Short answer: Not likely.

The American Academy of Dematology recently declared UV light to be a carcinogen. That means they believe that exposure to UV light can lead to an increased risk for cancer. However, this does not mean you will get cancer if you are exposed to UV light. Like so many things, UV light has the potential to increase your risk for cancer when you get more than your skin is capable of handling; this usually results in sunburns of varying degrees of severity.

The more often you get sunburned, and the worse those sunburns are, the greater your risk for skin cancer becomes. Does that mean if you avoid UV light you will not get cancer? Far from it. In fact, there are all kinds of problems that are caused by not getting enough UV light and there are many other things that are known to elevate your cancer risk. The secret is, as with so many things, moderation. Virtually all medications are toxic, if taken in large enough doses. Determining the proper dosage is always a balance between figuring out how much is too much and how much is not enough. If you properly follow the directions, you will receive the benefits. Phototherapy is no different than any other medication in this regard.

When the body is exposed to UV light (like anytime you’re in sunlight) it causes several things to happen. Right away it allows and is required for the body to properly process Vitamin D, which is directly related to bone strength and general health. The next thing that happens is the skin cells near the surface (the ones being most exposed) get irritated by the light and call for something known as "melanin". Melanin is what gives our skin color. The condition that causes a complete lack of melanin is commonly known as "albinism".

The nucleus of our cells contains DNA. If our DNA gets damaged, it can cause unpredictable effects. Usually such damage just causes the cell to die off and be replaced; in fact, this happens all the time. But every so often, and for reasons that nobody fully understands, such cells can become cancerous. In order to protect the nucleus, melanin is delivered to the exposed skin cells and collects above the cell’s nucleus to shield it from the the UV light – just like sunglasses.

The production of melanin in response to UV exposure is a natural, normal, protective process. Tanning does for our body what the ozone layer does for the planet. It shields us from much of the UV light. When you develop a tan, your skin is responding properly to its environment. However, if you get too much UV too quickly, you end up actually killing skin cells; we experience this as a sunburn. Unlike the tan response, a sunburn is not a protective reaction. Instead, it is simply the body’s response to cellular damage. 

The proper use of UVB phototherapy calls for regular exposure to slightly less UV than what would cause you to burn. If you are properly following the protocol, you will avoid getting burned.

What that all comes down to is that no link has ever been established between the proper use of UVB phototherapy and an increase in the risk for skin cancer, and that’s over nearly a century of therapeutic usage. It does not stress the internal organs the way many internal medications frequenty do. There is no safer form of therapy.

So the problem does not really appear to be with UV light exposure, but with UV light OVER-exposure. That can subsequently lead to a burn, which can leads to cellular damage, which can lead to cancer. The solution, as with so many things in life, is not to avoid all UV light, but simply to avoid getting burned. That can easily be done by following the standard treatment protocol developed by the National Psoriasis Foundation.