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Comment by dade_ | Hacker News Reader

Especially sunscreen on overcast days. UVA doesn't cause tanning or sunburn, but it does pass through clouds and damages the skin.

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Speaking of UV-A, I’m not a conspiracy theorist on this, but it reminded me that a common retort I’ve read given to “RF, routers, etc cause cancer” theories is that those are non-ionizing radiation and therefore are safe.

Yet, UV-A is non-ionizing and definitely does cause cancer. Just a random brain connection that was made.

UV-A is generally non-ionizing, but that doesn’t mean it can’t cause electronic transitions that lead to chemical reactions. https://en.wikipedia.org/wiki/Molecular_electronic_transitio...

UV-A can create Thymine diners in your DNA, for example. No ionization required. https://en.m.wikipedia.org/wiki/Pyrimidine_dimer

Why do people feel the need to deny being “conspiracy theorists?” Many conspiracy theories have been proven true: they were spying on all of your phone calls, they did know that cigarettes cause cancer, etc.

Would it be so surprising to find out that consumer RF was giving us cancer but the tech industry was making too much money off it to tell us?

To me “a conspiracy theorist” is a person with a specific mindset: they dedicate their time to learning about and sharing conspiracy theories - usually they believe in several ones - with an unconscious intention not to find real answers, but to prove their beliefs.

Cautiously suggesting that some unproved assumption may be true and needs more research or using scientific methods to validate it does not make a person “conspiracy theorist” or “freak”, though ,unfortunately, they are often labelled as such in our society.

Because one of those successful conspiracies was to brand the natural word “conspiracy” to imply craziness.

UV-A mainly causes cancer by denaturing proteins such as collagen and vitamin A, which indirectly can cause cancer. That's still heavily dependent on the energy of the photon, so real low frequency radiation like that used in telecoms can't use similar mechanisms.

How do you balance wearing sunscreen with getting the necessary vitamin d exposure from the sun?

I put sunscreen on my face and neck let my arms and legs soak up vitamin D.

Everyone is vitamin deficient in one way or another. We all should supplement anyway, so just supplement vitamin D.

Supplementing vitamin D is unlikely to hurt in most cases (if you're taking a useful form like D3 and if you're not acutely deficient in vitamin A and K2), but it both isn't that effective on its own—oral supplementation tends to take a long time to fix deficiency and may work particularly poorly for people with absorption issues—and doesn't provide the full benefits of sun exposure (nitric oxide being a big one, but there are other immune, blood pressure, and inflammation benefits, as well as stuff related to how vitamin D is produced through sun exposure to the skin).

For me, better mental, cardiovascular, immune, and bone health is more important than apparent skin aging and a marginally increased risk of skin cancer, but everybody has to make their own trade-off decisions. A moderate amount of sun exposure is beneficial to most people. Avoid burning—especially severe burns with kids, which seem to be a big factor in eventual skin cancer risk—by controlling length of exposure and by wearing clothes to cover your skin if you can't control length of exposure.

Our skin needs a moderate exposure to the sun, like 3-4 times a week for 15 minutes in summertime.

If it were that simple…

Parameters that affect exposure time to produce a certain amount of vitamin D:

* Date, time

* Location

* Skin type

* Body exposure

* Clouds

* Ozone

* Elevation

* Surface

Here is a calculator from the Norwegian Institute for Air Research:

https://fastrt.nilu.no/VitD_quartMEDandMED_v2.html

https://fastrt.nilu.no/README_VitD_quartMEDandMED_v2.html

In addition, vitamin D requirements and synthesis might vary between people and health status.

Thank you for sharing the calculator. I see there are many external parameters to consider, and variety between people and health status adds to the compexity.

I think it renders the approach to calculate sun expose time unreliable and, probably, useless for most people. Are there other ways? Can I reliably measure my current and required levels of vitamin D, ideally without going to the doctor every week? Or could I just rely on common sense - make sure I spend time outside, but avoid exposing my skin for longer than 30 mins on sunny summer days?

