Eczema and psoriasis both cause red, scaly rashes that come and go. However, eczema favors the crook of elbows and knees, and psoriasis is on the outside of joints. Eczema can make skin look dark and leathery, while psoriasis features silvery scales. Both are immune system-related, but eczema involves the overproduction of T-cells and psoriasis is an autoimmune disease that targets skin cells.