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Comment by harperlee | Hacker News Reader

So in case anyone just panicked thinking “Wait, so do my car and office windows block cancer producing UV or not??”, this is what I found on cancercouncil.com.au (first google result):

- UVA penetrates deeply into the skin (the dermis) causing genetic damage to cells, photo-ageing (wrinkling, blotchiness etc) and immune-suppression.

- UVB penetrates into the epidermis (top layer of the skin) causing damage to the cells. UVB is responsible for sunburn – a significant risk factor for skin cancer, especially melanoma.

Which contrary to what I knew, links melanoma to sunburn, not DNA damage.

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A good example of what UVA does would be the famous trucker with sun damage to one side of his face-

https://www.huffingtonpost.ca/2012/06/06/bill-mcelligott-sun...

Well this has made me reconsider my lack of use of sun screen. Thanks for sharing.

I'm stuck between a rock and a hard place because this article makes a lot of sense.

https://www.outsideonline.com/2380751/sunscreen-sun-exposure...

I think I'm just going to use daily sunscreen on my face only.

Here's an archive for those getting Oath'd

http://archive.is/aVhiM

Or the source: https://www.nejm.org/doi/full/10.1056/NEJMicm1104059

Melanoma is definitely due to DNA damage; somatic mutation is the principal cause of all cancer. In this case the cause is either direct damage or damage by free radical byproducts created by UV. UV causes a kind of mutation in DNA called a pyrimidine dimer, where two adjacent bases mutate at once. By far the most common mutation in melanoma (reponsible for 50% of cases) is a CC to TT mutation at position 600 of the gene BRAF.

The UV damages the DNA. That step is usually required to produce melanoma cancer. The sunburn causes the deeper cells with damaged DNA to multiply in order to replace the damaged cells.

A single quiescent skin cell with precancerous DNA can be cleaned up by the immune system. A precancerous cell that has multiplied itself to cover a patch of sunburn, activating some of the genes for rapid growth, is much harder to clean up.

Well, when you get sunburn i.e. high UVB exposure, you get high UVA exposure, too. My understanding is, that UVA radiation causes cancer.

But I would like to see some clarification on this topic, too.

UVB causes melanoma, that is also a form of cancer. So typical glass would prevent sunburn and melanomas from forming but not the deep genetic and tissue damage that UVA causes. It is not a bad idea to apply SPF moisturizer before going out if you plan to spend anytime with the sun shining on you.

UVA causes DNA damage (and potentially cancer) indirectly via oxidation.

From what I read UVB melanoma is an "easy" type of cancer.

> So in case anyone just panicked thinking “Wait, so do my car and office windows block cancer producing UV or not??”

I just figured automotive glass doesn't block UV (or at least all of it) since window tinting places always advertise UV blocking as a feature of their films. Cynically I know it could be just empty marketing, but it didn't seem like it.

Of course, ordinary light, while still less energetic, penetrates still more deeply into skin, and it, too causes DNA damage. In situ DNA is damaged by light absorbed by less transparent molecules it is near.

Why are you assuming there isn’t DNA damage when sunburned?

Not that there's no damage, but that sunburned skin is top layer skin that is constantly shedding so won't accumulate damage for decades

Only the most burnt skin is shed. The UV light penetrates further layers.

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