glow of health

Susan Erdman, a microbiologist at M.I.T., calls it the “glow of health.” The microbes you harbor, she argues, can make your skin smooth and your hair shiny; they may even put a spring in your step. She stumbled on the possibility some years ago when, after feeding mice a probiotic microbe originally isolated from human breast milk, a technician in her lab noticed that the animals grew unusually lustrous fur. Further observation of males revealed thick skin bristling with active follicles, elevated testosterone levels and oversize testicles, which the animals liked showing off.

Some of the mice in her studies were eating a high-fat, high-sugar diet — junk-foody fare that’s known to shift the microbiome into an unhealthy state. Not surprisingly perhaps, mothers that didn’t imbibe the probiotics were less caring and tended to neglect their pups. But mothers that had high oxytocin thanks to the probiotic were nurturing and reared their pups more successfully.

Then there’s the mystery of body odor. Back in the days before deodorant, one’s stench probably conveyed important information. And it still apparently does. In one classic Swiss study, women were asked to sniff T-shirts previously worn by men and rate their pleasantness. The women tended to prefer shirts from men whose immune-system genes were most different from their own, and with whom they’d most likely produce the fittest offspring. Their noses led them, unawares, to the best genetic matches.