The U.S. Food and Drug Administration (FDA) is alerting the public that certain over-the-counter (OTC) products that are applied to the skin for the relief of mild muscle and joint pain have been reported to cause rare cases of serious skin injuries, ranging from first- to third-degree chemical burns, where the products were applied. These OTC topical muscle and joint pain relievers are available as single- or combination-ingredient products that contain menthol, methyl salicylate, or capsaicin. The various formulations include creams, lotions, ointments, and patches.
When applied to the skin, the products produce a local sensation of warmth or coolness; they should not cause pain or skin damage. However, there have been rare cases of serious burns following their use (seeData Summary below). Some of the burns had serious complications requiring hospitalization. In many cases, the burns occurred after only one application of the OTC topical muscle and joint pain reliever, with severe burning or blistering occurring within 24 hours of the first application. Based on the reported cases, the majority of second- and third-degree burns occurred with the use of products containing menthol as the single active ingredient, and products containing both menthol and methyl salicylate, in concentrations greater than 3% menthol and 10% methyl salicylate. Few cases reported using a capsaicin-containing product.
http://www.fda.gov/Drugs/DrugSafety/ucm318858.htm
