According to the National Psoriasis Foundation, researchers have discovered that at least 10% of the population has a gene that makes them more likely to develop psoriasis. But only 2% to 3% of those people actually do develop it. Experts say this means there must be some combination of heredity and environmental triggers that causes the condition.
Though scientists do not know all the triggers that might lead someone to develop psoriasis or have an outbreak, they do know that stress, injuries to the skin, strep infection, and certain medications can play a role. Flexural psoriasis also seems to be more prevalent in people who are overweight.