There is great variety in the severity of psoriasis from person to person. Also, within the same person, the degree of involvement can vary greatly over time. It frequently gets worse or better for no apparent reason. Why it pops up in some locations rather than others is not explained. Some people have it for only a short time, while others have outbreaks frequently or constantly.

In some cases, psoriasis may affect the nails by causing pitting on the surface, separating the nail from the nail bed and thickening or crumbling of the nail plate.

About five percent of people with psoriasis also have arthritis. Some of these people have a form of arthritis unrelated to psoriasis, while others can have arthritis as a part of psoriasis.