Psoriasis is a skin disease that causes red, itchy scaly patches, most commonly on the knees, elbows, trunk and scalp. Psoriasis is a common, long-term (chronic) disease with no cure. It tends to go through cycles, flaring for a few weeks or months, then subsiding for a while or going into remission.

Psoriasis is caused, at least in part, by the immune system mistakenly attacking healthy skin cells. If you're sick or battling an infection, your immune system will go into overdrive to fight the infection. This might start another psoriasis flare-up. Strep throat is a common trigger.