Is sunshine a safe treatment for psoriasis?

Summer is just around the corner and we can feel the nice weather calling to us. Sunshine is great for beaches and barbeques, and some patients will say that their psoriasis goes away in the summer, but can sunlight ever be safely used as a treatment for psoriasis?


Heliotherapy, using natural sunlight to treat psoriasis, has a long history and is the grandfather of modern day phototherapy. Unfortunately, solar radiation is not a good substitute for phototherapy in the treatment of psoriasis, and in fact can actually be harmful.

By looking at the places where heliotherapy worked well, notably in the Dead Sea area, scientists started developing UVB light sources to maximize effectiveness and minimize undesired energy. Originally they started with mercury arc lamps, and eventually with Broadband UVB lamps.

This process of getting closer to an ideal light source for phototherapy was helped immensely by the efforts of doctors Parrish and Jaenicke who measured the responses of psoriasis lesions and unaffected skin to different isolated wavelengths of light. In their results, they reported that wavelengths below 300nm were erythemic (burning) without therapeutic effect. Meanwhile wavelengths above 320nm were also not therapeutically effective.

From this, the Narrowband UVB phototherapy lamp was developed by Philips Lighting to be as close of a match to the action spectrum of psoriasis as possible. This puts Narrowband UVB light between the extremely erythemic area below 300nm and the longer wavelengths of light associated with tanning.

Surprisingly, sunlight only has about 2% of its energy in the spectrum needed for treating psoriasis, and much more energy in areas known to be linked to carcinogenesis, premature aging and the like. So, while it is fair to say that some people see improvements to their psoriasis with sunlight, those people would likely also see even better results from Narrowband UVB treatment.
The associated risks of solar radiation from sunlight lead us to recommend caution this summer. We at Daavlin are huge fans of sunscreen for outdoor activities, and would recommend that it is applied liberally before your Memorial Day activities.