Psoriasis is believed to be hereditary. It is believed that at least 10 percent of the general population inherits one or more of the genes that create a predisposition to psoriasis. However, only 2 percent to 3 percent of the population develops the disease. It is believed that both the predisposition to psoriasis plus becoming exposed to specific external factors known as "triggers" causes the disease to appear.
Guttate psoriasis appears in small red spots on the skin. It is the second most common form of psoriasis. The spots often appear on the torso and limbs, but they can also occur on the face and scalp. They are usually not as thick as plaque psoriasis, but they may develop into plaque psoriasis over time.
One of the most inflamed forms of psoriasis, erythrodermic psoriasis looks like fiery, red skin covering large areas of the body that shed in white sheets instead of flakes. This form of psoriasis is usually very itchy and may cause some pain. Triggers for erythrodermic psoriasis include severe sunburn, infection, pneumonia, medications or abrupt withdrawal of systemic psoriasis treatment.
Erythrodermic psoriasis is a severe form of psoriasis that leads to widespread, fiery redness over most of the body. It can cause severe itching and pain. Skin can come off in this type of psoriasis. It is rare, occurring only in 3 percent of psoriasis sufferers. It generally appears on people who have unstable plaque psoriasis.