The menthol molecule is comprised of four isomers: menthol, isomenthol, neo-isomenthol and neo-menthol, These are complicated by the fact that each isomer has two chiral antipodes having positive and negative rotation. What is commonly called menthol in nature and in commerce is the l-menthol chiral isomer.
L-menthol can redescribed as unique in the aromachemical world for the cooling sensation it imparts to the skin and mucous membranes. This cooling effect is far greater than the cooling that occurs when a solvent, such as ethanol or hexane, is placed on the skin. Although other materials are known to display such a cooling effect, almost all of them are derivatives of l-menthol.
Organoleptically, l-menthol displays a minty, light, refreshing odor that at most practical concentrations is complicated by an intense numbing-cooling sensation. At very low concentrations, menthol displays a slight warming sensation, along with the refreshing mint odor. At moderateconcentrations, the cooling effect develops. As concentration increases, the cooling effect becomes overwhelming and desensitizing, producing a cooling-anesthetic reaction.
