> Sunburn is triggered when your DNA is damaged from light absorption [...] This interferes with protein synthesis and wreaks havoc in your body over time
Not a skin-scientist, but this seems misleading: Sunburn is not caused by bad DNA floating around or damaged cells pumping out flawed proteins to annoy their neighbors.
Rather, your skin-cells have techniques to measure their exposure, and when they detect that DNA damage might have occurred, well-behaved ones trigger a variety of self-destruct, to mitigate the risk of turning into cancer. The sunburn you see and feel is from cells dying or signalling "I'm compromised, come eat me" to your immune-system.
The details of UV damage are interesting. You can think of DNA as a sequence of four letters: C, G, A, and T. If there are two neighboring T's, UV can move a bond, linking the two T's together (i.e. thymine dimerization). If you're in the sun, each skin cell gets 50-100 of these pairs created per second (which is much higher than I expected). Enzymes fix most of these errors, but sometimes the errors will cause problems during DNA replication and you can end up with mutations.
Does anyone know how UV indexes reported by weather apps (including forecasts) work?
I've found that some sources report lower UV index on cloudy days, whereas some seem to indicate the same index as a sunny day.
It's not clear if these sources all have a different model for UV, some being more sophisticated or conservative, and whether any of them are backed up by a UV meter.
It is a prediction of UV intensity based on specific forecast location, time of day, day of year, prevailing weather, and any anomalies affecting the ozone layer. It is calculated by NOAA.
> the sun may still feel pretty intense in the morning or late afternoon, but the risk of sunburn is considerably lower
This is very misleading. By some coincidence I was just looking into this earlier today.
The lower the UV index, the smaller the window is between the amount of time needed to get enough Vitamin D and the time to get burnt (erythema). So the best thing to do is get sunlight mid-day for a shorter amount of time.
As the UVI becomes smaller, it becomes more difficult to produce sufficient vitamin D without inducing erythema. For low sun conditions typical of midday in the mid-latitude winter (SZA ∼65°), where R∼1, the skin area exposed must be more than 12% (see Eq. 5) This means that for these low sun conditions it is improbable that sufficient vitamin D can be produced from exposing the hands and face alone, since that area is less than 12% of the full body.
Figure 6 shows that for full body exposures, there is a wide window between the time for sufficient UV and the time for too much UV. As the fraction of body that is exposed decreases, the window of optimum UV exposure times also decreases. If only hands and face are exposed, there is generally only a small window between receiving insufficient UV for vitamin D production, and too much UV for skin damage (erythema).
You would do well to calculate the numbers for your own city, as I did earlier today for mine:
I really appreciate learning this fact, but I can't tell how it makes the quoted sentence misleading. The author is just talking about the surprising disparity between how warm it feels and how fast you will burn. They don't mention vitamin D.
I know they don’t mention vitamin D, but I think it’s important for people to know the context and not think that late day sunlight automatically = better
it really only takes about 5 minutes of exposure to get the vitamin D your body needs. i would happily do it between 7-9AM when the UV is low than doing it at mid day.
Toasting my DNA is quite a way to put it. It's an informative read, it helps me understand why the noonday sun does feel so intense. Even if it's not hot, the ability to find shade at noon is so poor, it feels inescapable.
I am curious if anyone else can tell whether it is a high UV day just by looking outside.
There is a certain look to the sky (slightly whiter-bluer) looking against the clouds, and I am not sure if it is because I am directly seeing UV, whether there is some fluorescence, or whether it’s placebo effect.
UV index weighs UVB more heavily than UVA. UVB falls much faster than visible sunlight as the sun gets lower because photons travel through increasingly more ozone and atmosphere. So the higher in the sky the sun is, minus cloud clover, the higher the UV index is.
> Sunburn is triggered when your DNA is damaged from light absorption [...] This interferes with protein synthesis and wreaks havoc in your body over time
Not a skin-scientist, but this seems misleading: Sunburn is not caused by bad DNA floating around or damaged cells pumping out flawed proteins to annoy their neighbors.
Rather, your skin-cells have techniques to measure their exposure, and when they detect that DNA damage might have occurred, well-behaved ones trigger a variety of self-destruct, to mitigate the risk of turning into cancer. The sunburn you see and feel is from cells dying or signalling "I'm compromised, come eat me" to your immune-system.
This whole article shouldn't even exist, and should just point to wikipedia or mayo clinic.
The details of UV damage are interesting. You can think of DNA as a sequence of four letters: C, G, A, and T. If there are two neighboring T's, UV can move a bond, linking the two T's together (i.e. thymine dimerization). If you're in the sun, each skin cell gets 50-100 of these pairs created per second (which is much higher than I expected). Enzymes fix most of these errors, but sometimes the errors will cause problems during DNA replication and you can end up with mutations.
Details: https://pdb101.rcsb.org/motm/91
Does anyone know how UV indexes reported by weather apps (including forecasts) work?
I've found that some sources report lower UV index on cloudy days, whereas some seem to indicate the same index as a sunny day.
It's not clear if these sources all have a different model for UV, some being more sophisticated or conservative, and whether any of them are backed up by a UV meter.
It is a prediction of UV intensity based on specific forecast location, time of day, day of year, prevailing weather, and any anomalies affecting the ozone layer. It is calculated by NOAA.
https://www.cpc.ncep.noaa.gov/products/stratosphere/uv_index...
> the sun may still feel pretty intense in the morning or late afternoon, but the risk of sunburn is considerably lower
This is very misleading. By some coincidence I was just looking into this earlier today.
The lower the UV index, the smaller the window is between the amount of time needed to get enough Vitamin D and the time to get burnt (erythema). So the best thing to do is get sunlight mid-day for a shorter amount of time.
UV Radiation: Balancing Risks and Benefits https://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.2008...
You would do well to calculate the numbers for your own city, as I did earlier today for mine:https://chatgpt.com/share/6ab2f272-a32c-83ea-9fec-49031e4da3...
I really appreciate learning this fact, but I can't tell how it makes the quoted sentence misleading. The author is just talking about the surprising disparity between how warm it feels and how fast you will burn. They don't mention vitamin D.
I know they don’t mention vitamin D, but I think it’s important for people to know the context and not think that late day sunlight automatically = better
it really only takes about 5 minutes of exposure to get the vitamin D your body needs. i would happily do it between 7-9AM when the UV is low than doing it at mid day.
Isn't think only true if getting enough vitamin D is as important to you as cancer?
Toasting my DNA is quite a way to put it. It's an informative read, it helps me understand why the noonday sun does feel so intense. Even if it's not hot, the ability to find shade at noon is so poor, it feels inescapable.
I think I got the worst sunburns when I didn't feel hot at all.
Usually, it involves water, water cools you down, so you don't feel the heat, but it doesn't block UV, so you don't get the warning.
I am curious if anyone else can tell whether it is a high UV day just by looking outside.
There is a certain look to the sky (slightly whiter-bluer) looking against the clouds, and I am not sure if it is because I am directly seeing UV, whether there is some fluorescence, or whether it’s placebo effect.
I don't think so. If you controlled for temperature and season I bet you wouldn't be able to tell.
UV index weighs UVB more heavily than UVA. UVB falls much faster than visible sunlight as the sun gets lower because photons travel through increasingly more ozone and atmosphere. So the higher in the sky the sun is, minus cloud clover, the higher the UV index is.