I don’t know of any way that is more reliable or less risky. There are more accessible ways (e.g. maximize time outside without burning), but I wouldn’t think of them as reliable, safe or time-efficient.

Determining vitamin D levels will vary by country. You’d have to research how it works.

I’m not aware that healthy people can get too much vitamin D from the sun. In combination with the many beneficial effects of natural light (see melatonin, circadian rhythm, mood, etc.), maximizing time outside without burning seems like the best strategy to me. I just find it easier to avoid getting sunburn with the above calculator. Day-by-day variations are small enough that you might be able to make educated guesses most of the time and not check every time you go outside.

If this collides with one’s life (e.g. work-hours), supplements could be considered, but those come without the other effects of natural light.

To check the current UV index and ozone column:

https://www.temis.nl/uvradiation/nrt/uvindex.php

+1. Some of the worse burns I had were during overcast days.

I hear this a lot but do not remember a single sunburn on an overcast day despite having very light skin. Is this a southern latitude thing?

Latitude makes a huge difference. The UV index is 13 in Mexico City today vs 5 in London. Depending on your skin type, you would burn in 10 minutes in Mexico City vs 30-45 minutes in London.

This is because sunlight hits the Earth at more of an angle the farther north and south you get, so it passes through the atmosphere for a longer time and more UV gets absorbed before hitting you. This is the same reason you don't burn as much in the early morning and late afternoon.

I was of the mindset that elevation was more of a factor in UV index than latitude, but I just learned differently. Thank you.

I found a nice discussion of the calculation: https://www.epa.gov/sunsafety/calculating-uv-index-0 It hand waves a bit on how latitude is factored in but states clearly that every km of elevation increases exposure by about 6%.

Mexico City: 2,240 m London: 25 m

So 12% more UV for Mexico City based on elevation. The elevation is important but not the primary factor.

Anecdotally, I have been in Mexico City. I did most of my walking in the mornings and still would sunburn on an sixty minute walk. I did not use any protection.

The altitude of Mexico City would also have an effect, compared to a location like Singapore at sea-level.

Time-of-day would have far more bearing than latitude, since most human population is within ±45.

I’ve never had a sunburn from a cloudy day in Australia.

Mexico City is near the equator (1,342.38 mi). London (3,558.31 mi) and Australia (Sydney: 2,339.14 mi) aren't? Though Darwin is closer (860.93 mi) to the equator than Mexico City. So I guess you could be right but if you're like most people and live in NSW or Perth, you probably live a lot further away.

I'm black, and thought I couldn't burn.

Then I visited Panama.

You learn something new everyday, whether you want to or not. :P

Clouds do tend to diminish UV, but not significantly so as to make you UV-invulnerable.

In the UV tracking app I use, the largest cloud-effects I’ve seen are in the range of 1-3 points decrease. So, UV index of 5-7 instead of 8.

Depending on the baseline UV level during exposure, that difference could be significant (5 index down to 2) or not that significant (14 down to 11), in terms of expected minutes until sunburn.

I've had a few living at 49degrees north and it happens in spring with temperatures around 20. You feel comfortable, light cloud cover makes the sun unnoticeable and you're playing tennis for four hours around noon. Right around dinner time you notice that you've got a pretty solid burn that just crept up on you.

As I understand it (and this seems too pat) UV-B "burns" and UV-A does the cancerous damage. I believe it's to do with depth of penetration.

So you can get skin damage without burn.

I got sunburned on an overcast day in Ireland, of all places.

Walking around a whole day outside without anything covering my head turned out to be a bad idea.

agreed. I live in Canada and can't recall ever getting a burn on an overcast day.

The max UV index in Toronto tomorrow is a 6. On a sufficiently overcast day, that may become a 3, maybe even lower. That would have a very significant effect on odds of sunburn.

Equally overcast on a high UV day in Bangkok on the other hand...

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