Psoriasis has perplexed sufferers and their doctors ever since the skin condition was first described. It persists as a major medical problem around the world, with an estimated 7.5 million sufferers in the United States alone.

Question: What is psoriasis?

Answer: There are several types of psoriasis. Most types result in raised patches of skin that are red and become covered with a scaly white covering of dead skin. These patches can be itchy and painful. However, psoriasis can even affect the fingernails and cause arthritic symptoms in some people.

The National Psoriasis Foundation considers this chronic skin condition to be caused by an autoimmune mechanism. In psoriasis it seems that the immune system inappropriately speeds up the growth cycle of skin cells on various parts of the body, and this leads to the common symptoms of the condition.

Q: What do doctors think causes psoriasis?

A: No one seems to have a widely accepted answer to this question, and there is likely more than one cause. What seems clear is that specific immune cells called T cells mistakenly attack healthy skin cells and create an inflamed condition characteristic of infection or wound healing.

What causes the T cells to function this way is not known, but researchers speculate that it might be related to a combination of genetic susceptibility and environmental factors. Also, psoriasis symptoms can clear up and return for no obvious reasons.

Q: Are there common triggers for psoriasis flare-ups?

A: The Mayo Clinic Web site lists some common things that can trigger psoriasis. These include injuries to the skin (scrapes, bug bites or severe sunburn), stress, cold weather, smoking, heavy alcohol consumption, a variety of medications and infections such as strep throat.

The link with strep throat is interesting. Some researchers have proposed that the streptococcus bacteria that commonly lives inside of tonsils is capable of producing “;superantigens”; that, through a complex series of steps involving the immune system, can trigger the symptoms of psoriasis. Although much more research is needed to prove this theory, one study reported that people with psoriasis had strep throat infections 10 times as often as usual. Also, some cases of partial or complete recovery from psoriasis have been reported after tonsil removal. However, there was no way to prove that the psoriasis remission was related to the tonsillectomy.

Q: Do diet and nutrition play a role in the disease?

A: A variety of nutritional factors are being studied. These include the omega-6 and omega-3 fatty acids, wheat gluten, antioxidants and vitamin B-12. None of these have emerged as clear-cut major factors in psoriasis, but they might help some patients. Though not a cure, prescription vitamin D analog skin creams can help reduce symptoms. Oral vitamin D supplements also might help, but combining supplements with the use of creams should only be done with medical supervision.

Since the immune system is clearly involved in psoriasis, maintaining an overall healthful diet that meets all nutrient needs is likely important. Many nutrients are known to be essential for normal immune function, so a wide variety of nutritional deficiencies could be involved and they could be different from one sufferer to another.

Joannie Dobbs, Ph.D., C.N.S., and Alan Titchenal, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dobbs also works with University Health Services.