair’s Natural Fungus It’s pretty unappealing to hear, but most of us harbor a yeast-like fungus called malassezia on our scalps. For some, this fungus irritates the scalp and causes more skin cells to grow. When those extra cells die and fall off, they appear white and flaky in your hair and on your clothes.
• A Poor Diet A lack of certain nutrients, particularly zinc, B vitamins and healthy fats—all of which help skin stay nourished and healthy—can increase your chances of having dandruff.
• Irritated, Oily Skin One of the most frequent causes of dandruff is an inflammatory condition known as seborrheic dermatitis—red, greasy skin covered with flaky white or yellow scales on your scalp. It can also appear in other areas that have many sebaceous (oil) glands, like your face, breastbone, back, groin, armpits or behind the ears.
• Your Shampoo Routine While washing your hair every day isn’t necessary unless you have very oily hair, if you don’t lather up your strands and scalp every other day or so, dead skin cells and natural oils from your scalp can build up, causing dandruff.
• Allergies If you’re sensitive or allergic to the ingredients in your shampoo, conditioner, hairspray or other hair products, the result can be a red, itchy, dry scalp known as contact dermatitis—and that irritation can lead to dandruff.

The reassuring news is that dandruff can be treated and ultimately cured; it just may take some time to see long-lasting improvement. If you have a mild case, there’s a good chance that washing your hair with a gentle cleanser will work. (Try switching to a new shampoo to rule out contact dermatitis.) This will help reduce oil and dead skin cells in your scalp. Or, try a dandruff-specific shampoo, which may include a range of ingredients proven to heal dry scalp, including:

• Zinc pyrithione, an antibacterial and antifungal
• Coal tar, a byproduct of the coal manufacturing process, which slows the speed with which skin cells on the scalp die and flake off
• Salicylic acid, which exfoliates the scalp, getting rid of dead cells
• Selenium sulfide, which slows the death of skin cells and may also reduce the malassezia fungus
• Ketoconazole, a broad-spectrum antifungal product
• Tea tree oil, an all-natural antiseptic, antibiotic and antifungal

Keep in mind that you have to scrub these shampoos into your scalp and leave them on for at least five minutes; this gives the ingredients time to work. If you’ve washed your hair with an over-the-counter dandruff shampoo containing one of these ingredients and you still can’t escape the white flakes, ask your doctor or dermatologist if it’s time to prescribe a prescription-strength shampoo or steroid lotion. While you’re talking to your doctor be sure to discuss all your symptoms so he or she can help pinpoint the exact cause of your dandruff.