Breaking down this word is “photo” meaning light-induced, “carcino-” meaning cancer, and “genesis” meaning origin or development. Essentially this is light-induced cancer development. In considering which organ is most impacted by light by surface area, the skin is the largest most exposed target for light to cause damage. Note that I am saying “light” and not just UV or ultraviolet light as we are developing an understanding of the direct and indirect impact of other wavelengths of light on the skin. Read more...
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What is photocarcinogenesis?
Breaking down this word is “photo” meaning light-induced, “carcino-” meaning cancer, and “genesis” meaning origin or development. Essentially this is light-induced cancer development. In considering which organ is most impacted by light by surface area, the skin is the largest most exposed target for light to cause damage. Note that I am saying “light” and not just UV or ultraviolet light as we are developing an understanding of the direct and indirect impact of other wavelengths of light on the skin.
How does it work?
It appears that many people think of a sunburn through a cooking analogy. Many of my patients seem to think it is the heat from the sun that is warming up their skin until it hits a threshold and then burns - the same way you could burn a meal if you left it on the stove or the oven too long. But is this what’s really happening? The answer is no, not exactly.
The heat from the sun is in the form of infrared wavelengths of light. This is called thermal or heat energy. The wavelengths for heat are above 780 nm. These are not the wavelengths of light blocked by sunscreen, however.
It is not unreasonable to think about the cooking analogy in some ways but it can be very misleading which is why people can experience sunburns on cloudy days as well as while skiing at high altitudes - in spite of not feeling heat.
So what’s really happening?
The specific wavelengths of light that sunscreen products have traditionally targeted to block or scatter to reduce the impact on our skin cells are in the UVB range of light, 290 to 320 nm. The energy from this portion of the light spectrum induces changes in the superficial cells of our skin in the layer called the epidermis.
The impact of the energy from these wavelengths of light can trigger changes in cells that progress through 3 stages referred to as (1) initiation, (2) promotion, and (3) progression. In other words, you take a normal cell, hit it with UV light and this damages the DNA of cells. UVB induces direct damage to the DNA of our cells but also the formation of free radicals with UV exposure creates reactive oxygen species that can also cause damage to the DNA as well as to proteins and cell membranes.
The damage in those cells transmits down to future generations of cells and can be worsened with further exposure to UV as well as with the formation of free radicals and inflammation in the skin. Once that damage is promoted we have a pre-cancerous change in the skin that has a risk of progressing with further damage and inflammation that promotes the proliferation of these damaged cells.
UVB wavelengths are high energy so they induce more damage than UVA however they also only go as deep as the epidermis. UVA penetrates deeper into the dermis- more on this later. We are learning more about the impact of UVA on the development and promotion of skin cancers.
Once UV damages the DNA of a cell, then what?
So you are out in the sun for a long stretch of time and before you know it you are experiencing the signs and symptoms of a sunburn. The impact of excess UVB is obvious by the changes you are seeing in your skin. This does not mean that skin cancer has developed immediately, it only means that there has been damage to the cells of your skin. However, our skin cells have the ability to repair DNA damage. There is a protein that you may have heard about called the p53 protein that plays an important role in DNA repair. DNA repair is good but not perfect and the repair mechanisms rely on the health of supporting proteins like p53. If p53 is mutated, this could allow a cancer to develop faster.
What happens if you keep getting UV exposure?
After your first sunburn or excess UV exposure, some cells are damaged and these cells, if not repaired fully, will continue to divide and send their mutated DNA to future generations of cells. Your immune system recognizes some of these damaged cells and actually mounts an immune response to try to keep the growth in check.
Why does this matter?
We hear so much about physical means of protecting our skin from UV damage, but the reality is that there are multiple steps along this pathway that interventions can be made to supplement your overall skin health routine. Learning about each of these steps can help provide a more personalized and complete photoprotective method that has a better chance of success than just trying to remember to wear sunscreen every day!