While the exact cause of psoriasis is not known, both genetic and environmental factors play a role. In simplistic terms, an overactive immune system results in inflammation and an increase in the number of times that skin cells divide (approximately 10 times faster than normal).

About 10% of the general population inherit at least 1 or more genes that increase the likelihood of psoriasis, but not everybody develops it.

The risk of developing psoriasis is 10% if 1 parent has it and 50% if both parents have it. Up to 33% of people report an affected family member.