Unlike many diseases, dandruff has a range of causes, but the result is nearly always the same: itchy, flaky skin that's visible in your hair and on your shoulders.
Dandruff basically occurs when the scalp sheds skin cells faster than normal -- the fungus Pityrosporum ovale often accelerates this process. The fungus is present on nearly everyone's scalp, but it can irritate some people's skin, causing dandruff [source: WebMD].
The most common cause of dandruff is simple dry skin, especially during cold, dry winter months. When your dandruff is associated with dry skin, the flakes are usually small and less oily than those caused by other conditions [source: Mayo Clinic].
Skin conditions, such as seborrheic dermatitis, psoriasis, eczema and contact dermatitis, can also result in flaking of the scalp's skin. People with seborrheic dermatitis have red, greasy skin covered in flaky scales, and this condition can affect other parts of the body that are rich in oil glands [source: MedlinePlus]. Psoriasis can also affect more than just the scalp -- it can occur on the knees, elbows and trunk of the body, and it presents itself when dead skin cells form thick, silvery scales. Having eczema -- red, itchy patches of skin -- on your scalp can lead to dandruff, but it doesn't always. Sensitivity to hair care products, or contact dermatitis, can also lead to irritation and a flaky scalp [source: Mayo Clinic].
You may be more at risk of developing dandruff depending on your age and hygiene. Keep reading to learn how to prevent dandruff.