Psoriasis [pronounced sorr-eye-iss-iss], also called Pso, is a chronic, or ongoing, disease that can appear anywhere on the body.^[1][2] Psoriasis most commonly affects the skin, but can also affect the nails.^[2] If you also have swollen, stiff or painful joints, you may have a form of inflammatory arthritis called psoriatic arthritis [pronounced sorr-eye-att-ick arth-rye-tiss] that can affect people with psoriasis.^[3][4]

In Pso, the body’s immune system gets ‘confused’ and attacks itself, making new skin cells grow and build up above and just below the surface of the skin.^[2][6][7] This creates thick red or swollen patches of skin covered in silvery scales called ‘plaques’ that you may recognise.^[7][8] These patches can become inflamed, itchy and bleed,^[7][9] affecting either small or large areas of skin,^[8] but it’s important to remember that Pso isn’t contagious.^[5]

How psoriasis works^[5]10