Menthol and methyl salicylic acid are the active ingredients in over-the-counter creams for pain relief. Both are natural compounds from plants and can be synthesized in the laboratory. Though used for similar symptoms of joint and muscle pain, the two chemicals differ in chemical composition and mechanism of action.
Plant Sources
Menthol gives the perennial plants in the mint family their characteristic scent. Methyl salicylic acid can be found in wintergreen or the bark of the sweet birch. Native American herbalists used the leaves of the flowering shrub wintergreen to reduce pain or fever. In small doses, food-grade preparations of mint and wintergreen add flavoring to foods or can be used to make herbal teas.
Characteristics
Methyl salicylic acid, also known as methyl salicylate, exists as an oil at room temperature and may be colorless, reddish or yellowish. According to the Annals of Clinical Microbiology and Antimicrobials, menthol exists as a white crystalline that remains solid at room temperature and melts at slightly above room temperature.
Mechanisms of Action
Methyl salicylate, related to both aspirin and the acne medication salicylic acid, blocks chemicals in the body that cause pain. Menthol creates a cold sensation to provide distraction from the primary pain. A mouse study published in Molecular Pain in 2010, shows menthol activates the sensory neurons responsible for detecting cold stimuli.
Menthol and Antibacterial Activity
In addition to providing pain relief, the naturally occurring essential oil of menthol from plants provides antimicrobial activity. According to a study published in Annals of Clinical Microbiology and Antimicrobials in 2009, menthol essential oil inhibited bacterial growth of five strains of gram-positive bacteria and offered anti-fungal activity against Candida albicans.
Methyl Salicylate and Aspirin Toxicity
Methyl salicylate may cause aspirin toxicity, especially in children, due to the similarity of the chemicals. According to a study published in Journal of Toxicology in 2003, wintergreen oil absorbed quickly by mouth increased aspirin-equivalent salicyclic acid levels in the blood. The researchers noted methyl salicylate in topical analgesic cream showed delayed absorption under conditions of accidental ingestion and produced a lower aspirin-equivalent dose.
Warning
According to MedlinePlus, possible symptoms of overdose from topical analgesic creams containing either menthol or methyl salicylate include changes in breathing, dizziness, loss of vision, ringing in the ears, and nausea and vomiting. Menthol and methyl salicylic acid may produce allergic reactions in sensitive individuals. Seek medical attention for symptoms including rash and severe itching of the skin, any swelling of the throat or mouth or difficulty breathing. Contact a poison control center or seek medical attention if menthol or methyl salicylic acid topical analgesic creams are accidentally taken by mouth.
References
- "Annals of Clinical Microbiology and Antimicrobials;" Isolation and identification of antimicrobial compound from Mentha; Firas A Al-Bayati; June 12, 2009
- Environmental Protection Agency: Methyl Salicylate Biopesticide Registration
- "Molecular Pain"; The Roles of iPLA2, TRPM8 and TRPA1 in Chemically Induced Cold Hypersensitivity; Clive Gentry, Natalie Stoakley, David A. Andersson and Stuart Bevan; January 2010
- "Journal of Toxicology"; Plasma Salicylate from Methyl Salicylate Cream compared to Oil of Wintergreen; WR Wolowich et al; 2003
- MedlinePlus: Sports Cream Overdose
