Hank: A lot of us have been there, especially biosex females. You’re uncomfortable, and you’re going to the bathroom every few minutes. When you do, it’s almost unbearably painful.

You think you probably have a urinary tract infection—a UTI—and the first thing you might reach for before calling your doctor is a bottle of cranberry juice or cranberry pills. You’ll often hear cranberry juice touted as a great way to prevent UTIs, because it makes urine acidic, or because something in the cranberries keeps bacteria from sticking to the walls of the bladder, or... something... what... something? Well, turns out: they don’t.

UTIs are incredibly common: in the US alone, they send 8 million people to the doctor every year. They happen when bacteria, usually E. coli, find their way into the urethra, the tube that empties urine from your bladder. The bacteria can then infect the bladder, and in severe cases they can infect the kidneys, too.

And the symptoms aren’t fun: they include feeling like you need to pee all the time and pain when you do. Females are much more likely to get UTIs, because they have a shorter urethra, which means bacteria don’t have to travel very far to get to the bladder. But UTIs are also common in surgery patients or people who need catheters.

Most UTIs respond well to antibiotics—for now. In a 2012 study, researchers examined data from over 12 million E. coli samples from patients who had UTIs in the U. S. between 2000 and 2010.

They found that rates of drug resistance to the commonly prescribed antibiotic ciprofloxacin jumped from 3 percent to just over 17 percent in 10 years. And the rates of resistance to other drugs climbed, too. So these infections are still treatable, but doctors are starting to need stronger antibiotics to do it.

And since these infections are so common, and they can become very serious if they spread to the kidneys, researchers and doctors are always looking into ways to prevent them. Some prevention techniques are hygienic: for females, for example, wiping front-to-back after going to the bathroom can keep bacteria from getting into the urethra. And urinating right after sex can help flush out any bacteria that might’ve found their way in there.

But for decades, mothers and even doctors have suggested drinking unsweetened cranberry juice or to take cranberry pills to prevent UTIs. And there’s plenty of historical context for that advice: Doctors used to think that cranberries made urine more acidic, which would make the bladder and urethra an inhospitable place for bacteria. But more research showed that urine didn’t stay very acidic for long, and the amount of juice you would need to drink is probably more than any mortal could handle.

Later research turned to a specific type of antioxidant in cranberries called A-type proanthocyanidins, which were shown to prevent E. coli from adhering to the wall of the urethra and bladder. But these studies were conducted in cultured cells grown in petri dishes, and those kinds of results don’t always apply to real-world situations. So researchers have conducted quite a few human studies that compared the effects of cranberry juice, pills, and tablets to alternatives like placebos, drinking water, and antibiotics and probiotics to prevent urinary tract infections.

And they’ve found that cranberry does not out-perform any of the other treatments in controlled settings. In 2012, researchers compiled data from 24 studies and a total of more than 4,000 participants to see if they could parse out any benefit from cranberry. But no matter how you slice it, cranberries just don’t seem to stop people from getting UTIs.

In their analysis, the researchers suggested that part of the problem is that cranberry juice and pills simply don’t deliver enough of those proanthocyanidins to prevent bacteria from setting up shop in the bladder. But even though these studies have found that cranberry doesn’t do much for UTIs, you’ll still hear people claim that it helps them get fewer UTIs. You might also hear them say that it relieves their symptoms, even though cranberries were only ever thought to prevent UTIs, not cure them.

That’s probably just because of the placebo effect, though. A placebo is especially powerful if you’ve been told by a physician or another medical professional that it will work. And for a long time, doctors did recommend cranberry to prevent UTIs.

You might’ve also heard about it in the media and pop culture. So the power of suggestion is strong here, and might explain why reaching for that juice makes you feel better. Plus, sometimes infections just go away on their own.

Antibiotics work by preventing new bacterial growth as your immune system works to clear the infection, and sometimes the body can do that without the help of antibiotics. After all, before penicillin was invented people still got UTIs, and it wasn’t always a death sentence. So what seems to be cranberry juice at work is probably just your body clearing the infection.

If you actually want to keep yourself from getting a UTI, probably the best you can do is adopt those hygiene practices I mentioned earlier — if you’re female, wipe from front to back and pee right after sex. Wearing breathable, cotton underwear helps too, and you should also try to avoid holding in your urine. Some kinds of birth control, like spermicides and diaphragms, can make it easier to get a UTI, so if UTIs keep coming back, you might want to consider switching birth control methods. And for the love of god, if it burns when you pee, go see a doctor.

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