I know it must sound nuts to suggest this during such a sultry summer, but I'm becoming more convinced. And not because of green / New Urbanist arguments where we're told that the carbon footprint of A/C is yet another reason to walk or take mass transit.
Human beings did not evolve in a world with A/C, and we're more adapted to the hotter summers than the colder winters that we have here in America. You may think the heat or humidity are bad, but you'll survive, even without technological fixes like fans, light and loose clothing, or sunscreen. Try surviving a winter without a heater of some kind, clothing, bedding, etc. At first glance, A/C looks pretty unnatural, and because natural selection tends to keep us adapted to our environment, we may be messing around with something we shouldn't by living in continual A/C spaces.
How? I suspect we're weakening our body's system for maintaining temperature. We have a certain temperature that our body prefers to be at, although the environment may push it above or below that point. Our system has to adjust it back to where it wants to be. Changes in weather and climate seem to follow a power-law distribution, where most shocks to our temperature are small in intensity -- like a gentle breeze -- and higher-intensity shocks are rarer though still present -- like a scorcher of an afternoon. It's this type of shocks that our body was meant to deal with -- lots of minor deviations from our preferred temperature, but also a small number of quite large deviations, maybe only once a month or year.
As we're growing up, our system gets training in dealing with those high-intensity shocks, so that we deal with them pretty well by adolescence or adulthood. We must deal well with the smaller shocks even earlier because there are so many more of them, requiring less training time. But spending the summer, and by now the entire year, in an air-conditioned environment with its constant temperature, we lose the strength that comes from exposure to and eventual mastery over small and large shocks to our temperature. Then during those times when we cannot turn on the A/C -- say, walking around the block -- our poorly trained system can't cope and gets more overheated than it should, we'll get more irritable on hot days than we should, and we'll be more tired than we should. With plenty of training to deal with shocks, though, we'd do just fine.
A very close analogy can be drawn to using heavy sunscreen from childhood onward. By using sunscreen, you fail to develop a tan -- a tan that would protect you from further sun damage. Your skin now faces no outside shocks; it is protected in a constant environment from the vagaries of how much sunshine there'll be this week and the next and the next. But suppose one day you run out of sunscreen yet must go outside for awhile -- now that it's mid-summer and you've built up no defenses through training, your skin is going to get zapped.
Obviously it would be foolish to suggest the exact opposite approach -- maintaining a constant high temperature or baking in the sun all day long if you have white skin. That lack of variation in exposure levels would also be harmful (more so). Again, the shocks should be mostly on the light side, a handful at the next level up, and only some rare ones at the highest level -- but these should be there. Our sweating system and our instinct to stay out in the sun for awhile but then seek shade must be better ways of maintaining our body temperature, since they are the results of hundreds of thousands of years of natural selection, not some man-made gizmo like A/C that only became common within the past two generations.
(I realize there are other potential health issues with A/C, like bacteria growing in the system and being spread through the house if the filters aren't changed. But these are fixable problems. I'm talking about problems that are inherent to any attempt to keep our surroundings constantly cool in temperature.)
What else do we lose by not sweating? Although we may not do it as much as other species, humans send chemical signals through our body odor, facilitated by sweating. Just google "sweaty t-shirt" and you'll find links to the cottage industry of research studies that show how we factor in someone's underarm sweat unconsciously when deciding if we'd like them for a mate or not. There was a similar study done in the 1970s showing that females who were ovulating had more pleasant-smelling underwear. (Psychologists, huh?) Who knows how widely we use body scent to communicate things about us to others? By stopping ourselves from sweating, we cut off this line of communication among us.
The final reason to want to sweat may seem superficial but is actually deeper: there's nothing like a nice coat of sweat to make your skin glisten. Not necessarily while you're sweating, mind you (although there too), but after your skin has absorbed the water and various solutes that sweat contains. If you've ever seen or touched your skin -- or someone else's -- after having been through a sweaty ordeal, you know that it looks more glowing and feels tighter and bouncier. It's hard to mimic that with common man-made moisturizers -- it must be something about the precise mix of solutes in sweat that give the skin itself a different look and feel, or perhaps this mix of salts refracts light in a particular way (like grains of sand that make a shoreline sparkle).
Our minds evolved to find attractive, among other things, whatever would honestly signal good health in another human being. Skin glistening from sweat signaled that our system for body temperature maintenance was in good working order -- neither profusely gushing sweat nor holding back altogether and making us fatigued from overheating. It also showed that we were vigorous enough to go around doing things that make you sweat -- being athletic, hunting, dancing, performing manual labor, etc. -- which a sickly person would not have the strength to do.
Since A/C only became widely adopted by the end of the 1980s (it increased after that but at a slower rate), if you watch any movie from the '80s or before, you'll see that their skin looks a lot more glowing and bouncy than in movies from the '90s or 2000s. There are other reasons for that, like their more animal-based diet rich in vitamin A and relative lack of sugar, but another reason was just good ol' sweat. During the past two decades, it looks drier and more matte.
So what to do? Well I'm getting by fine without any A/C whatsoever. I have a fan in my room that I keep on low and that I only train on my body every now and then when I feel like I need a cool breeze; otherwise it's pointing somewhere else to circulate the air. Leave windows and doors open, too. Roll the windows down in your car -- that's how it used to be done, plus the A/C cannot replace the feel of the wind whipping through your car. I only turn on the A/C for minute when I first get in just to cool off the steering wheel that's been baking in the sun. When you're just in your room or otherwise by yourself, wear less clothing -- nothing breathes better than nothing. I'm typing this in just my underwear, and I don't feel weird or uncomfortable. Hell, it brings me closer to my hunter-gatherer and pastoralist past.
Most importantly, spend more time outside of buildings. Unless you live in a place with unbearable humidity, the only place you can find stifling stuffiness is inside a building. Again, human beings did not evolve in stone or otherwise insulated housing, so we are not well adapted to living in enclosed structures for most of the day. Even with no breeze whatsoever, it almost always feels better in the fresh air than holed up inside, especially when the sun is going down. If you've already had enough sun, you can stay outside as long as you find shade -- not hard to do.
This case illustrates a general point I've been trying to make lately about the dangers of overprotecting ourselves from shocks, inspired by EconTalk podcasts with Arthur De Vany and Nassim Taleb that I linked to elsewhere. By pursuing momentary comfort -- say, by having the A/C on or wearing sunscreen whenever we go out -- we increase our risk of worse outcomes than if we'd trained ourselves to various intensities of shocks. Over the long-term, we find ourselves overheated just after walking out to the mailbox on a warm day, or find a blistering sunburn after a single afternoon of sunshine when we forgot the sunblock.
In earlier times, parents and friends would tell us to "suck it up," or "take it like a man" when we were slightly uncomfortable in the present, knowing that this would pay off over the long term. And they were right. Our more hedonistic practices have sabotaged our well-being and our attractiveness to others.