Psoriasis is a skin condition that often runs in families. It is caused by an abnormally accelerated replacement of skin cells. Skin cells in healthy individuals are replaced every 3-4 weeks but this is increased to 2-6 days in psoriasis sufferers. This leads to the formation of psoriatic plaques which are raised red patches of skin that are covered with silvery white scales. Psoriasis is often itchy and can also feel sore.