Dandruff affects about 50 million people in the United States. The good news is that although Dandruff can be bothersome and embarrassing it is harmless. Oily skin is one of the most frequent causes of dandruff and is marked by red, greasy skin covered with flaky white or yellow scales. Dandruff can also be caused by simply not shampooing enough. When you don't shampoo the oils and skin cells from your scalp can build up causing those annoying white flakes. Overused of haircare product like hairspray, gels and powders can also add to dandruff.

For the treatment of dandruff look for shampoos that contain ingredients such as ketoconazole, selenium sulfide, salicylic acid, sulfur, coal tar, or zinc pyrithione. Leave shampoo on for 5 minutes, then rinse well. 

Here are some common over the counter examples: 

• Zinc pyrithione shampoos (such as Selsun Salon, Head & Shoulders). These contain the antibacterial and antifungal agent zinc pyrithione, which can reduce the fungus on your scalp that can cause dandruff and seborrheic dermatitis.
• Tar-based shampoos (such as Neutrogena T/Gel). Coal tar, a byproduct of the coal manufacturing process, helps conditions such as dandruff, seborrheic dermatitis and psoriasis by slowing how quickly skin cells on your scalp die and flake off.
• Shampoos containing salicylic acid (such as Ionil T). These "scalp scrubs" help eliminate scale, but they may leave your scalp dry, leading to more flaking. Using a conditioner after shampooing can help relieve dryness.
• Selenium sulfide shampoos (such as Selsun Blue). These shampoos slow your skin cells from dying and may also reduce malassezia. Because they can discolor blond, gray or chemically colored hair, be sure to use them only as directed, and rinse well after shampooing.
• Ketoconazole shampoos (such as Nizoral). Ketoconazole is a broad-spectrum antifungal agent that may work when other shampoos fail. It's available over-the-counter as well as by prescription.

You may need to try several dandruff shampoos to find one that works best for you. If one stops working, try another. If that doesn't help, call your doctor.