What are the triggers for psoriasis?

Scientists believe that at least 10% of the general population inherits one or more of the genes that create a predisposition to psoriasis. However, only 2% to 3% of the population actually develops the disease. Researchers believe that for a person to develop psoriasis, the individual must have a combination of the genes that cause psoriasis and be exposed to specific external factors known as “triggers.” Psoriasis triggers are not universal. What may cause one person’s psoriasis to become active, may not affect another.

For years, researchers have been studying what factors can trigger the onset of psoriasis. In a March 1993 scientific workshop on “Epidemiology of Skin Disease” at the National Institutes of Health, these issues were addressed by Dr. Gerald Krueger. Dr. Krueger is Professor of Medicine, Division of Dermatology, at the University of Utah School of Medicine. Dr. Krueger suggested that three main factors – stress, skin injury and infection – are recognized as triggers for the onset of psoriasis, causing new lesions or inducing flare-ups.


Last month, you lost your temper with your boss. On that same day, you were stuck in a traffic jam after work. That evening, you discovered your son broke a neighbor’s window with a baseball. It’s 30 days later and for some reason your psoriasis is acting up. Is this outbreak stress-related?

According to Dr. Krueger, it is common for 30–50% of patients to report a flare-up following stress. Studies have shown that a stressful event that occurred 30 days prior to the onset of a flare-up can be the cause. Patients who had stress as a precipitating factor and who then learned to effectively cope with stress, healed better with psoriasis therapy than those who didn’t recognize stress as a precipitating factor.

Dr. Krueger went on to state that because there are many ways to manage stress today — including drugs and behavioral approaches — it seems probable that many patients who flare up secondary to stress could be offered these additional therapeutic approaches in conjunction with more traditional therapies.

Skin Injury

Jeannette’s psoriasis seemed to be in remission. She hadn’t had an outbreak in several months. One afternoon, she slipped on the driveway and badly scraped her knee. A few days later she noticed a new patch of psoriasis around the injury site. Did her abrasion cause the psoriasis to appear?

Some studies show that this reaction, called the Koebner Phenomenon, occurs in 30–50% of patients. Up to 90% of patients who have a flare-up or have had the Koebner Phenomenon in the past, also report psoriasis developing in the injured skin site as it heals.


Eleven-year-old Steven recovered from an upper respiratory infection about two weeks ago. Now his psoriasis is starting to flare again. Did his flu induce the onset of his psoriasis?

Infections, especially strep infections, have also been linked to psoriasis. A study of 245 children revealed that 25% had the onset of their disease after an infection. In children already having psoriasis, 50% had a flare-up within two to three weeks of an upper respiratory infection.

Recent evidence has also demonstrated that Acquired Immune Deficiency Syndrome (AIDS) exacerbates existing psoriasis and will induce it in AIDS patients without any previous history.

Other Factors

We know that psoriasis is an inflammatory skin disease triggered by various circumstances. After onset, it tends to wax and wane but seldom goes into spontaneous remission. Much has been learned of the epidemiology of psoriasis, but there are still many unanswered questions.

In addition to the examples Dr. Krueger cited, diet, climate, alcohol, smoking, weight, medications and drug use can be added to the list of factors to research.

Are they related? Do they cause an outbreak? The National Psoriasis Foundation recently funded a $50,000 grant toward the study of infections and their relationship to psoriasis and if (or how) they trigger the onset of a flare-up. Additional long-term study of the causes, distribution, and control of psoriasis is costly but it is desperately needed to better understand a disease that affects over 7.5 million people in the United States alone.