Although cinnamon is known to cause dermatitis in bakers and confectioners, it has only rarely been reported as causing trouble in food or cosmetics. A newly-formulated 'spicy' toothpaste containing cinnamon as a flavouring agent was the cause of oral symptoms in eight patients referred to clinics in Buckinghamshire and in Malmö and in a further eight patients discovered subsequently. Similar symptoms and patch test results were observed independently at both centres. Positive reactions were obtained with 1% cinnamic aldehyde in 15 out of 16 patients tested. Only one patient reacted to a standard sample of balsam of Peru (25% in petrolatum).