Casey Gallagher, MD, is board-certified in dermatology and works as a practicing dermatologist and clinical professor.
Psoriasis is an autoimmune disorder that causes lesions or inflamed scaly patches on your skin. It can show up anywhere on your body, depending on the type(s) of psoriasis you have. Psoriasis is believed to be caused by abnormal immune system activity that’s directed at the cells making up your skin and nails. It’s not curable, but it can be managed.
It comes in many types, but plaque psoriasis is by far the most common, making up between 85% and 90% of cases. Some people may have more than one type.
Many rashes are contagious, but psoriasis is not.
This disease can run in families, which can lead to confusion about transmission. However, researchers believe this is due to a genetic glitch in the immune system and not anything you can “catch.”
The look varies by type:
Yes, psoriasis is an autoimmune disease. Experts still don’t know why, but the immune system mistakenly attacks healthy skin or nail tissues like it would a real threat, such as a virus.
Researchers believe a genetic predisposition combines with other factors—such as obesity, stress, or certain medical conditions—to trigger the disorder.
Plaque psoriasis is by far the most common type of psoriasis. It’s characterized by well-defined patches of discolored skin that are itchy, scaly, and flaky. These are called plaques, and they’re caused by skin cells reproducing too quickly, so that they build up on the outermost layer of skin.
Most types of psoriasis are extremely itchy, especially erythrodermic, guttate, and plaque psoriasis. This is due to dry, flaking, and sometimes peeling or cracking skin.
These and other types of psoriasis may also include pain, which can be severe in some cases.
Explore an interactive model showing how a psoriasis rash affects the outermost layer of the skin. This layer is typically comprised of a barrier of dead skin cells that continuously shed and are replaced by new cells. In psoriasis, however, the dead skin cells build upon each other, forming a thick, tough layer of cells that eventually flake off.
An autoimmune disease is a condition in which the immune system incorrectly identifies a type of healthy tissue as a dangerous pathogen, such as a virus, bacterium, or fungi. It then attacks and tries to destroy that type of tissue. More than 100 autoimmune diseases have been identified and they impact more than 23.5 million Americans.
A biopsy is a medical test in which a doctor removes a sample of your tissue to examine it under a microscope. This can be an important step in diagnosing a disease. Many different tissues can be biopsied, including the skin, organs, and bones.
PASI stands for Psoriasis Area and Severity Index. This classification system is used to rate the extent and/or severity of psoriasis symptoms on your skin so doctors can track your progress over time. It rates redness, thickness, scaling, and percentage of skin involved.
The plaques of plaque psoriasis are distinct raised patches of inflamed and discolored skin that are covered with silvery scales made up of excess skin cells being sloughed off. These itchy areas tend to appear during flares of the disease and clear up during remissions.
Topical corticosteroids are steroidal drugs that you use on your skin, especially for inflammatory skin diseases like psoriasis. These drugs are able to penetrate your skin and work directly on the damaged cells. They lower inflammation, slow cell overproduction, alleviate itching, help you shed scaly skin, and improve the skin’s appearance.
U.S. Centers for Disease Control and Prevention. What is Psoriasis? Updated August 18, 2020.
National Psoriasis Foundation. About psoriasis. Updated October 1, 2020.
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National Psoriasis Foundation. Life with psoriasis. Updated October 2, 2020.