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Skin exposure to UVB light induces a skin-brain-gonad axis and sexual behavior


Well, this is oddly personal for hackernews but what the heck. This is pretty interesting to me. I’ve been living outdoors for the last 12 months, and I’ve noticed some significant changes in libido. It’s been on my mind quite a bit (not only for the obvious reasons but also wondering why this is happening to me). There’s a lot of factors of course, going from a mostly sedentary indoor life to a mostly actively outdoor life but this is fascinating. My SO is much more careful than I am with UV exposure and hasn’t seen the same change but again, too many factors to control for in this sort of anecdotal experience.


Interesting nonetheless, thanks for sharing!

Slightly related: I've decided to stop using suncreen altogether for day-to-day sun exposure. My mood and overall sense of happiness increased significantly – in fact, it seemed to have helped more than my antidepressants ever did. (My libido did not increase but my antidepressants are pretty much libido killers.)


I don't put on sunscreen unless I know I will be outside unexposed for over an hour while the UV index is 5+. If I can wear a hat and long sleeves or know there will be shady spots, I still avoid sunscreen. I rarely get anything close to a burn and I believe this is probably healthier than the religious screen use that everyone seems to recommend.


Got to watch out with sunscreen too. Many brands have ingredients that can pass the blood brain barrier.


Shit like what??


So has water


I’ve been seeing more and more evidence that we may not be getting enough UV exposure in general in the US. Vitamin D production is big, but what fewer people know about is nitric oxide which is also sythesized from UV exposure. It is a muscle relaxer that lowers blood pressure. It would undoubtedly have a positive effect on your mood.


.. and your dick. Raising NO is the mechanism of action for Viagra.


I try to keep full spectrum light bulbs in as many rooms as possible within in my house, which also helps a bit, along with going outdoors as much as possible and supplementing vitamin D.

There is a whole lot of new conflict world wide out of the isolation and conservation that recent pandemics have caused. It's been a really frustrating missed opportunity by social and dating apps that they don't better help people to navigate social communication, scientifically based health advice, and relationship building/improvement with all the human isolation that is occurring and growing fast.

The term gonads though has always triggered Beavis and Butthead giggles for me ever since high school.


There is a popular theory out in the fitness world that seed oils inhibit our skins ability to resist sunburns. Personally I’ve found it to be true.


I haven't noticed any changes since I got back into hiking but I'm careful with the sunscreen--I live in the desert where the sun is brutal, any mistake is liable to result in a burn.

I have been seeing many hints recently that UV might be good for us in moderation but determining how much one is getting is problematic.


Bremelanotide, a medication used to treat low sexual desire in women, has skin hyperpigmentation as a side effect. Could there be a connection?


Interesting article. This sentence was interesting:

  Very early in the process one of the scientists, Mac Hadley,[15] who was conducting experiments on himself with the peptide melanotan II, injected himself with twice the dose he intended and experienced an eight-hour erection, along with nausea and vomiting.[13]


I don't understand. Sounds like a typical Saturday night to me.


My bodybuilder friend used to inject Melanotan II (?) and would get super tan after just a couple days of summer. He'd also get wild random erections while on it. It's an anecdote, but the post title instantly made me think of that.


There’s a few decades of small studies confirming this: from 2000:


"The questionnaire we used measured romantic passion, rather than physiological/sexual passion, due to institutional review board (IRB) ethical concerns regarding sensitive sexually oriented questions."

Curious about this. I understand ethical boards for psychological blind studies and such, but for questionaires?


Yes, it’s stupid. IRBs today are, on net, more of a detriment to science than a benefit. When they block a stupid voluntary questionnaire for being “unethical”, just imagine how much other useful science is not being done, because of concern lack of ethics of a similar grade.


IRBs look like a net detrement to most studies because they are a mechanism to prevent really bad/unethical experiments in the far tails of distribution.

If those extreme studies were to happen at a non suppressed rate we would be asking for IRBs and talking how science can't regulate itself.

So IRBs might be effective but they suffer from the prevention paradox.


Would be interesting to see their reject pile.


IRBs are a net negative because really bad/unethical experiments are done with no oversight by private entities. Their only purpose is to keep ethicists employed.


I was supposed to get an IRB review for a graphics experiment I did in undergrad where I showed people static, non-animated optical illusions on a computer screen and asked them some questions about whether or not it gave them the impression of hills. (This was, like, 20 years ago.)

Apparently there was some concern about inducing epileptic seizures. Not that there was any evidence that optical illusions, on their own, separate from the flickering of the computer screen, could cause seizures. But someone had the idea and then it couldn't be un-un-boxed.

