Summertime is in full swing, and hopefully you are all using good sunscreen. However, recently you may have heard talk that sunblock creams are actually bad for you, increasing the risks of cancer rather than preventing it. Let's investigate the science behind the claims.
A bit of UV science
The sunshine spectrum that reaches the Earth is divided into three ranges: UVA, UVB, and UVC. UVC rays have such short wavelengths that they are all filtered by the ozone layer and do not reach the land surface, so we don’t have to worry about them. UVB rays, with their rather short wavelengths of 290-320 nanometers (or billionths of a meter) constitute only 5% of all ultraviolet radiation that hits the earth and are the ones responsible for sunburns. What’s worse, by damaging skin DNA, UVB causes carcinoma, basal cell cancer, and eye cancer. UVB rays are particularly abundant in summer between 10 am and 4 pm (that’s why they tell you to go to the beach in the morning or late afternoon).
As for UVA, they have longer wavelengths of 320-400 nm and constitute 95% of all UV radiation. UVA rays reach much deeper into the skin, producing tan. You see, UVA light actually damages the skin; in order to protect itself, the skin starts producing dark pigment melanin – thus the brown colour. It’s not just the beautiful bronze tan, however: UVA is the main cause of premature skin ageing and wrinkling. In the past, it was thought that UVA does not lead to skin cancer, but now both the WHO and the US Health department define it as carcirogenous and as the primary cause of melanoma. It has to be noted, though, that exact mechanisms of how UV rays cause cancer are still poorly understood, since it takes many years, even decades, for tanning to lead to a tumour – and decades of study to understand the process, too.
But doesn’t SPF protect me?
- First of all, SPF filter only indicates protection against UVB, not UVA.
- Second, the SPF number doesn’t mean the percentage of UVB that is blocked or filtered – instead, it tells you how much longer it would take you to burn if you didn’t use the sunblock.
For example, if you normally burn in 30 minutes, with a sunscreen that says SPF 30 on it, you will burn in 15 hours – as long as you keep reapplying it! But you will still eventually burn, and UVB will still damage your skin DNA.
The main ingredient in SPF sunblocks is oxybenzone, and studies show that it lowers the risk of carcinoma and basal cell cancer by 25% . And while it does present some health concerns, so far its benefits far outweigh the risks.
And what about protection against UVA? The main UVA-blocking ingredients you’ll find in sunscreens are avobenzone and zinc oxide. While zinc oxide is completely safe, it may not be particularly efficient. Avobenzone has been linked to allergies and production of free radicals, but at the moment it is the most efficient UVA filter.
Bottomline? Always use sunscreen, but don’t just look at the SPF number – search for a broad-spectrum sunblock with the SPF of at least 30 and some protection against UVA. And if someone tells you that sunscreen is dangerous, well, skin cancer is much worse, isn’t it?