Psoriasis occurs around the world but varies somewhat with geography and race, and with environmental factors like sun exposure.

Climate definitely plays a role in risk; in fact, some studies have found that the disorder develops earlier and more frequently in colder climates. For example, African-Americans and Caucasians who live in colder climates have more frequent occurrences of psoriasis compared to Africans of any ethnicity. Interestingly, Native Americans of either North or South American descent have a very low frequency of developing psoriasis.

In Canada, the highest incidence of psoriasis is in Newfoundland.