Autoimmune disease. A breakdown of the body's immune system, which defends you against infections. The immune system mistakenly attacks your own cells. This can cause an autoimmune disease like psoriasis.
Erythrodermic psoriasis. A serious type that affects most of the body. Symptoms include red skin, lots of shedding, itching, pain, and body temperature that goes up and down. An outbreak usually requires you go to the hospital. It is the least common type.
Guttate psoriasis. The second most common type, mostly found on children and young adults. The spots are much smaller and not as thick as those of plaque psoriasis. They usually show up on the trunk, arms, and legs. They often happen suddenly with a cold or other respiratory infection, or after tonsillitis or strep throat.
Immune system. Your body's natural defense system, which helps fight infections. When the immune system mistakenly attacks your body's own cells, it is called an autoimmune response -- which can trigger an autoimmune disease like psoriasis.
Phototherapy. A treatment that involves brief exposures to ultraviolet light -- ultraviolet B (UVB) or A (UVA).
Plaque. Patches of scaling skin that cover sores. They usually appear on elbows, knees, and trunk.
Plaque psoriasis. The most common type. Eighty percent of people with psoriasis have this kind. It appears as raised, inflamed, red patches with silvery, white, or red scaly skin. Most often on the elbows, knees, lower back, and scalp.
Psoralen and UVA light therapy (PUVA). A treatment that involves taking medication called psoralen, which makes your skin more sensitive to light, before a brief exposure to ultraviolet A (UVA) rays.
Psoriatic arthritis. A type of arthritis that may happen in someone with psoriasis. The fingers and toes are most often affected. People with pustular psoriasis or psoriasis of the nails are more likely to develop this type. Ten percent to 30% of people with psoriasis get it.
Pustular psoriasis. A type with non-infectious, pus-filled pimples in red skin. It can be very painful, and you may need to go to the hospital.