The IRB submission process would have been too long to finish the study by the end of the semester (by the time I found out about it). So I just... didn't tell anyone I had already posted the demo online, before I ever even learned that IRB existed, and had a bunch of people on a game development forum on which I was a regular go through the study.

In my case, it was super low stakes. I mean, people into game development are subjecting themselves to the dodgy apps all the time. But when I tell this story today, there are two types of responses: those who have done academic research and laugh at my story, and those who haven't and start crying about "HuMaN eXpErImEnTaTiOn!!!"

I should start putting that on my business card: "formerly engaged in unlicensed human experimentation."

Who am I joking? I don't have business cards anymore. It's going on my Twitter profile.


There's similar issues with computer security and having projects reviewed before being shipped, with the classic story of people avoiding review because they didn't think they needed it at the start of their project (not that they're qualified to determine that) and by the time someone told them about it, it was "too late" and they'd miss important deadlines by going through the requisite review.

The only sane solution I've seen to that is to make everything go through security review, even if the review is a simple "we don't need to review this." If everyone knows everything needs review, it makes it very hard to forget about it and incentivizes people to involve security folks with their projects ASAP in the hopes of getting review done early on / avoiding being blocked by it.

You'll always need exceptions to the rule, so you can have some sufficiently high up VP or similar sign off on releasing things without review (and with the caveat that it's still going to get reviewed, it just won't block release), but that's a lot easier to manage than dealing with random developers deciding it for themselves.

It also helps a lot to have a culture where developers learn about security too, but just like researchers and ethics, they'll have perverse incentives to downplay/ignore risks so you still need other, differently incentivized people, to enforce "checks and balances."

It sounds like IRBs are not designed to review all or even most (animal?) experiments and I think that's unfortunate. It seems like a win for everyone if we get better ethics coverage.


classic feature creep + bureaucratization (so it's now done by a special class of IRB administrators, not really by peers, etc)


I would normally be a bit skeptical of anything published by CSPI.


Given that American universities now routinely have a lot more administrators than teaching staff (still very untypical elsewhere in the world), wouldn't you at least agree that the bureaucratic bloat is real?

This is, after all, what the students are paying in their tuition, which is becoming a major burden on the American middle class.

(Ironically, "tuition" as a word promises that the money is mostly spent on teaching, not on administration and amenities.)

There is a strange reluctance on the American liberal left to criticize greediness in academia or even acknowledge that such thing exists. Politically, I get it, the academia is overwhelmingly liberal-left, so there is an instinct not to alienate it. But there surely must be some upper bound to the growth of tuition costs, after which the burden becomes unbearable.


Why? Do you care to elaborate, or do you prefer to just cast vague aspersions?


Sounds like the Iron Law of Bureaucracy is at it again.


Could be a signaling behavior to encourage spring births. Does UVB peak in the middle of the summer? 9 months later is probably the best time to birth a child for that child's success.


The study measures the effect in mice. Mice have a gestational period of a few weeks, so that's probably not it.


It works in mice as well, they just don't have to wait a winter cycle for gestation. They basically give birth instantly after mating. They would be making _less_ babies during the low UV months and peaking during the summer time when the living is easy.


Gabriele Doblhammer and James W. Vaupel concluded that "month of birth influences adult life expectancy at ages 50+" in their paper [1] in the Proceedings of the National Academy of Sciences (PNAS).

They tracked for 30 years the mortality of all Danes who were at least 50 years old on 1 April 1968 (about 1.4 million people born before April 1918). They also analyzed about Austrians with known birth dates who died between 1988 and 1996 (about 700,000 people born before 1947) and native-born Australians who died between 1993 and 1997 (about 200,000 people born before 1948).

They found in Denmark and Austria that "adults born in autumn (October–December) live longer than those born in spring (April–June). The difference in lifespan between the spring and autumn born is twice as large in Austria (0.6 years) as in Denmark (0.3 years). ... We found the pattern in the Southern Hemisphere to be a mirror image reversal of that in the Northern Hemisphere." British born Australians were statistically closer to the Danes and Austrians.

Their analysis eliminated three hypotheses for these observations: seasonal distribution of deaths, social factors related to seasonal distribution of births, and differential infant survival. Their analysis and other studies of birth weight data led them to conclude that "seasonal differences in nutrition and disease environment early in life [in utero and infancy] could explain the relationship between month of birth and adult lifespan." Over the years, winter and spring nutrition has improved, so "the relationship between month of birth and lifespan seems to be stronger among the older birth cohorts than among the more recently born."



