Question
Hello,
I'd like to say thank you for your show. I enjoy it thoroughly.
I have a question most of my friends laugh at.
I heard a while back that you are more likely to get sunburn if you are wearing sunglasses. I have put the theory to the test and it has worked for me. I didn't put on sunscreen or wear sunglasses, sun bathed for a few hours and I did not get sun burn. Then I did not put on sunscreen and wore my sunglasses, had sun burn within a couple hours. Of course I don't abuse this theory, I know eventually everyone will burn, especially fair skin . ( I am not fair skinned. )
I found some information on the internet: this link (quoted below) and then this one (more in depth).
*DO SUNGLASSES CAUSE SUNBURN?*
SKIN colour changes when you are exposed to the sun because your body is told to produce more melanin - skin pigment - by your pituitary gland.
Melanin stops your skin from absorbing ultraviolet light.
It is this ultraviolet light which has the effect of burning the skin.
But the pituitary gland only knows how much melanin to make from the signals it gets from the eye. If the eye says it's sunny, the pituitary gland goes into overdrive.
But with shades on, the gland is fooled so less melanin is produced - meaning a higher risk of burning.
With your access to some of the top brains in science, could prove or debunk this theory? I know you probably have hundreds upon hundreds of questions coming to you weekly, so if you can't get to this question anytime soon I understand, but if you are able to address this, I would be grateful. Thanks again for your great podcasts. I have listened to other podcasts, but I have to say your ability to get "down to the brass tacks" makes your show a lot more enjoyable and informative.
Cheers,
-Michael Patella
Winston-Salem, NC USA
Answer
We posed this question to Cambridge Laboratory of Molecular Biology scientist Mick Hastings, who shed some light on the subject...
Mick - The bottom line is, no, but it is an intriguing question. Melanin is produced in response to light actually in the skin itself. It doesn't come from any glands, but there is a gland called the pineal gland - not the pituitary gland, the pineal gland - which produces something called melatonin.
The interesting biology here is that melatonin can affect pigmentation of the skin in amphibians. In fact, that's how it was discovered. But melatonin has no effect on the skin of humans.
It's actually melanin that makes us go darker in response to the sun. There's still another neat piece of biology underlying this, and that is to say that, in recent years, what's been discovered is a completely novel set of light responsive cells in the retina called intrinsically photoreceptive retinal ganglion cells. They're nothing to do with enabling us to see the world around us, but they are there for us to sense changes in light intensity and quality. These cells have a very important affect on our mood, on our biological clocks and our circadian rhythms.
So, at some level, if one were to wear sunglasses, it would affect not just how we see the world in terms of objects, movement and colour; it would also affect our response in terms of our mood, which would include heart rate, pupil contraction, things like this.
So there are some subliminal effects of light on the body which will be influenced by wearing sunglasses but to cut to the chase, this will not affect whether or not we're more or less sensitive to sunburn and sun tanning!
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Comments
Sure. But...
MSH (melanocyte stimulating hormone) is indeed produced by the pituitary; it's cleaved from a larger precursor molecule called POMC (proopiomelanocortin). Stimuli that place a high burden on the pituitary, such as pregnancy, also tend to result in increased skin pigmentation because the MSH that is cleaved out of the precursor is active around the body. This is why pregnancy is temporarily associated with darker skin tones.
But the question is about sunglasses and sunburn, and it speculates that the stimulus for sun tanning could involve light detection by the eye which, in turn, results in a reflex increase in skin melanisation to provide protection. Here we argue that this is not a significant mechanism. The best evidence for this is to look at the face of someone who has been skiing - and wearing goggles - recently. They will have classic "panda eyes" where the bits of skin behind the goggles, which have been protected from UV exposure, are untanned.
I suppose one could argue in this context that sunglasses might lead to sunburn, because that paler skin is subsequently much more susceptible to skin damage than the surrounding tissue, but I don't think that's what the questionner had in mind!
Actually...
The pituitary gland (which is a real thing) does affect melanin production, through the melanocyte stimulating hormone.
Im unsure if the pituitary gland is stimulated by skin receptors or eye receptors (or both) re: the presence of UVR. As this page is the first that pops up on Google when I search for this, it would be great if you could update your content here to provide people with accurate information.
Thanks!
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