My first meal at Saint Ann, the subject of this week's print review, was marred by sloppy service, gummy pasta and -- most memorably -- a hair in my chicken.

As human products go, hair is relatively innocuous. There are far worse bodily secretions in food that no eater can see: The contamination that should really cause diners concern is the fecal matter transferred from a prep cook's unwashed hands or the spit that dripped from a server's mouth.

But a strand of dead hair is the ogre of every restaurant horror story. In amateur reviews on Yelp, the appearance of a stray hair (short and curly, if the writer's feeling especially feisty) almost always marks the climax of a pan. The soup's cold, the steak's burnt, and then -- and here, reviewers always use ellipsis, the literate equivalent of ominous organ music - there's a HAIR IN THE MASHED POTATOES. Enough said. No other restaurant sin can match it.

Are customers' hair hang-ups overblown? Balding men and alopecia sufferers excepted, all people have about 100,000 strands of hair on their heads. We're bound to lose one or two. And sometimes those hairs land in the pad Thai.

So I asked Dr. Valerie Curtis of the London School of Hygiene and Tropical Medicine why most diners can't stomach a meal after they've found a hair in it. Curtis is an expert on the topic of disgust: She studies the what and why of squeamishness, a research field she entered after coordinating a major study of diarrhea.

Curtis believes there are evolutionary underpinnings for disgust. While other scholars have argued disgust is a cultural construct, Curtis has discovered a few items provoke "eww"s from people of all backgrounds. Humans everywhere agree bodily secretions; certain bodies and body parts (corpses and toenail clipping); decaying food; a select group of animals (lice and maggots); and sick people are disgusting. That involuntary response is protective, since it prevents people from acquiring infectious diseases by handling vomit and eating rotten meat.

Same goes for hair, Curtis says.

"It's better to overdetect pathogen risk and miss a meal than possibly contract a life-threatening illness," Curtis e-mails. "Anything that cues possible contamination from others' body products is therefore best avoided. If there's a hair in your food -- what else has got in there too?"

And while the hair cooked into my chicken at Saint Ann didn't pose any real danger, Curtis says eaters are right to worry about raw hair.

"Human hairs can actually transmit ringworm -- a fungal infection," she adds.

So Yelpers, keep complaining about your hairy food: It's what the doctor ordered.