Psoriasis is a skin disease that causes scaly pink patches. Guttate psoriasis is a particular form of the disease that usually affects children and young adults.It can happen on its own, or as a complication of ordinary (chronic plaque) psoriasis.Often, it follows a bacterial throat infection or tonsillitis.soriasis is a skin disease that causes scaly pink patches. Guttate psoriasis is a particular form of the disease that usually affects children and young adults.