Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Psoriasis ?
    ### Response:
    Psoriasis is a skin disease that causes itchy or sore patches of thick, red skin with silvery scales. You usually get the patches on your elbows, knees, scalp, back, face, palms and feet, but they can show up on other parts of your body. Some people who have psoriasis also get a form of arthritis called psoriatic arthritis.
    