Hypothesis: people conceived from impulsive sex on Midsommar are more likely to have un-attending and less-caring parents, and possibly inherit lower self-control traits.


That seems possible but also more directly winter may be a bad time to start a pregnancy.


Avoiding the birth of a child right before winter would be advantageous for its survival… winter being (on average, not all regions/locales obviously) the hardest month to survive evolutionarily speaking this would be a beneficial trait and be likely to stick around. Ideally you want your early hominid babies at the end of winter through spring and summer so at worst they are though the first few fragile months that put the most drain on the mother, before the harshest winter weather sets in.

While not globally consistent due to regional weather differences it makes sense for there to be a broad average seasonal benefit.


Except those “early hominid” lived in Africa, which isn't known to be the place with the harshest winter. And the fact that humans living in temperate climates and humans in tropical areas belong to a single species makes me believe that adaptation to winter wasn't that big of an evolutionary factor.


As far as we know, humans are a tropical species, which means reasoning about summer and winter is likely to be more misleading than anything.


Doesn't it seem like a common misconception that evolution takes eons? Without being an expert, it seems plausible that we've adapted biologically since venturing out from the tropics.


The most obvious adaptation since venturing from the tropics is reduced pigmentation to adapt to less intense UV radiation. Nose shapes are also influenced by climate.

The idea that we stopped evolving sometime before we spread over the globe is obviously false, with the number of adaptations that are plainly observable on the outside.


But that "we" includes people that didn't venture out of the tropics, who presumably are impacted the same way by UVB, which if true would refute the hypothesis.


> Humans are essentially tropical animals and are not equipped to deal with even mild cold. That we can live in cold climates is a result of behavioural adaptations such as wearing appropriate clothing and building shelters.

So this is why I hate winters and don't complain when it's 90 degrees Fahrenheit outside.

I would wear a jacket or hoodie in the middle of summer because of the office AC.

I need to move to Key West.


I was thinking along the same lines but also harvest for fattening up.


One of the referenced papers [0] concerning addiction to UV light (in rodents) is fascinating as well..!

“UV light is an established carcinogen, yet evidence suggests that UV-seeking behavior has addictive features”

“Opioid blockade also elicits withdrawal signs after chronic UV exposure”



What might be going on here is that the UV induces radiation damage, which leads to endorphin release as part of the body's response to injury and pain. I have experienced this effect myself at times after getting a sunburn; the endorphins blocked the pain entirely and it was moderately euphoric. I know how dangerous sunburns are but if I was a rodent I would likely seek ways to repeat the experience.


Implying that a primary causal factor for globally-declining birth rates could be... increased adoption of sunscreen, leading to decreases in libido?

(I'm only half-joking; the countries that are most obsessed with keeping skin white — and so are likely the highest sunscreen users — are also the countries with the lowest birth rates.)


I don't get how reduced UV exposure is supposed to be more attributable to sunscreens than to office labors.

Most industrial materials block roughly 100% of UV rays, except viewing windows which allows as much as 1%. Therefore, just staying in any modern building alone cuts down UV exposure by 99% at very least. There is absolutely no way some translucent face painting does that.


People have been working white-collar jobs indoors behind UV-reflective windows for 50+ years now. Birth-rate decline — especially to below-replacement levels — begins much more recently than that; and is only happening in certain countries.

The set of countries experiencing birth-rate decline is not 1:1 correlated with the set of countries with high/increasing white-collar employment; but, AFAICT, it is 1:1 correlated with the set of countries that have strong avoidance of tanning / strong interest in skin-whitening.


>but, AFAICT, it is 1:1 correlated with the set of countries that have strong avoidance of tanning / strong interest in skin-whitening.

I'm not seeing that. The countries that are most into avoidance of tanning are probably in Southern Asia, or Asia in general. Their birth rates are not that low, with the exception of Japan, S. Korea and Taiwan.


Here is the evolution of the share of blue collar/white collar jobs [0] vs the evolution of fertility rate [1]. I am curious to hear your conclusions from that !




Isn't it a common phenomenon that smarter people have fewer children? Once you achieve high education people are more strategic about when, or if, to have children and how many.


> There is absolutely no way some translucent face painting does that.

Wow what a dismissive comment to chemistry and cosmetics.

Just for fun, try take a pic of yourself with a UV camera (or just UV light with some phones), and you'll see it's translucent only to the visible spectrum:


One thing I've recently become curious about, is whether the "UV pigments" in sunscreens are color-fast or not; i.e. whether getting sunscreen on clothing gradually tints the clothing darker when seen in ultraviolet, in the same way that getting throwing a non-colorfast red shirt in with your whites will gradually tint them red.


