Our weaknesses in the health arena could have something to do with the fact that medicine is insanely complicated—it’s difficult for us to discern whether two things going on in the body are related or not. And of course there’s the fact that tons of people believe and tout that home and natural remedies like vinegar cure comment ailments like colds. Google “apple cider vinegar colds” and you’ll see dozens of articles like this chronicling people’s transformative experiences.

Yet there are so many reasons to raise eyebrows at health claims based on anecdotes rather than scientific evidence. For one thing, there’s what I call real-world publication bias. Let’s say you wonder whether lemon juice cures hay fever, and you do an internet search. You’ll see tons of stories from people who swear it works. But what about the people whose hay fever didn’t ease after a lemon juice cocktail? They probably aren’t broadcasting their experiences, because they aren’t fueled by the excitement of experiencing a cure. Some may even continue to believe the remedy works and just assume they did it incorrectly. I’ve seen this on Facebook: “I drank grape juice to stave off stomach flu and I still got sick, but maybe that’s just because it wasn’t organic.” Even when the unlucky ones do report that their remedies didn’t work, their stories aren’t going to be that popular; they might not even show up on Google, because guess what? People are a lot more interested what can cure things than what can’t.

Another thing that makes remedies seem more effective than they really are: the fact that many health problems—colds, scrapes, bug bites, heartburn, headaches, cold sores, cramps—resolve on their own over time. When you try a treatment and feel better, you might attribute the resolution to your remedy, even if you were going to improve anyway. Same goes for preventive tonics: If I take Echinacea to stave off a cold and then I don’t get sick, I’ll be convinced the Echinacea worked—but maybe I wasn’t destined to catch that cold anyway. Trying more than one treatment at a time, which we often do, muddies things further. Did Vicks Vaporub really cure your toenail fungus, or could it have been the vinegar soak, or perhaps the tea tree oil you were using, too?

Last but not least, let me tell you about the absolutely fascinating placebo effect. A placebo is a sugar pill or other “fake” medicine or treatment that should not, on its own, affect a person’s symptoms. But as an anesthesiologist discovered during WWII, when he noticed that merely telling wounded soldiers they were getting morphine made them feel better, placebos can be powerful healers. Put another way: When we expect that a remedy will make us better, sometimes the expectation itself does the job. In 2016, researchers identified brain networks involved in the placebo response, discovering that people whose symptoms improve in response to placebos—who feel better based on the mere expectation of relief—have more connections between certain brain regions than do people with muted placebo responses. The study essentially shows that there is a biological basis for the placebo response; it is real, and it also seems to be getting more powerful.

There’s nothing bad about experiencing the placebo response—if eating ginger eases your headache, and you don’t know whether the ginger or your expectations are to thank, who cares? Your headache is gone, so you’ll be taking ginger next time, too. But the existence of the placebo response does make it difficult to discern what’s actually easing your pain.

Since it’s so easy to believe health claims when we shouldn’t, science is an essential tool.

Studies are designed to bore through this clutter and illuminate how things really affect us. The best-designed studies are known as double-blind, randomized, placebo-controlled clinical trials (RCTs for short), and they work like this. Let’s say you want to know whether green tea improves depression. If you just give people green tea and then ask them if it’s helping, a lot of your subjects will probably say yes, but you won’t know whether the tea itself is helping, their depression eased on its own, or the placebo response is responsible.