I was a bit shocked when a friend of mine said she puts sun screen on every morning as a face cream. It would be a fine thing to do someplace where there is lots of sunshine, or at least lots of UV light, but she lives in Seattle; it’s so far north that there is no way of getting a sunburn during the winter months. There just isn’t enough light.
It got me thinking about how sunscreen has been sold as this necessary thing. We have to block the harmful UV rays. They might cause cancer (which can usually be easily removed) or wrinkles (which we get anyway) or skin damage. Of course, we also know that vitamin D is necessary for human health, and we’re currently learning that it’s not just for kids and growing bodies. It’s necessary for a healthy body - and lack of vitamin D has now been linked to heart disease, cancers, auto-immune diseases and what most of us would call general health. It’s been in the news quite a bit recently, and there’s a selection of the information here.
So how do we get vitamin D? Well, either we eat LOTS of fatty fish (i.e. live like an Inuit), we take vitamin supplements, or we make sure to spend some time in the sun. Not weak sun, not filtered winter sun, not even cloudy day spring sun, but real, honest to goodness bright sunshine.
Now, I do know that UV light causes skin cancer, particularly in pale skinned Europeans who spend time outside in sunny climes. Caucasians living in Australia really should take care. Even in northern climes, I do not mean that you should never use sunscreen. I do mean that everyone needs to figure out their own balance based on where they are, who they are, and their lifestyle. Even if your skin is black as night, you need to wear some sunscreen, sometime -- like on a sailboat near the equator, for instance.
So how do you know when to put on sunscreen? Well, first make sure you’re getting your vitamin D. If there isn’t enough UVB to bring up your vitamin D levels, then there isn’t enough to cause skin damage, either. Some dermatologists will say that any UV is bad because it can cause changes in DNA. UV light does change DNA, and I don’t dispute the molecular effects. I just think that we are highly developed organisms, and our bodies can repair slight damage. As scientists, we don’t yet fully understand our own biology, so, for the moment, I’d rather get my vitamin D the way my ancestors. A daily daily regimen of supplements and sunscreen is a relatively new development. These products don’t have extensive epidemiological studies over decades to back them up. Frankly, given the way that sunscreen ingredients are tested, I would not be surprised if they are eventually shown to be as bad for your skin as a *little* UV. After all, skin cancer doesn’t typically show up until over 40 years of age. No sunscreen has been tested for that long, at least not without changing its formulation!
To figure out how much time in the sun you need to get enough vitamin D, have a look at the calculator at the Norwegian Institute of Air Research. They use 30 ug/L in the blood as a healthy level, but it's been shown that your body will find a healthy equilibrium. Even doubling the exposure time needed for that amount of vitamin D won’t cause a sunburn. You need about 4x the vitamin D exposure to get skin damage. The calculation depends on your skin tone (how easily you burn), how much UVB is coming in from the sun, and how much UVB is reflected from your surroundings. To figure out how much UVB is coming from the sun, it needs to know your latitude, the time of year, and the weather conditions. It assumes that you have 25% of your skin exposed to the sun, which is a bit much for me, since I never go sleeveless.
Since I live in London, time of year, time of day, and weather are the deciding factors in whether or not to wear sunscreen:
At noon on a sunny day in June or July, it takes about 6 minutes of sunshine to get enough vitamin D, but in January and December, there isn’t enough UVB available to make the vitamin at all, even in full sun at noon. There’s also variation during the day: If I get my sun during the school run at 9 am and 3 pm, I cannot make nearly as much vitamin D as if I go out briefly at lunchtime. Even at the height of summer, though, if I'm wearing a long sleeved shirt, it will take 12 minutes to get my vitamin D at noon. If the skies aren't crystal clear, it will take longer. So I think I can sit in the garden with my sandwich for a few minutes without reaching for the sunscreen first. It's probably good for me! On the other hand, if I'm at the beach, at high altitude, or on snow I'll reach for the sunscreen. Reflected light adds up, and I've been burned before under those conditions.
A lot of websites try to provide ‘one-size-fits-all’ advice about sunlight, but it really isn’t appropriate. I’m fair skinned, so I need less sunlight to make vitamin D than someone with darker skin. Moreover, if I add up the periods of sun exposure during a typical school day, it looks like the fair-skinned children would benefit from sunscreen on some days where the darker-skinned children would be getting a barely sufficient amount of vitamin D. Since vitamin D deficiency is well documented, particularly in children with dark skin, and since this group is not at risk of developing skin cancer while living in England, they should not be told to put sunscreen on every morning. Unfortunately, the current dogma is UV=bad, and it will probably stay that way for a while.
