Aromatic substance obtained from the wood of a tree common to Southeast Asia, Cinnamomum camphora or manufactured synthetically. When applied to the skin, camphor produces a cooling effect, which can cause skin sensitivity with repeated use. Inhaling camphor at concentrations of 2 ppm (parts per million) or more may cause sensitivity of the mucous membranes. Camphor can also cause skin and eye sensitivity on contact.
References for this information:
British Journal of Dermatology, November 2000, issue 5, pages 923-929