And in the case of hair growth, a 2013 animal study4 looks promising. Originally, the researchers wanted to measure the GI immune-related benefits of L. reuteri, “but they noticed that the mice who got the reuteri developed all kinds of unexpected effects,” Davis recounts. “Their skin healed faster. They had more lustrous, moist hair.” Not to mention, the mice had thicker skin and stronger, more lush hair after eating the probiotic-laced yogurt and after drinking L. reuteri-infused water—meaning, there was something about this specific probiotic strain that leads to what researchers call a “glow of health.”