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Methyl salicylate is an organic ester or oil naturally produced by several plant species with a strong mint odor used as a pharmaceutical, food, and cosmetics additive. The aromatic oil is produced by plants as a part of their defense mechanism against herbivorous insects and pathogens. Its industrial applications include food flavoring, as a cosmetic fragrance additive, and as a rubefacient in pharmaceutical preparations such as liniments and creams. Although considered safe for human use, some fatal cases of over dosage have been recorded.
Wintergreen is the more commonly used generic name for methyl salicylate and is derived from a group of plants that contain strong concentrations of the oil. These wintergreens, which include shrub families such as the Eastern Teaberry, are among several plant groups which produce methyl salicylate. Other plant sources of the oil include the Pyrolaceae, Betulaceae, and Spiraea genuses. All of these plants are believed to produce the strong odored oil as an attractant to beneficial insects which feed on herbivorous pest insects. Methyl salicylate production in these plant species may also serve as a pherenome warning to others of the presence of certain pathogens.
In the past, commercial production of the substance was achieved by distilling the ester from plants such as Sweet Birch and Eastern Teaberry. Modern synthetic production methods involve an esterification process of salicylic acid and methanol. Wintergreen is used as an additive and laboratory agent in a diverse selection of applications based on its aromatic odor and strong rubefacient or blood vessel dilating qualities. As a flavorant, wintergreen is added to toothpaste, candy, and soft drinks as an alternative to other mint flavors such as spearmint and peppermint. The aromatic odor of the oil is also useful as a fragrance in many cosmetic preparations.
The oil is also used frequently as a laboratory agent to clear tissue samples of color for microscopy and immunohistochemistry work. Once tissue samples have been dehydrated in alcohol, methyl salicylate removes all vestiges of light blocking pigments. Wintergreen is also used as a simulation agent for lethal chemical warfare chemicals such as sulfur mustard. Entomologists studying insects such as orchid bees utilize wintergreen as bait to collect the insects which use the oil to produce pheremones. Methyl salicylate is also an antifreeze agent for chemical transport in cold climates.
It is, however, the lotions and creams for addressing muscle and joint pain which are the best known application of wintergreen. The oil causes localized capillary dilation, thereby resulting in an increase in temperature in the area of application, which in turn relieves muscular pain. Although the use of wintergreen in all these products is deemed to be safe, there have been cases of accidental overdose, however, several of which have been fatal. Methyl salicylate in a pure form is toxic, and excessive use of any product containing therapeutic levels of the oil may lead to poisoning. As is the case with all products containing wintergreen, they should be used only in strict accordance with the manufacturer's instructions.