MILFORD, CONN. — Subway began the process of removing azodicarbonamide, a dough conditioner, from its bread even before petitions asked them to stop using it, the restaurant chain said Feb. 7.

“We are already in the process of removing azodicarbonamide as part of our bread improvement efforts despite the fact that it’s a U.S.D.A.- and F.D.A.-approved ingredient,” Subway said. “The complete conversion to have this product out of the bread will be done soon.”

According to the Code of Federal Regulations in the United States, azodicarbonamide may be used as a dough conditioner in bread baking in a total amount not to exceed 45 parts per million by weight of the flour used.

Vani Hari, who created, on Feb. 4 started a petition asking Subway to remove the dough conditioner. The same day the Washington-based Center for Science in the Public Interest urged the Food and Drug Administration to bar the use of azodicarbonamide as a food additive or at least reduce the amount allowed for use.

According to the C.S.P.I., two chemicals form when bread with azodicarbonamide is baked. One, semicarbazide, causes cancers of the lung and blood vessels in mice. Another chemical, urethane, is a carcinogen.

Researchers at the Agricultural University of Hebei in China found azodicarbonamide partially degrades with the heat of processing to form trace amounts of semicarbazide, which shows carcinogenicity and also has been shown to cause tumors. The study appeared in the Sept. 14, 2011, issue of the Journal of Agricultural and Food Chemistry.

The World Health Organization, Geneva, issued a report on azodicarbonamide in 1999.

“Azodicarbonamide is of low acute toxicity, but repeated or prolonged contact may cause asthma and skin sensitization,” the report said.

Azodicarbonamide also is used in the production of plastic. According to the W.H.O. report, a number of reports have been published of individual workers, including those in plastic manufacturing plants, alleging asthma induced by exposure to azodicarbonamide.