If you’ve ever been pregnant (or had chemotherapy: The two have similar side effects), you might know what it’s like to have a smell that’s your own particular bête noire. It might be eggs, or garlic, or coffee, or the reek of your spouse’s morning breath. For me, it was the smell of Subway.

There is a Subway franchise in the hospital where I had my child, located right at the top of an escalator. As the escalator would rise to the level of the Subway, the smell would start right about the fourth or fifth stair: sweaty low-quality meat, limp vegetables, layers of old vinegar, and something else. A something that I couldn’t define or pin down. Burning plastic? Melting rubber?

Whatever it was, it would leave me gasping with nausea on every visit, enough that I talked to other people about the Subway stink and found I wasn’t alone. Not everyone perceives the horrible smell of Subway, distinct and distinctly more awful than that of other fast-food chains or delis, even crappy ones, but those who do find the smell nigh on unbearable. The question “What makes that awful reek?” has been the topic of well-attended discussions on Chowhound and MetaFilter, but to my knowledge, no one has ever produced a satisfactory answer.

Like many of the respondents to those threads, I think that the smell has something to do with the bread-baking. The smell seems to almost push itself out, wafting through the front doors each time they’re opened, in a way that seems bread-baking-like to me. And Subway is constantly baking, with bread in frozen sticks thawed and cooked many times daily.

But despite polling numerous food scientists, I still haven’t found an answer to the smell conundrum. Even a query to the usually infallible Monell Chemical Senses Center came to naught. Several scientists said they had never noticed an aroma, or couldn’t see anything in the (creepily-full-of-multisyllabic-items) list of ingredients for Subway’s breads that might account for off odors.

The only scientist even willing to speculate with me was Barry Swanson, a retired professor of food science who used to work for Washington State University. He thinks that the smell might be the odor of fatty acids released from the vegetable oils in the bread as it bakes.

“Fatty acids are volatile and may present many aromas depending on composition,” Dr. Swanson said via email. “Short chain fatty acids result in undesirable aromas resembling everything from butter to smelly feet.”

“Smelly feet” doesn’t perfectly describe the odor either (there is a plasticlike quality, I just know it), but it’s as close to an answer as I’ve been able to get. Any food scientists out there want to theorize?

Image source: Flickr member Vincent Desjardins under Creative Commons