Azodicarbonamide (Yoga Mat Chemical)

Azodicarbonamide is used as a flour bleaching agent and dough conditioner in American bread — and also as a foaming agent in yoga mats and shoe soles. Subway famously removed it in 2014 after food blogger Vani Hari's petition went viral (calling it "the yoga mat chemical" was genius marketing). It's banned in the EU (where exposure during manufacturing can cause asthma) and Australia. The WHO says it's safe in bread at approved levels, but the optics of sharing an ingredient with exercise equipment were devastating. Most major US bread companies have since removed it voluntarily, but it's still FDA-approved.