Psoriasis is a skin condition which causes thick, scaly rashes on the skin. A dysregulated, overactive immune system causes the normal skin replacement process to speed up, resulting in thickened inflamed skin. There are 5 types of psoriasis, classified based on their distinctive appearance. The most common form is plaque psoriasis, where the rash appears as pink, raised patches with some silvery scales. Some types of psoriasis, for example pustular psoriasis and erythrodermic psoriasis are rarer but can be life threatening. Guttate and inverse psoriasis are the other forms of psoriasis. For some patients, the inflammatory process underlying psoriasis can also affect the joints. This condition is called psoriatic arthritis and presents as painful, stiff joints.