[miladyincontrol]

Confounding by indication.

People who spend more time outdoors are more likely to try to wear sunscreen, as are people who already got a lot of pre-existing risk to excessive sun exposure.

Key word on try as its greatly assuming there isnt a wide audience who do use sunscreen, then just apply it in poor amount, or never re-apply but enjoy staying out far longer than most do in the sun feeling they're oh so very protected.

Spray sunscreens for example are just about useless, as are those solid stick applicators. They only get a fraction the amount you need for the rated protection. The biggest issue with sunscreen relates to companies selling sub par "convenience" slop, often right beside their other products some of which might actually be half decent.

[pazimzadeh]

Sure that’s a theory, but hasn’t been proven. If I recall, the study showed that heavy sunscreen use amongst sunscreen users was associated with higher cancer rates.

Secondly, if sun exposure is really that bad then how do you explain why most skin cancers are on the trunk and thighs rather than more exposed areas like hands and arms?

The simplest answer is it’s not sun exposure that’s bad but sudden high exposure after non-exposure (repair mechanisms can’t keep up with damage).

Not sure why I’m being downvoted. I guess there’s a lot of sheep among us. If anything I said is incorrect, please show me the evidence.

[piguin]

The arms represent very little surface area: https://wikem.org/wiki/Estimating_body_surface_area

A critical factor for doing a screening is how many bad burns you've had on the chest and back which would probably be similar to many times the burns on the arms in terms of surface area x added probability.

[pazimzadeh]

I like the idea of checking for that, but not sure the numbers add up.

Anterior head + legs + arms = 31.5% Anterior + Posterior torsos = 36%

> which would probably be similar to how many times the burns on the arms in terms of surface area x added probability

I disagree, my whole point is that frequent low/moderate exposure (such as arms) reduces the chance of burning during high exposure

I looked up the number, and after normalizing by surface area it looks like the skew towards torso is only for basal cell carcinoma (BCC) not (SCC).

https://jamanetwork.com/journals/jamadermatology/fullarticle...

For melanoma the trunk was the dominant site in men, while the legs were the dominant site in women

https://pmc.ncbi.nlm.nih.gov/articles/PMC2939095/

Unfortunately, that I know of there are not many studies that compare 'frequent low/moderate exposure followed by high exposure' vs 'very low exposure (high sunscreen use) followed by high exposure'

Here is what I found:

1. https://pubmed.ncbi.nlm.nih.gov/9335442/

  These results show the specificity of the positive association between melanoma risk and intermittent sun exposure, in contrast to a reduced risk with high levels of occupational exposure.

2. https://www.nature.com/articles/s41598-026-48477-4

  Both the low-intermittent (HR = 1.26; 95%CI = 1.17–1.38) and high exposure groups (HR = 1.13; 95%CI = 1.01–1.26) had higher rates of melanoma than indoor workers. 

  The low-intermittent exposure group had elevated melanoma rates on the arms and trunk (body), while the high exposure group had an elevated rate on the head and trunk.

Digging into the data, the moderate exposure group had no detectable increase at any body site and a weak suggestion of lower risk (not statistically significant):

  Head: 0.99; Arms: 0.95; Trunk: 1.00; Legs: 0.90

Plotted: https://imgur.com/a/HBp8SnH

Why would the low-exposure group have a higher rate on the arms and trunk? Could it be because when they do go to the pool/beach, their arms are not protected? Whereas in the high exposure group, their arms are protected due to everyday exposure, but their trunk is only exposed when they go to the pool? Then again, you would think the low-exposure group would also have high trunk incidence, so there might be some confounding factors like ethnicity/behavior/dress.

Anyway, hopefully I convinced you that it's not as simple as more sun = always bad.

[piguin]

My point is more that you are fishing for confirmation of your theory instead of answers that fit the data.

High sunscreen use (assuming rational choices for when to use it) and left arm truck driver risk is very consistent with a microeconomics model of UVR x filter factor on each cell determining probability for any given cell.

Some other problems with a study of Ontario work exposure are covered in the study itself. In essence this is low exposure compared to leisure time sun bathing that may be more desirable depending on work environment.

[pazimzadeh]

> you are fishing for confirmation of your theory instead of answers that fit the data

If you say so.

> left arm truck driver risk

Truck driver sunlight exposure is spectrally different from ordinary sunlight. It is all UVA, over many hours a day. To repeat myself, moderate exposure to preferentially UVB likely yields the highest reward/risk.

> a microeconomics model of UVR x filter factor on each cell

I'm not quite sure what you mean by the economics stuff but in addition to not mentioning the UVA/UVB difference, your model doesn't seem to take into account host repair pathways, which actually require some moderate damage to be activated, but are overloaded by too much damage (similar to the effect of exercise on the body).

Enhancement of UVB-induced DNA damage repair after a chronic low-dose UVB pre-stimulation

https://www.sciencedirect.com/science/article/abs/pii/S15687...

> Some other problems with a study of Ontario work exposure are covered in the study itself.

Some other potential problems, sure, along with a mention of potential benefits of vitamin D from optimal sunlight levels.

Since sunlight is associated with a lower risk of almost all cancers (including recovery from melanoma), not to mention autoimmune diseases, and skin cancers are amongst the easiest to catch early and to treat when caught early, it is very irresponsible to argue against the benefits of sun exposure. The idea that every additional unit of "UVR" carries an identical marginal risk is especially harmful.

[piguin]

If we live long enough to reproduce and usually impart some guidance to offspring evolution has done the optimization it will do. You seem to want to believe in a lot of systems that may sort of work but really we are not right to expect that every dose of UVR isn't a roll of the dice for a game plan that works out to less than 30 years in the sun while having hair or taking reasonable precautions for having no hair.

Trying to hide low but perpetual UVR risk for people who think they are going to be immortal is counterproductive compared to fixing the delusion that would make someone avoid life expecting to get more of it.