Pharmacies are full of things that won’t necessarily heal us — vitamin C, homeopathic drops, probiotics — but we shrug and buy them anyway because, hey, they can’t hurt. But now we have some concrete evidence that probiotics can hurt, if they aren’t exactly the right ones for the health condition you’re trying to treat.

Even at our cleanest, we are covered in germs and we are full of germs. It's ok! That's totally normal. These microorganisms are essential to our health. You probably don't need to mess with them, but if you'd like to try, the terms to know are prebiotics and probiotics.