[ Question ]

How many micromorts do you get per UV-index-hour?

by capybaralet1 min read30th Mar 20217 comments



I'm trying to get a good estimate of the risks associated with sun exposure.

I'm assuming things scale linearly (the UV index units, which need a name ("UVees"?) are linear).

This may not be a good assumption, but it seems somewhat likely that it would be within the range I most care about (significant exposure, but not enough to get burnt -- if I'd get burnt, I'll certainly cover up or wear sunscreen).

I know sun exposure is a major source of skin cancer risk, but I'm not sure how much of that is coming from people who have tons of exposure, and how much risk a moderate level of exposure actually brings.


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About 20% of Americans develop skin cancer during their lifetime, and the 5-year overall survival rate for melanoma is over 90 percent. Taking this as the mortality risk, i.e. ignoring timing and varied risk levels, it's a 2% risk of (eventual) death.

But risk of skin cancer depends on far more than sun exposure - and the more important determinant is frequency of sunbathing below age 30. Other factors that seem to matter are skin color, skin response (how much you burn,) weight, and family history of cancers.

You're talking about exposure to ionizing radiation.  This means there is a chance each UV photon that hits exactly in the right spot will cause permanent DNA changes that eventually lead to cancer.  So the right answer when asking how many invisible bullets you want to be shot with until one is fatal is "as few as practical".  

You can get vitamin D from a tablet.

Now, yes, a lack of sun may cause depression and you die from that, or other malfunctions, and most humans don't die from skin cancer.  

So I don't see it in terms of 'micromorts', I see it in terms of 'the outdoor activity had better be really fun' and "i'm going to protect myself as much as practical".  

Hanging out on a beach with potential mates?  Worth the risk.  Mowing or weeding your lawn?  I'm gonna wait til dusk or use a lot of protective gear.

each UV photon that hits exactly in the right spot will cause permanent DNA changes that eventually lead to cancer

Pretty sure this is incorrect. It's not the damage that causes cancer, but the failure of the body to heal/repair it. Such failures can be caused for example by you being very old, and therefore healing slower, or by getting a sunburn (= too much exposure in a short time, overwhelming repair capability).

I think the most important thing here is that things scale very much not linearly.

See also this, which argues/claims that more sun exposure (wi... (read more)

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Note that exposure to UV from sunlight has benefits as well as costs (e.g., vitamin D production). I personally wouldn't want to bet heavily that in the "interesting" range the effect is close to linear, nor that the linear term has the sign you think it has.

Oh yeah, sorry I was not clear about this...

I am actually trying to just consider the effects via cancer risk in isolation, and ignoring the potential benefits (which I think do go beyond just Vitamin D... probably a lot of stuff happening that we don't understand... certainly seems to have effect on mood, e.g.)

Might depend on your polyunsaturated fat intake: https://pubmed.ncbi.nlm.nih.gov/29636341/

Looks like just correlations, tho(?)
I basically wouldn't update on a single study that only looks at correlation.