Or the other way radiation sickness is the deepest worst sunburn you have ever had.

The sunburn you feel isn't a distress signal from cells warning that they can't be trusted, it's tissue death and an inflammatory reaction triggered by a cytokine response.

It usually goes together with bright direct sunlight in the summer, so I think most people don't learn to notice or distinguish it.

But I find that it's on particular overcast days in the summer, when there is no direct sunlight, that you can feel it intensely without the accompanying sunlight/heat. It reminds me to put on sunblock. But it's not all overcast days -- it's strongest when there's a light cloudy "haze". In contrast, when it's thick clouds approaching thunderstorm, you obviously don't feel it at all.

So it's that kind of thing that's hard to judge before you go outside, but as soon as you do, you get a clear "oh, I definitely need to go back in and put in sunblock" or "oh, this is fine, no sunblock needed today".

The best way I can explain it is as kind of an "oppressive" feeling, almost like a kind of pressure on your skin. Like, you can describe heat that way too -- oppressive or like a kind of pressure -- but in this case, you're feeling those things when there is no heat.

And when you are at the beach on a hot sunny day, I find it kind of magical how the sunblock removes the feeling entirely. It's still sunny and bright and hot, but you don't feel the oppressive/pressure feeling together with it.

This is in Australia where the hole in the ozone layer often results in 10x ‘normal’ UV levels, you can get noticeably burned in a few minutes.

UVB light can promote DNA repair pathways:

Enhancement of UVB-induced DNA damage repair after a chronic low-dose UVB pre-stimulation

https://www.sciencedirect.com/science/article/abs/pii/S15687...

UVA can slow down repair of damage from UVB:

Long-wavelength UVA enhances UVB-induced cell death in cultured keratinocytes: DSB formation and suppressed survival pathway

https://pubmed.ncbi.nlm.nih.gov/33978941/

She has her entire family wearing SPF20 24/365, constantly reminding me 'it's the overcast days that actually do the long-term damage'.

I spent a lot of time out in the sun by the Dead Sea and did not burn at all, since the very low altitude seems to have provided me with extra protection, whereas nearby on the shores of the Red Sea, at sea level, I did burn with similar levels of exposure.

1: How high in the sky is the sun? (Many other factors like time of year, time of day, and latitude feed into this) 2: What is the chance for you at a given time of the sun being blocked by clouds, buildings, etc?