The spots on my legs seemed to be like pimples, but they never went away. I also received minor cuts on my upper leg from a cat scratch. After what is now two or three months, the bruising has gone, but the red, scaly patches are continuing to spread. I'm not sure that I have psoriasis, but information I have found on the internet seems to point in that direction. The progression of this skin disorder is quite depressing, and unsightly to say the least.
Psoriasis appears to be an inherited disorder.
Actually, we really don't know what causes it. It can be activated by any infection, stress, etc. It usually improves with sun light, coal tar applications and topical steroids. Severe cases will require methotrexate. Topical vitamin A has also been used.