Most over the counter pain relief creams, rubs and products contain chemical ingredients, synthetics or glycerin. One common ingredient, Methyl Salicylate, appears in most topical pain relief products. Methyl Salicylate (also known as wintergreen, salicylic acid, and methyl ester) is a wintergreen scented chemical similar to aspirin.
Other uses for methyl salicylate include: as a transfer agent for producing manual copies of images on a surface; in place of sulfur mustard when performing research and tests, (thanks to its similar physical & chemical properties) and as a biochemical insect & animal repellent.
Warnings associated with Methyl Salicylate include using with caution if you have nasal polyps, asthma, or sensitivities to aspirin; and that applying after strenuous exercise, during hot and humid weather, or using a heating pad in conjuction with products containing this ingredient can increase systemic absortion and the risk level.

Relief Response® and Pro Sports Response® do not contain methyl salicylate, only naturally derived essential oils. Creams contain a crystalline form of methyl salicylate that can actually burn your skin because of the high concentration. The oils in Response penetrate the skin and find the source of pain. .

Links to information about Methyl Salicylate:

MSNBC - Sports cream warnings urged after teen's death
The Washington Post - Bengay Death Hilights OTC Dangers
Avantor- Methyl Salicylate
Information About Side Effects and Warnings
National Institute of Health (U.S.)
Wikipedia - Methyl Salicylate

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