02/07/2014 02:25 pm ET Updated Feb 10, 2014

How Dangerous Is That Sketchy Subway Bread Chemical, And Who Else Uses It?

An employee prepares a customer's sandwich order at the food counter of a Subway fast food restaurant in Moscow, Russia, on S
An employee prepares a customer's sandwich order at the food counter of a Subway fast food restaurant in Moscow, Russia, on Sunday, April 7, 2013. McDonald's, which virtually created the market for burgers and fries in the country and convinced Russians it's OK to eat with their hands, must fend off a growing challenge from rivals Burger King Worldwide Inc., Subway Restaurants, Yum! Brands Inc. and Wendy's Co. Photographer: Andrey Rudakov/Bloomberg via Getty Images

Subway announced Wednesday it will remove from its bread recipe a chemical that is also found in yoga mats and rubber-soled shoes. The change followed a petition by food blogger Vani Hari, who asked Subway to stop using azodicarbonamide and argued that the chemical poses a direct health risk. But how dangerous is this stuff really? And who else is using it?

Subway was specifically targeted due to its “healthy” image, but it is by no means the only restaurant to use the chemical. Multiple sources have pointed out that popular chain restaurants -- McDonald's, Burger King, Kentucky Fried Chicken, Starbucks, Arby’s and Dunkin’ Donuts, to name a few -- also use the substance as an ingredient. In fact, the Food and Drug Administration's guidelines on food and health safety for corporations permit the use of azodicarbonamide.

Hari's petition mentions that exposure to it could be linked to asthma, respiratory problems, cancer and skin irritation. But those of you who bought a $5 footlong Subway sandwich for lunch probably don’t need to worry.

According to a 1999 World Health Organization evaluation of studies on the effects of azodicarbonamide, there was a negligible impact from the chemical in animal test subjects, except in massive doses. All information regarding human testing was inconclusive. (Hari also cited this WHO report in her Subway petition.)

Azodicarbonomide was administered in controlled doses by “inhalation and oral routes” in rats that were tested in one of the studies examined by the WHO. However, the substance remained “unabsorbed from the gastrointestinal tract” and passed through the rodents with no noticeable effect. Elimination of the azodicarbonamide was found to be rapid (predominantly through the evacuation of urine), and the study authors concluded that the chemical has little systemic retention.

Perhaps some of the most damning evidence of the chemical's side effects have to do with stories of dogs that met their end in lab experiments with the chemical. This information comes from a one-year study the WHO found in which rats and dogs were exposed to diets containing various levels of biurea, a chemical created from azodicarbonaminde. One rat in the high-exposure group died, and most of the dogs in both groups died.

The WHO report also cites studies that examined bread baked with azodicarbonamide. Subject animals died but were of varying backgrounds, so no useful statistics could be gleaned. As a result, the link between the chemical and these deaths is circumstantial.

At the end of the day, it's not advisable to scent one's room with an azodicarbonamide air freshener (were one to exist), but it doesn't seem likely that Subway has been poisoning customers all these years, so rest easy.

CORRECTION: This article originally stated incorrectly that the petition cited death in dogs during lab tests. It has since been corrected.