The Sun Protection Factor(SPF) is defined "a measure of the fraction of sunburn-producing UV rays that reach the skin" when applied as instructed and only over a defined period, usually 2hr[1]. That means there is twofold difference even between a pane of glass(<1% whole body) and correctly applied sunscreen(~2% for 2hr @ SPF50), before taking walls into accounts.



> the countries that are most obsessed with keeping skin white — and so are likely the highest sunscreen users

Isn't it rather more about avoiding skin cancer?


While American and European sunbathers tend to seek the perfect tan, many Indian and East Asian women avoid it at all costs, through sunscreen and a whole bevy of skin-lightening products:

Such standards of beauty are quite old and largely predate Western colonialism. My impression is that they were often linked to caste or class, where higher-class people spent more time indoors while lower-class workers spent more time out in the sun.

This cultural difference is the source of much amusement for the Indian spouse of my European coworker. When they vacation in Europe all the ladies on the beach want to tan, and when they visit India it’s the other way around.


> My impression is that they were often linked to caste or class, where higher-class people spent more time indoors while lower-class workers spent more time out in the sun.

I'm no expert on the topic, but i heard people refer to this sort of social symbol and discrimination as "colorism".

For anecdote, in France, "sang bleu" (blue blood) used to refer to the nobles and higher classes, as they didn't work the fields, and their thin and pale skin let see through the blue-looking veins. From what i hear, it appears before the revolution this biological distinction was formally racialized: the higher classes with their never-sighted "blue blood" was another "race" as the lower peoples whose spilled blood we could confirm was red.



In many caste-esque societies, having a darker tone is a sign of having to work outside, thus of lower class.

This happens a lot in the Philippines, for example. With a ton of skin lightening products.


Cultural expectations on tanning come down to signs of wealth.

Industrialized societies most work is performed indoors, most people only tan during leisure time. Thus a tan is an indication of having leisure time and is looked upon positively.

Societies that are not industrialized most work is performed outdoors, leisure is generally indoors. Thus the absence of a tan is an indication of wealth and is looked upon positively.

Note that this lags behind reality, many places have industrialized but their perception of tans is still negative. My wife is Chinese and I sometimes joke that she's half-vampire because of how sun-avoidant she is.


There are a whole host of benefits associated with sun exposure that are reduced by wearing sunscreen.

“Avoidance of sun exposure is a risk factor of a similar magnitude as smoking, in terms of life expectancy.”


I'm open to the argument that it's wrong/irrational, but I would wager that - at least in the USA - people wearing sunscreen are doing it to avoid skin cancer more than to avoid tanning.


I am not certain how much credibility this publication deserves.

It's not scientific by nature, it focuses on outdoor activities, which is only a tangent topic, the author has no bio, there is little to no bibliographic references.


I use it to avoid burns?


If that’s the case then it’d come as a relief. But I doubt it. Realistically the fact wage to housing/health/education/childcare is a bigger contributor.


Provided how people apply sunscreen, I doubt it. Not exactly translatable, but there was no effect on vitamin D levels in people using sunscreen:


It is probably birth control in the water supply that are causing birth rate declines.


That has been thoroughly studied and debunked. Just one example of many:

Add to this the fact that less than 1% of the estrogen in the water supply is from The Pill.


Yes. I'd be more worried about estrogen in meat.


That paper used predicted estrogen instead of measuring estrogen. I wouldn't say it has been studied at all based on that link.


> (I'm only half-joking; the countries that are most obsessed with keeping skin white — and so are likely the highest sunscreen users — are also the countries with the lowest birth rates.)

Obsession with keeping skin white is not something I normally see associated with South Korea, Singapore, or Bosnia and Herzegovina.


Obsession with keeping skin white has been a major trend in Korea for a long time, have you seen all the weird hats and face masks that ajummas wear in order to reduce sun exposure?


Can't speak much for Bosnia but in most of South East Asia it's nigh on impossible to find any body wash, sunscreen or moisturiser without whitening products added.


Have you ever tried to buy sunscreen in Asia?


Question: how does sunscreen affect these outcome ? I have been in a UV-high indexed area for over 2hrs a day under sun and wondered if applying sunscreen everyday as I have to exposed parts such as arms and legs have negative consequences since all of them have benzene. Now this seems to be another reason for not doing so?


Not directly answering your question but related: "early sunscreen formulations were disastrous, shielding users from the UVB rays that cause sunburn but not the UVA rays that cause skin cancer. Even today, SPF ratings refer only to UVB rays, so many users may be absorbing far more UVA radiation than they realize."


