According to WebMD, medicated shampoos are often used in the care and treatment of skin and scalp diseases such as psoriasis. WebMD also reports that medicated shampoos, as well as creams or oils which are used to treat skin conditions, frequently contain salicylic acid or coal tar.
As American Family Physician notes, an excess of dandruff is a common symptom of skin diseases or rashes that occur on the scalp. Medicated shampoos can be very useful in controlling the dandruff and calming the skin disease's other symptoms, such as redness and itchiness. It is recommended to use the medicated shampoo on a daily basis and avoid sun damage.