Risk Factors

An estimated 6.4 million Americans (about 2.5% of the population) have psoriasis, and it affects between 0.5 - 3% of the world's population.

Gender. Some studies have indicated a higher prevalence in men than in women.

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Age. About 40% of patients report developing psoriasis before age 20 and 10% had the disease before age 10. Psoriasis (most often plaque psoriasis) can even occur in infants, although mild or atypical symptoms in young patients can make it difficult to diagnose properly.

Family History

About 35% of those with psoriasis have one or more family members with the disorder. One study reported that the lifetime risk for psoriasis is 4% in someone with no afflicted family members, 28% with one affected parent, and 68% with both parents affected by psoriasis.

Geography and Ethnicity

Climate plays a role in risk. Some studies have found that the disorder develops earlier and more frequently in colder climates. For example, psoriasis occurs more frequently in African Americans and in Caucasians who live in colder climates than in people of any ethnicity who live in Africa. Psoriasis is also common in Japanese individuals. It is uncommon in Native Americans of either North or South American descent.