How can you know if it does both? Look for UVA on the bottle?


Zinc Oxide does. Kid sunscreen is almost always zink oxide to prevent hormone disruption from the nasty stuff they put in adult sunscreen.

The term "broad spectrum" is used to denote UVA/UVB protection in the US, and is an FDA-regulated term.


The UK - and I presume Europe - has a star rating for UVA protection in addition to SPF. Some details here:

Tl;Dr - you want minimum 5-star 30 SPF for your daily cream.


Look for PA+++ ratings. You might have to buy sunscreen made outside the US, such as sunscreens made in Korea.


UVB exposure -> p53 activation -> downstream sex hormones upregulation is hypothesized to be mechanism, so sunscreen that blocks UVB will probably reduce the effect.

This study is part of an interesting trend I'm seeing of studies finding beneficial health effects to well timed, full spectrum sunlight exposure. The circadian benefits of seeing early morning sun every day (and darkness every evening) are well known. What's more surprising is that even UV exposure is not purely negative, and in the context of sunlight in moderate amounts (not to the point of acute sunburn) may be beneficial for health: finds that high intermittent sun exposure actually decreases melanoma lethality. I.e. those who avoid the sun die more from melanoma. found in a study that followed 30k women over 20 years that more sun exposure was associated with reduced all cause mortality. I.e. those who avoid the sun, apply more sunscreen die more in general.


Under these conditions, I would recommend a UPF 50 garment, like Columbia PFG Terminal Tackle Hoody (but I have seen George aka Walmart for $10). I think this is safer than applying chemicals. Also sunscreens in the US are far behind the EU and Asia


Benzene? I really doubt that. Benzene is almost banned even at labs because it’s so insidious.


Not all sunscreen have benzene, but there have been some recalls because benzene had been found:


This isn't big news at all.

Melanocyte-stimulating hormones have been known to stimulate sexual behavior since forever. Melanocortin receptors directly modulate sexual behavior.

Melanocyte-stimulating hormone production is boosted by from inflammatory effects of UV damage. This has been known forever, too.


> boosted by from inflammatory effects of UV damage

That wording supports a notion that the boosting is to encourage the most essential activity of a species—reproduction—in the face of potential harms that may shorten the opportunity for that activity (cancer-induced final exit).

That said, I’m aware of counterarguments to the simplistic takes on “sun bad” messaging and think they have merit. Not trying to open a debate on the latter, just clarifying that I’m not trying to grind an ax with the first paragraph.


That seems a bit simplistic of an interpretation when there are no similar effect for dehydration, hunger, loss of a limb, or other potential harms.

Many animals are seasonal. And extra sun exposure might indicate a good time to mate (spring/summer)


Your example harms have an immediate effect. Sun exposure usually does not.


Sun exposure causes a severe inflammatory exposure for me. Spent a day at the beach and it was 7 months of burning nerve pain before I got it calmed down. Side effect of autoimmune Sjogrens.

I don’t go out if UV is above a 2 anymore.


There's no way that we evolved to chemically respond to an effect that takes fifty years to happen.


Evolution is a long tail game. Over eons, any mutation conferring an increased likelihood of sustainable reproduction can “win”, including this one.




Thats what came to my mind too.


Anyone who has taken Melanotan-2 or PT-141 could tell you this ;^)


Thank you for the additional info. I certainly found it to be big news.


Interesting. A possible mechanism for the legendary passion of people from "hot blooded" countries?


If anything, people who originate in cold climate countries visiting hot-blooded countries would receive more UVB due to less skin melanin, and thus be more hot blooded than the natives of hot blooded countries when interacting with them, and vice versa, so that would't explain the association.


Ah, the ‘Brits Abroad’ phenomenon finally explained.


Something that fascinated me with Russians is how they go out of their way to get every bit of sunlight. I mean, they act like sunflowers, even standing to face the sun and open their arms on the beach, and orienting themselves towards it. They'll go to the beach at ungodly hot hours and stay under the sun, in Tunisia, during summer!

It is amazing because I'm really dark and dark skinned, I'm also native of the region (Algeria), and even then, I'll protect myself and stay in the shade because I'll get sunburnt very easily if I don't take precautions. They're fair skinned and they're not as cautious. It's just incredible.


All that's racist is new and progressive again.

I'm still waiting for someone to explain the difference between colored people and people of color.


The melanotan peptide's effect on melatonin production and libido is super interesting considering this finding


Or maybe tan people just look more attractive and get more attention


Or just people that work in field don't watch so much porno.


I could tell Aussie girls were different.