Intraoral allergic contact dermatitis (ACD) is an uncommonly reported entity. The most commonly implicated allergens are metals that are incorporated into dental appliances. Intraoral ACD to nonmetal allergens is even less frequently described. Cinnamic aldehyde is widely used as a flavoring agent in foods and dentifrices. However, intraoral ACD to cinnamon flavoring agents has only been sporadically reported. In these cases, a variety of sources have been implicated, including candy, chewing gum, mouthwash, lip sunscreen, cinnamon toast, volatile oils, and toothpaste. The clinical presentation of intraoral ACD reactions varies greatly, and as a result, clinicians often do not recognize the diagnosis. Furthermore, because patients are typically unable to provide a list of putative allergens, a high degree of clinical suspicion is required to make the correct diagnosis. We describe several patients with intraoral ACD caused by cinnamon and review the literature associated with this condition.