From metabolism to sex drive, hormones come in tiny packets that pack a powerful punch, and yet there is a lot of misinformation about these chemicals. So Randi Hutter Epstein, a doctor and medical writer, decided to set the record straight. The result is her book Aroused: The History of Hormones and How They Control Just About Everything.

Though we throw around the world “hormonal” today, the concept didn’t exist before the 1900s. In the past century, we’ve gone from not knowing what these glands secreted to selling hormonal sprays that promise to make it easier to seduce. How did we get here?

The Verge spoke to Epstein about the short history of hormones, how they were involved in the “crime of the century,” and how we sometimes give them far too much credit today.

This interview has been lightly edited for clarity.

The word and concept of “hormone” only date back to 1905. Before that, what did we believe was regulating our bodies?

We’ve always wondered what makes our bodies function correctly. There was this horrible, weird time of history in America in the late 1800s when doctors started looking at these so-called “circus freaks.” These were people with disabilities or something wrong with them, like the bearded lady or fat lady. They were being put in the circus, and at the same time, doctors were saying maybe they have some sort of glandular disorder.

It’s not like the “nice doctors” versus “mean circus people.” The circus was paying and doctors were researching them and not really helping them. So these doctors who studied anatomy for years saw glands in the body — like the thyroid and adrenal gland — but we didn’t understand what we did. Until the early 1900s, we thought that everything marched along nerves like marching along train tracks, or went through the blood like a raft going down a river, and then it’d just bang into wherever it’s needed.

Hormones are these internal secretions that come out of a gland, and they go through the blood, but they go to a specific target. This was controversial, and there were people saying it can’t be because how do they know where they’re going? I like to talk about hormones like your internal Wi-Fi because they have these signals that allow them to go to places.

Why didn’t we know about them before? What technology really changed the study of hormones?

The huge technological advance happened in the late 1950s and really took hold in the mid-‘60s and early ‘70s. It was the ability to, for the very first time, measure hormones down to the billionth of a gram. That’s like if you took a gram of salt and threw it into the ocean, and it had a powerful impact.

It wasn’t that we could sort of measure hormones before this, and then we precisely measured them. Before this, we couldn’t measure hormones at all, and it was all guesswork. This technology, which is called RIA (radioimmunoassay) has made it possible to measure things we thought too scarce to measure. We wouldn’t have been able to find HIV in blood if not for RIA. We wouldn’t be able to track cancer markers.

The other part of the story that I love about this technology is that the co-creator, Rosalyn Yalow, graduated top in her class in physics but was told to be a secretary. So she became a secretary for a scientist at Columbia, and only eventually got into the PhD program at the University of Illinois because there were some open spots because the men were gone for World War II. As she told a biographer, “They had to have a world war for me to have a graduate degree.” The rest is history. She revolutionized modern medicine, won a Nobel, and was very supportive of other women becoming scientists.

So RIA lets us measure a billionth of a gram of hormone. Do we need that level of precision? Can that really make the difference?

Yes, hormones come in tiny packets. When we say you have too much of this hormone or a lack of another hormone, we are talking in terms of nanograms. They’re potent. We’re not talking about extra pounds of hormones.

Are some more powerful than others, if that question makes sense?

The way to think about it is that most hormones don’t work on their own. There’s a chain of hormones, helper hormones, “factors.” There are different types that are super powerful and interact with each other, which is how things get super complicated, and you can have a glandular issue that has nothing to do with estrogen, but it’ll screw up your fertility because it’s all connected.

Are we still discovering new hormones?

Absolutely. In the 1990s we discovered leptin, which is the appetite hormone. We discovered it comes from fat cells, which was shocking because most people think fat cells are just blobs of butter you can remove. We’re still learning about hunger and appetite hormones, and there’s a new insulin growth factor, too. I think, in the future, we’re going to be learning more about hormones and behavior, like hormones that impact basic drives to eat, to lust, and so on.

Speaking of behavior, one fascinating part of the book was about the trial of Leopold and Loeb, and how people tried to defend them saying, “The hormones made them do it.” What precedent does this kind of approach mean for hormones and crime and law?

The trial was in the 1920s and called the “crime of the century” because it was two rich kids who murdered another rich kid. You couldn’t measure hormones then. It was speculative, and it didn’t work as far as the judge was concerned.

From a scientific perspective, we’re still looking into this. Do I think this will get people off murder? Probably not. I don’t think we’ll ever be able to say, “His hormones made him do it.” But from a scientific perspective, it’s fascinating to look at how hormones shape our behavior. And, of course, what they were doing in the 1920s, unsuccessfully, and what we’re still trying to do now, is look at what hormonal imbalances we can detect early on. And perhaps then we can treat it and make sure that we, for instance, prevent killers.

But as I’m saying these words, you can see right away this is a slippery slope. It’s like the designer baby thing. We know hormones control us, and we’d like to control them to the extent they give us quality, healthy lives, like the way we use insulin to help diabetes. But then again, how much control do we need? We don’t want to go the route of eugenics.

What do you think about the way we talk about hormones today? Like all the hype surrounding the “love hormone” oxytocin, for instance.

We simplify things too much. Too often there’s a seed of fascinating scientific discovery. And before that seed has time to blossom, there are people who glom on and extrapolate way too far. With oxytocin, yeah, it probably does have to do with human mother-baby bonding, but we’re taking a major leap to say, “You can buy an oxytocin love spray.”

There are some clues that oxytocin impacts behavior. It might augment that feeling that you have, but it could turn hate into more hate instead of necessarily hate into love. People are hoping that giving oxytocin to children on the autistic spectrum would help them, but so far, it hasn’t been very successful. So I’m not saying we shouldn’t do this research, but it’s very different from purchasing something over the counter that might not even have oxytocin in it. It could just be water.