Menthol, methyl salicylate, and camphor are all considered counterirritants because they create a heating or cooling sensation that provides relief of acute or chronic pain. The counterirritant class of topical analgesics produces pain relief by activating and then desensitizing epidermal nociceptors, thereby decreasing the perception of pain1.
Ingredients such as menthol, methyl salicylate and camphor are called counter-irritants because they produce irritation in one part of the body to help relieve irritation in another. Upon contact, they create a warming or cooling sensation to dilate blood vessels, re-oxygenate the tissues and relax muscles to ultimately stop the pain messages that are being sent to the brain via nerves in the body2.
Menthol, methyl salicylate and camphor occur in numerous over-the-counter products. For all three, low dose dermal application for an extended time does not result in high concentrations in the blood3.
Menthol is an alcohol that is found in mint oils, and similar to peppermint, has a refreshing odour and cooling properties. Medicinally, it is often used to topically to treat sore muscles as well as relieve pain, itching, and nasal congestion4.
Menthol is found in many topical pain relief medications due to its counter-irritant and local anaesthetic properties2. The mechanism by which menthol is able to impart a cooling sensation when applied topically to the skin is well understood2. Menthol in over-the-counter concentrations has an excellent safety profile2.
Methyl salicylate is produced by many species of plants, particularly wintergreens. When used medicinally, it creates a mild local reaction that provides relief at the area of pain. It may cause analgesic (pain relief) and anti-inflammatory effects by inducing vasodilation thereby increasing blood flow and temperature to the localized area of tissue5. This often is experienced as a feeling of warmth.
Camphor is a compound obtained from the wood and bark of the camphor tree found in Taiwan and Southeast Asia6. It is used to treat pain because of its soothing properties. Camphor has a long history of medicinal use7. It has been found to increase the perceived intensity of sensations on the skin produced during heating and cooling, thereby heightening the sensation of temperature7.
[footnote num="1"]Barkin, R. L. (2013). The pharmacology of topical analgesics. Postgraduate Medicine, 125 (4 supp 1), p. 7-18. [/footnote]
[footnote num="2"]Patel, T., Ishiuji, Y., &Yosipovitch, G. (2007). Menthol: A refreshing look at this ancient compound. Journal of the American Academy of Dermatology, 57, p. 873-878. [/footnote] [footnote num="3"]Martin, D., Valdez, J., Boren, J., &Mayersohn, M. (2004). Dermal absorption of camphor, menthol and methyl salicylate in humans. Journal of Clinical Pharmacology, 44, p. 1151-1157. DOI: 10.1177/0091270004268409.[/footnote] [footnote num="4"]http://www.medilexicon.com/medicaldictionary.php?t=54219[/footnote] [footnote num="5"]Yoshinobu, H., Kiuchi, T., &Furata, K. (2010). Efficacy and safety profile of a topical methyl salicylate and menthol patch in adult patients with mild to moderate muscle strain: A randomized, double-blind, parallel-group, placebo-controlled, multicenter study. Journal of Clinical Therapeutics, 32(1), p. 34-43.[/footnote] [footnote num="6"]http://www.medilexicon.com/medicaldictionary.php?t=13542[/footnote] [footnote num="7"]Green, B. G. (1990). Sensory characteristics of camphor. The Journal of Investigative Dermatology, 94(5), p. 662-666. [/footnote]