Psoriasis (so-RY-uh-sis) is a long-lasting skin disease that causes patches of skin to become red, thickened, and covered with silvery-looking flakes.

What Is Psoriasis?

When the American writer John Updike (1932–2009) wrote a book about his own life, titled Self-Consciousness, he spent a whole chapter describing his personal battle with the chronic * skin disease psoriasis. Updike called the chapter “At War with My Skin.” The word psoriasis comes from the Greek verb meaning “to itch.” The disease causes patches of skin to become red, thickened, itchy, and covered with silvery flakes. The disease may also affect the fingernails and toenails or the soft tissues of the genitals and the lining of the mouth. Studies show that between 10 and 30 percent of people with psoriasis also develop joint inflammation (psoriatic arthritis).

What Causes Psoriasis?

Some research suggests that psoriasis may be due to a problem with the immune system * . The immune system includes a type of white blood cell called the T cell. Researchers have speculated that people with psoriasis may have a problem with the immune system that causes it to make too many T cells in the skin.

People with psoriasis often notice that at times their skin gets worse, and then gets better. The bad times, known as flare-ups or flares, may be triggered by such conditions as climate changes, infections, stress, dry skin, and certain medicines. Flare-ups may also occur after the skin has been cut, scratched, rubbed, or sunburned. People whose relatives have psoriasis are more likely to have it. Scientists have studied families with psoriasis to try to find genes linked to the disease. A number of different genes have been linked to psoriasis, but it was unclear, as of 2016, how these genes work together to cause the disease.

The white scaly rash caused by psoriasis often appears on the legs around the knees.

The white scaly rash caused by psoriasis often appears on the legs around the knees.

What Does Psoriasis Look Like?

Psoriasis causes patches of red, thickened skin with silvery flakes, most often on the scalp, elbows, knees, lower back, face, inside of the hands, and bottom of the feet. These patches are sometimes known as plaques (PLAKS). They may itch or burn, and the skin may crack. The disease can also affect the fingernails, toenails, and the moist tissues that line the mouth and genitals. Those who develop psoriatic arthritis (so-ree-AT-ik ar-THRY-tis) experience pain, swelling, and stiffness of the joints (the places where bones meet).

How Is Psoriasis Treated?

A doctor usually identifies psoriasis by looking carefully at the skin, scalp, and nails. If the problem is psoriasis, the doctor can try various treatments that may clear up the skin for a time. There was, however, no permanent cure for psoriasis as of 2016. The choice of treatment depends on a person's age, health, and lifestyle, and the severity of the psoriasis. No single treatment works for everyone, but most people can be helped. The following are some of the treatment choices.

Psoriasis and Diet

Researchers have recently been studying the effect of diet on the development and treatment of psoriasis. In one study, researchers gave participants a diet of 800 to 1,000 calories a day for 8 weeks. The calories were then increased to 1,200 per day for another 8 weeks. The participants in this study lost weight and experienced a decrease in psoriasis symptoms. From this study the researchers speculate that obesity increases the level of inflammation in the body, thus making psoriasis worse. Therefore, they suggest that a weightloss diet might be beneficial.

Living with Psoriasis

Many people with psoriasis find that it helps to keep the skin moist. Lotions, oils, and petroleum jelly (such as Vaseline) are often useful for this purpose. During the winter months, heaters can make the air inside a house quite dry, so it may help to run a humidifier (hu-MID-i-fy-er), a machine that puts moisture back into the air. It is also a good idea for people with psoriasis to avoid getting harsh soaps and chemicals on their skin. In addition, they should protect their skin from injury by taking such steps as not wearing overly tight clothes or shaving with a dull razor.

See also Autoimmune Disorders: Overview • Skin Conditions: Overview


Books and Articles

Smith, Phillip B., and Nathan C. Johnson, editors. Psoriasis: Types, Triggers, and Treatment Strategies. New York: Nova Biomedical, 2013.

Sterry, Wolfram, Robert Sabat, and Sandra Philipp. Psoriasis: Diagnosis and Management. Hoboken, NJ: Wiley-Blackwell, 2014.


American Academy of Dermatology. “Psoriasis.” (accessed March 19, 2016).

MedlinePlus. “Psoriasis.” U.S. National Library of Medicine, National Institutes of Health. (accessed March 19, 2016).

Merck Manual: Consumer Version. “Psoriasis.” (accessed March 19, 2016).

PsoriasisSPEAKS. “What Is Psoriasis?” (accessed March 19, 2016).


American Academy of Dermatology. PO Box 4014, Schaumburg, IL 60168-4014. Toll-free: 866-503-7546. Website: (accessed March 19, 2016).

National Institute of Arthritis and Musculoskeletal and Skin Diseases. 1 AMS Circle, Bethesda, MD 20892-3675. Telephone: 301-495-4484. Website: (accessed March 19, 2016).

National Psoriasis Foundation. 6600 SW 92nd Ave., Suite 300, Portland, OR 97223-7195. Telephone: 503-244-7404. Website: (accessed March 19, 2016).

* chronic (KRAH-nik) means lasting a long time or recurring frequently.

* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that help protect the body against disease-causing germs.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)