Risk factors for psoriasis include:

• Age under 20. About 40% of people develop the condition before age 20. Psoriasis (most often plaque psoriasis) can even occur in infants.
• Climate. Some studies have found that the disorder develops earlier and more frequently in colder climates. For example, psoriasis occurs more often in African-Americans and in Caucasians who live in colder climates than in people of any ethnicity who live in Africa.
• Ethnicity. Psoriasis is uncommon in Native Americans of either North or South American descent.
• Family history of the disease. About 35% of those with psoriasis have one or more family members with the disorder.
• Male gender. Some studies have indicated that more men than women have psoriasis.