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 chronic (long-lasting) skin disease of scaling and inflammation that affects greater than 3 percent of the U.S. population, or more than 5 million adults. Although the disease occurs in all age groups, it primarily affects adults. It appears about equally in males and females.