Balsam of Peru, also known as myroxylon, is a sticky sap that smells like vanilla and cinnamon. It's used as an ingredient in soaps, perfumes and shampoos both for its smell and for its quality as a fixative, which helps slow down evaporation. It's also added to certain medications and food, showing up in everything from calamine lotion to cough medicine and cola.
Cinnamein, a well-documented potential allergen, makes up between 60 and 70 percent of balsam of Peru, while the other 30 to 40 percent is made of unknown resins, any of which can provoke an allergic reaction. It's one of the most common causes of contact dermatitis, and about half of people who have a fragrance allergy have a reaction to balsam of Peru. The most common symptom is hand eczema in the case of skin contact, and when it's consumed, rashes may form around the mouth [source: Duffill].