"In general, people with psoriasis do better in summer for two main reasons -- No. 1, there's greater humidity, which helps keep the skin moist, and No. 2, there's more sunlight exposure," says Bruce Strober, MD, director of the Psoriasis and Psoriatic Arthritis Center at NYU Medical Center.
According to the National Psoriasis Foundation, psoriasis develops when the regular system of cell turnover goes awry.
Normally, skin cells are shed every 28 to 30 days and immediately replaced by new ones. In psoriasis patients, however, this process is speeded up dramatically, with cell turnover occurring as quickly as every two to three days.
This, say experts, causes a kind of biological "traffic jam," causing old, dry skin cells to literally pile up on one another, forming the characteristic plaques.
When the air is humid, Strober tells WebMD, the skin is better able to retain moisture, which is key to easing those dry plaques. Moreover, he says, since UVA is a recommended treatment for psoriasis, the natural UVA rays of summer sun can be therapeutic.
That said, experts also tell us there are some summer precautions psoriasis patients need to heed. Among them, a reminder not to overdo time in the sun no matter how much you think it can help.
"You do not need excessive sun exposure to effectively treat psoriasis -- 30 minutes per day of natural sunlight is more than adequate -- and overdoing it could cause significant problems, not only increasing your risk of skin cancer, but sometimes making your psoriasis worse," says Strober.
That's because even a slight sun burn, says Strober, can damage the skin. And that not only worsens psoriasis plaques but can also cause new ones to develop.
"Essentially, sunburn can cause normal skin to turn into psoriasis skin because of the direct damage to skin cells," says Ellen Marmur, MD, chief of dermatologic and cosmetic surgery at Mount Sinai Medical Center in New York City.
Experts say a unique aspect of psoriasis known as the Koebner phenomenon also plays a role. In this instance, any break in the skin or damage to skin cells can exacerbate that rapid cell turnover, causing new plaques to develop at the site of the damage. Experts say excessive sun exposure, which can cause sunburn, can do that kind of damage.