Unless you have been hiding out, possibly on the moon, for the last twenty years you know that getting too much sun can cause deadly melanoma cancer, which is why you should always put on sunscreen to protect yourself in the sun, right?
Actually, despite the conventional wisdom on the subject, this is not exactly true.
The fact is that sunscreen is often ineffective in preventing melanoma, and can often indirectly be the cause of cancer. Not only that, but getting the right kind of sun exposure can arguably prevent skin cancer!
Say what? Sunscreen use is linked to skin cancer?
That probably comes as a surprise if you have been told the exact opposite all of your life, and it may lead you to feel a little bit confused.
So let’s separate the facts from the fiction.
Let’s be straight: melanoma can be deadly if it isn’t caught quickly enough. It is the leading kind of skin cancer in the United States.
But using sunscreen is not an effective way to prevent it. In fact, using sunscreen can put you more at risk for developing melanoma cancer. Here’s why.
First, it’s important to understand the difference between the long and short rays that reach us from the sun. Long rays are called UVA rays, and the short ones are called UVB rays.
The short UVB rays have a more immediate surface effect on your skin and can cause sunburn pretty quickly. They also help facilitate the production of skin-cancer preventing vitamin D in the skin. The long UVA rays penetrate more deeply into your skin and can cause melanoma cancer lesions to form.
Most sunscreen works to prevent sunburn, which means that it is formulated to block out UVB rays, the shorter rays. But it doesn’t protect as well, and in many cases it doesn’t protect at all against the longer UVA rays.
So if you put some sunscreen on and go lay outside in order to get a tan, you stay out longer because you have protected yourself against the risk of getting sunburn. However, unfortunately, the longer you stay out in the sun without the protective effects of the UVB rays, the more you increase the risk of getting cancer, due to exposure to UVA rays.
Conversely, people can develop melanoma without going out in the sun at all.
This could be due to exposure to UVA rays through windows in office buildings, which also tend to block vitamin D producing UVB light. (source)
In fact, according to a study published in the Lancet, “Outdoor workers have a decreased risk of melanoma compared with indoor workers.” That same study theorized that “chronic sunlight exposure can have a protective effect.”
So just how does this work? Why is sunscreen use linked to cancer?
The UVB rays that you block when you put on sunscreen are the same ones that help your body create vitamin D, and vitamin D helps to prevent the onset of skin cancer.
The same thing that’s true of sunscreen may also be true of the indirect sunlight that we get through windows (which block UVB rays, but not UVA rays):
“We hypothesize that one factor involves indoor exposures to UVA (321–400nm) passing through windows, which can cause mutations and can break down vitamin D3 formed after outdoor UVB (290–320nm) exposure, and the other factor involves low levels of cutaneous vitamin D3.
After vitamin D3 forms, melanoma cells can convert it to the hormone, 1,25-dihydroxyvitamin D3, or calcitriol, which causes growth inhibition and apoptotic cell death in vitro and in vivo.
… We agree that intense, intermittent outdoor UV overexposures and sunburns initiate CMM [cutaneous malignant melanoma]; we now propose that increased UVA exposures and inadequately maintained cutaneous levels of vitamin D3 promotes CMM.”
In short, the very sun exposure which can cause skin cancer in the wrong set of circumstances (repeat, intense burns particularly in early childhood) can also prevent skin cancer in the right set of circumstances (healthy vitamin D production).
This also explains why melanoma rates are actually higher in latitudes where people get the least exposure to the sun (above 40 degrees), even when they wear sunscreen:
Populations further from the equator tend to have lighter skin. Melanin blocks UVA very effectively, and the pre-tan melanin of someone with olive skin is enough to block most of the UVA that sunscreen lets through. The fair-skinned among us don’t have that luxury, so our melanocytes get bombarded by UVA, leading to melanoma. This may explain the incredible rise in melanoma incidence in the US in the last 35 years, as people have also increased the use of sunscreen.
Put simply, when you use sunscreen you are in essence letting in the “bad” light, and blocking out the “good” light.
In fact, there is evidence that a deficit of vitamin D may be one of the primary factors that can put you more at risk for developing skin cancer. (source)
So, how can you get safe sun exposure?
One of the best ways of getting vitamin D is directly from the sun. It is important to get the right dose of sunlight, and not to overdo it.
If you are light-skinned, the right dose usually means staying in the sun until your skin has a pink tone, but avoiding sunburns.
With time, these multiple, short exposures will increase the melanin in your skin, giving you a tan. The tan, in turn, will naturally block UVA rays while allowing UVB rays to penetrate the skin and induce the production of protective vitamin D.
When my own family “turns pink,” we use this trick to ensure that our skin doesn’t burn and instead turns into a nice tan.
Risk for melanoma cancer also depends, as briefly mentioned, on how far you are from the equator. There seems to be an increase in the effectiveness of sunscreen in reducing the risk of melanoma depending on how close one is to the equator. Sunscreen seems to be more effective for people who are closer to the equator.
But I’d wager that for most people in the United States, sunscreen can put you more at risk for developing skin cancer. That’s because of our overexposure to UVA rays (thanks to windows!) and our underexposure to UVB rays (thanks to our indoor lifestyles).
FOR FURTHER READING:
Should You Use Sunscreen?
(photo credit: depositphotos)