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Ah, fall. Crunchy leaves, warm sweaters, chilly weather.

And, of course, pumpkin spice. Sooo much pumpkin spice. From candles, to yogurt, to Oreos, it's everywhere—especially in our lattes.

The craze might seem a little bit over the top, but it actually makes total sense psychologically. So far, there hasn't been any specific research on what makes pumpkin spice so compelling. But psychologists do have some ideas about what might be going on.

Turns out, pumpkin spice is basically the perfect brain puppeteer. First, there's the sugar. In case you missed it, sugar is super addictive.

A review from 2013 found that in some ways it can be more rewarding and addictive than cocaine, and hoo boy, is there a lot of it in a pumpkin spice latte. Sugar, that is. Not cocaine.

At least, that's what they tell us. A medium-sized pumpkin spice latte can have about 48 grams of sugar, which is a quarter of a cup or about 37 gummy bears. So yeah… if you love your PSLs, you might not want to think too hard about that.

And it's not just the lattes. Pairing that distinctive pumpkin spice flavor with sugar over and over in baked goods and drinks teaches our brains that pumpkin spice equals reward. That's part of why you crave it.

Of course, that can't be the whole explanation— peppermint mochas and caramel apple spice ciders have a ton of sugar, too. Psychologists think some of pumpkin spice's popularity may have to do with social conformity— our tendency to change our beliefs or behaviors to match those around us or in our culture. While some of your friends might judge you if you don't buy a pumpkin spice latte the second they're available, social conformity goes way beyond direct peer pressure.

Simply seeing everyone else drink ‘em and tweet about ‘em and take selfies with ‘em can be enough to convince us that we want one, too. It's a pretty well-documented phenomenon. The most famous example is the Asch conformity study, where other people's responses convinced subjects that one line was longer than two others … even when it very clearly wasn't.

And psychologists have found that social conformity can also affect our eating choices. For example, in a study of 39 preschoolers in 1980, researchers found that the influence of peers could change a child's opinion about a vegetable they didn't like. And if you've ever tried to convince a stubborn kid to eat their broccoli, you know exactly how much of an accomplishment that is.

In the study, children sat at lunch tables with a few other kids who disagreed with their preferences. So a child who really liked corn but hated peas would be told to sit with kids who dug peas but weren't into corn. After just four days of seeing the other students pick peas over corn and express their liking for peas, the kid who originally said they didn't like peas would start liking them a little more.

So with everyone around you talking about how awesome pumpkin spice lattes are, it's not too much of a stretch to imagine that they're influencing your opinion of it, too. There's evidence that social pressures can also affect our buying habits. Research has shown that when we don't have objective information telling us whether to buy something, we'll usually just do what everyone else is doing.

And the way it's only offered each fall? That's another part of the brain-gaming. It's taking advantage of what's known as reactance theory, which says that we don't like when people try to limit our behavioral freedoms, and as a result, we're more likely to do things others try to keep us from doing.

And not being able to buy a pumpkin spice latte whenever we want to? You'd better believe that feels like a limit on our freedom. I mean, this is America!

So, since we can't get pumpkin spice all year round, we want it more. It might sound a little extreme. But reactance theory has been shown to explain why short-term sales or seasonal specials like pumpkin spice lattes are so effective.

For example, way back in 1966 a study showed that just telling people a certain product was out of stock was enough to make them rate it as more desirable. And another study from 1987 found that one-day sales made people more likely to buy something than three-day sales or five-day sales. So the burning envy you feel when your coworker posts that Insta of the pumpkin spice latte they managed to get a whole day early?

You want that latte so bad because you can't have it … and that's reactance. We might also love pumpkin spice so much because it's quintessentially fall. For a lot of people, pumpkin spice triggers nostalgia.

That mysterious mix of cinnamon and nutmeg drags us right back to apple picking, carving pumpkins, and baking Thanksgiving pies with Grandma. And studies have shown that those warm ‘n fuzzies can literally make us feel happier, giving a boost to our social bonds, our self-regard, and our mood generally. Which means that if pumpkin spice makes you nostalgic, you're basically buying happiness in a little paper cup.

So, pumpkin spice has our brains good and hacked. We drink it in lattes and put it in candles because everyone else is doing it, because we can't have it all the time, and because it literally makes us feel good. None of that is necessarily a problem, though.

Y'know, assuming you don't spend your entire paycheck at the coffee shop. Thanks for watching this episode of SciShow Psych! If you're interested in learning about what's really in a pumpkin spice latte— and the chemistry that goes into flavor science in general— you can watch our video about that on the main SciShow channel. [OUTRO ♪].