Dandruff
The most common cause of an itchy scalp is dandruff, the shedding of skin cells from the scalp that results in small "flakes" on the scalp. Dandruff causes mild, but chronic itching. It is usually caused by dry skin, and, for that reason, is most common in winter. It is also determined by genetics, in which case it is likely that a person who has dandruff will most likely have it for the rest of life. Fortunately, dandruff is easily relieved through hydrating shampoos for mild cases or medicated shampoos for more severe cases.
Lice
Head lice are the second most common cause of itchy scalp. They often cause a more severe itching sensation than dandruff, from the lice biting the scalp. They appear on the scalp differently as well, as small white buds on the shaft of the hair. They also cause more itching in localized areas of the scalp, such as behind the ears and at the nape of the neck. Lice, like dandruff, are treated with medicated shampoos. They also require combing out the nits (the lice eggs) with a fine-toothed comb, and washing all bed sheets and pillowcases since lice are extremely communicable.
