It's instructive to look at people who drive for a living. One arm will have significantly more sun exposure than the other and it's trivial to spot the difference as the sun does have a very noticeable aging effect.

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christophilus 4 days ago | parent | next [-]

I wonder, though, if they got full body sun exposure on a regular basis, if that would change things. It seems unlikely that we would have evolved to have a single part of our body exposed to the sun while the rest wasn’t.

	▲	ndsipa_pomu 3 days ago \| parent [-]
		> I wonder, though, if they got full body sun exposure on a regular basis, if that would change things Yes - their whole body would be subject to the ageing effects of the sun. > It seems unlikely that we would have evolved to have a single part of our body exposed to the sun while the rest wasn’t And yet it's common for dark skinned people to have significantly lighter palms and soles of feet as they have less exposure to the sun.

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cisasteelersfan 4 days ago | parent | prev [-]

What's interesting is that sun exposure through a car window removes almost all UVB rays and most UVA rays. So it's closer to comparing lower sun exposure vs sun exposure with sunscreen.

	▲	apt-apt-apt-apt 4 days ago \| parent \| next [-]
		Dangerously incorrect, side car windows do not remove most UVA rays.
	▲	setopt 4 days ago \| parent \| prev [-]
		If I recall correctly, the side windows on cars let through more UVA, while the front windows block both efficiently.