Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: vvizards on 21/10/2017 03:03:39
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So I know that the average light skinned person will burn in about 30 min at UV index 6 what I don't understand is how that timing works. If I stayed in the sun for 30 minutes at UV 6 would I get burnt the same as if I went in the sun for 15 minutes, went inside for 15 minutes then went back outside for 15 minutes? How does sun damage build up is basically what I'm asking, what sort of breaks do you have to take from being out in the sun to avoid skin damage?
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If you go out into the sun for 15 minutes, then back in the shade for an hour and then back out into the sun for 15 minutes, I think that is essentially the same as being out for 30 minutes. The damage caused by UV radiation is purely additive (until you're too burnt to recognize), and the inflammatory response that the body produces takes several hours to develop, and at least a day to disappear.
I don't know exactly how long is required, but your body will repair the damage and reduce inflammatory responses over the course of two or three days. (Going out in the sun two days in a row improves the chances of getting a bad burn on the second day because of residual damage). After exposure to the sun (or other bright lights), the skin produces pigments for additional protection (tanning), but the increased protection takes a few days to settle in.
There are also long-term problems that add up, largely resulting from cells that were not properly repaired. This can lead to skin cancer.
Rather than taking breaks, it is best to limit exposure. Never use a tanning bed, and if you are in a region/season with intense sunlight don't go out into the sun during the brightest part of the day (10AM-2PMish), and wear clothing, hats and sunglasses that cover your skin when you do go out in the bright sun. Sun lotion or sun block can be used to protect exposed skin, but cannot be treated as a cure-all.
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How do sunburns work?
A small fraction of UV light striking DNA can cause two adjacent bases on the DNA strand to get joined together.
Enzymes in the cell cannot copy this abnormal segment of DNA, and the cell frequently dies as a result (apoptosis).
If, however, the cell's apoptosis mechanism is impaired, the cell may continue to live, and become cancerous.
I understand that a history of UV damage can sometimes be detected in cancers.
See: https://en.wikipedia.org/wiki/Direct_DNA_damage