Menthol is an organic compound , specifically a monoterpenoid , that occurs naturally in the oils of several plants in the mint family, such as corn mint and peppermint.
It is a white or clear waxy crystalline substance that is solid at room temperature and melts slightly above. For many people, menthol produces a cooling sensation when inhaled, eaten, or applied to the skin, and mint plants have been used for centuries for topical pain relief and as a food flavoring.
Menthol has local anesthetic and counterirritant qualities, and it is widely used to relieve minor throat irritation. Menthol has been demonstrated to cause a subjective nasal decongestant effect without any objective decongestant action, and administration of menthol via a nasal inhaler in humans has also been shown to cause nasal congestion.
Natural menthol exists as one pure stereoisomer , nearly always the 1 R ,2 S ,5 R form bottom left corner of the diagram below. The eight possible stereoisomers are:.
In the natural compound, the isopropyl group is in the trans orientation to both the methyl and hydroxyl groups. Thus, it can be drawn in any of the ways shown:.
