Cinnamon flavoring agents are known to act on the mucosa as irritants or sensitizers. The objective of this study was to report on clinical and histologic features important in the diagnosis of cinnamon-induced contact stomatitis. We examined 37 past cases of contact stomatitis and identified clinical signs and symptoms and possible causes. The most common cause in the 37 cases was toothpaste; other causes were chewing gum and foods. Although various clinical findings were observed, some characteristics were evident. The most commonly affected site was the gingiva, which showed diffuse or generalized erythema and epithelial sloughing. It is important to identify the causative agents of such a disorder by understanding characteristic signs and symptoms and conducting an appropriate inquiry.