Psoriasis is a long-term, chronic skin disease characterized by red, itchy, or scaly patches on your elbows, knees, scalp, face, chest, lower back, palms, and the soles of the feet. It goes beyond other common skin rashes in that it may also cause swollen or stiff joints, thickened nails, and skin so cracked and dry that it ends up bleeding. Psoriasis is an immune disorder causing severe skin rash flareups that come and go in cycles. Although more serious than other types of rashes, it tends to improve with treatment over time.