I don’t understand your comment. Getting sunburned is obviously a threshold thing, right? If I get 5× more sun than normal on some day, I don’t get a 5× bigger sunburn, instead I go from no sunburn whatsoever to yes sunburn.
The most common idea (zero-threshold hypothesis) is that if you get, let’s say, 10 joules of energy into 1 square centimeter of skin (after it passes through the tan), you get, let’s say, 1% more probability of having cancer (I’m inventing the numbers), and it doesn’t change whether you received it over 1 second or 10 years or whether it caused a burn or not.
Sunburn happens when this damage happens at once, so many cells die, triggering an inflammatory response, but the zero threshold hypothesis says that whether the exposure was over 1 second (thus giving you a sunburn) or over 10 years is irrelevant to cancer rates.
However, the agricultural worker data suggests that they received, let’s say, 1000x sunburns’ worth of UV along many years, even taking into account their tans, but have much lower cancer rates than a person who received 1000 actual sunburns.
So this suggests that maybe the DNA can repair itself over time in a way that fixes many cancer-causing mutations, such that only a big dose in a small amount of time causes cancer. If this were true for all organs, then, for example, much less money would be spent on nuclear shielding, or there would be much less worry about increasing cancer risk when doing a CT scan. But the increased cancer rate from small doses is very hard to experiment with because you need very big populations to get a statistically significant measurement, like let’s say a group of 10M people where half undergo a CT scan randomly.
Edit: In fact, the DNA repairs all the time, otherwise you would suffer from Xeroderma pigmentosum which causes your skin to burn in minutes on sunlight, and increases cancer risk by a factor of 10000. The question might be whether sunburns overload this repair mechanism in a way that triggers irreparable damage/cancer while constant exposure doesn’t.
Edit 2: (found in a Reddit comment): “If a thymidine dimer isn’t repaired before the next time the DNA is replicated, it can cause major issues. The daughter cells can become either non-viable … or they can become unregulated and cancerous …”
I don’t understand your comment. Getting sunburned is obviously a threshold thing, right? If I get 5× more sun than normal on some day, I don’t get a 5× bigger sunburn, instead I go from no sunburn whatsoever to yes sunburn.
A tan being SPF 2–4 sounds reasonable, see §2.3.
The most common idea (zero-threshold hypothesis) is that if you get, let’s say, 10 joules of energy into 1 square centimeter of skin (after it passes through the tan), you get, let’s say, 1% more probability of having cancer (I’m inventing the numbers), and it doesn’t change whether you received it over 1 second or 10 years or whether it caused a burn or not.
Sunburn happens when this damage happens at once, so many cells die, triggering an inflammatory response, but the zero threshold hypothesis says that whether the exposure was over 1 second (thus giving you a sunburn) or over 10 years is irrelevant to cancer rates.
However, the agricultural worker data suggests that they received, let’s say, 1000x sunburns’ worth of UV along many years, even taking into account their tans, but have much lower cancer rates than a person who received 1000 actual sunburns.
So this suggests that maybe the DNA can repair itself over time in a way that fixes many cancer-causing mutations, such that only a big dose in a small amount of time causes cancer. If this were true for all organs, then, for example, much less money would be spent on nuclear shielding, or there would be much less worry about increasing cancer risk when doing a CT scan. But the increased cancer rate from small doses is very hard to experiment with because you need very big populations to get a statistically significant measurement, like let’s say a group of 10M people where half undergo a CT scan randomly.
Edit: In fact, the DNA repairs all the time, otherwise you would suffer from Xeroderma pigmentosum which causes your skin to burn in minutes on sunlight, and increases cancer risk by a factor of 10000. The question might be whether sunburns overload this repair mechanism in a way that triggers irreparable damage/cancer while constant exposure doesn’t.
Edit 2: (found in a Reddit comment): “If a thymidine dimer isn’t repaired before the next time the DNA is replicated, it can cause major issues. The daughter cells can become either non-viable … or they can become unregulated and cancerous …”