The burning red sunburn fades into a ‘healthy’ brown. The pain has subsided and, in the knowledge that your complexion will spark jealousy in your co-workers upon your return, it all seems like it was worth it. But was it?
To follow-up my previous post about how sun cream protects your skin from the Sun’s powerful ultraviolet radiation, I thought I should write one to explain why exactly it is important to use it and the dangerous, cancer-y consequences of prolonged sun exposure. Just to be clear, I am not trying to preach (and, country to popular belief, I don’t work for a sun cream company), I am simply trying to inform you of the fascinating (and potentially deadly) science that takes in your body, in response to UV radiation from the Sun.
So first of all, what is cancer? Cancer is simply your own cells, but they are growing too quickly, forming a tumour. Due to the speed at which they grow, they starve the nearby healthy cells, eventually killing them. Depending on where this happens it can, clearly, be very dangerous.
Most of the cells in your body need to grow and divide all of the time. Damaged or dead cells are continually lost and replaced by new, shiny counterparts, and life goes on. There are two types of genes that control the rate at which cells divide, which can be thought of as the accelerators (the oncogenes – onco basically means cancer) and the brakes (the tumour-suppressor genes). Genes are made of DNA, which is a code of 4 letters, A, T, C and G (see here for a quick review). If any of the letters that make up this code are changed, the gene is said to be mutated, and this can have drastic effects on its function. If an accelerator becomes over-active, and the brakes stop working, the cells begin to divide out of control, and cancer is born.
UV light targets DNA. Specifically it targets the bases T and C, which are known as the pyrimidines. The energy in a beam of UV radiation causes 2 neighbouring Ts and/or Cs to stick together, forming a ‘pyrimidine dimer’. This can no longer fit into the neat, compact double-helix and when the DNA is replicated, these two bases are missed out. The code has therefore changed, it has been mutated. If this mutation occurs within one of the accelerators or breaks, it can change their activity and potentially cause the cells to grow uncontrollably.
Humans have approximately 20000 genes, so the odds of this happening to a specific gene AND the mutation having the required, cancer-causing effect, are clearly very low. The cell is also able to repair most of these mutations, giving us a slightly better chance in the war against ultraviolet. However, the longer the skin is unprotected and exposed to UV light, the more and more likely this becomes.
This said, don’t be afraid of the Sun! You do also need sunlight to remain healthy, and not just in the sense of avoiding being a recluse who lives in the basement, afraid of natural light. This, I do not recommend. Your skin needs to be exposed to some UV light as it is vital for producing vitamin D, which is important for the maintenance of healthy bones. However, the amount of UV radiation required to produce an adequate, bone building supply of vitamin D is much smaller than the amount that causes sunburn.
It is about finding a balance. You need sun exposure for vitamin D production, general happiness and, obviously, that envy-inspiring tan. But, by triggering the formation of pyrimidine dimers, which are subsequently deleted from the DNA sequence, it is able mutate the DNA. When this happens enough times, a tumour-suppressor or oncogene will eventually be affected, leading to uncontrolled growth of the skin cells.
As I said, I am not trying to convince/force you to use sun cream, all I care about is that you know what is happening under your skin, and hopefully find it interesting.