Dandruff is the shedding of excessive amounts of flakes of dead skin from the scalp. It is a cosmetic problem experienced by hundreds of millions of people in the world but it is not contagious. It is often accompanied by itchiness of the scalp. Dandruff is sometimes confused with dry scalp but it differs from it in that it is improved when one shampoos more often.
Skin cells are constantly renewing themselves. When skin cells on the scalp are renewed, the old ones are pushed to the surface, leaving the scalp. In a normal healthy scalp environment this renewal process is unnoticeable. With dandruff, the skin renewal speeds up, so that a bigger amount of dead cells are shed in clumps, which are big enough to be seen with the naked eye as embarrassing white flakes.
There are several types of dandruff and each of them is a result of a different medical condition. Common dandruff is believed to be related to a fungus known as malassezia, which normally lives in the human scalp. In some cases, the sudden proliferation of this fungus results in the flakiness of the skin characteristic of dandruff. The reasons for this overgrowth of fungus are unclear. Dandruff sometimes develops as an allergic reaction to chemicals contained in hair care products, such as solvents used in Rogaine and other minoxidil-based lotions.
Seborrhoeic dermatitis of the scalp is another form of dandruff. With seborrheic dermatitis, the scalp becomes red and inflamed and the skin flakes off. This type of dandruff is more severe than common dandruff and it is characteristic of greasy, bran-like scale. The seborrhoeic area may be red and itchy and it can affect the eyebrows, ears, scalp, the skin around the nose, the lines on the cheeks, forehead and armpits. This condition becomes worse in winter and tends to improve in summer when sunlight relieves its symptoms. Cradle cap is a relatively harmless form of seborrheic dermatitis occurring only in infants and it usually goes away before the baby turns one year old.
Psoriasis is an unpredictable type of skin disease often affecting the scalp. In psoriasis, the skin becomes itchy and skin cells grow quicker than normal, causing the scalp to thicken and flake. Besides the scalp, the resulting silvery scales also occur on the knees, lower back and in areas of the body where there are folds of skin. Psoriasis is not contagious. Although the cause of psoriasis is unclear, it is often believed to be an autoimmune disease. Its manifestation is the same as with common dandruff or seborrheic dermatitis, which is the rapid shedding of skin.
Although it is not exactly known what causes the aforementioned dandruff-triggering conditions, it has been observed that excessively oily scalp, hormonal imbalances, autoimmune disorders, elevated scalp sensitivity, extreme stress, Parkinson disease and heart diseases lead to an increased occurrence of dandruff.