Thimerosal is a mercury-containing preservative that has been used in some vaccines and other products since the 1930's. There is no evidence that the low concentrations of thimerosal in vaccines have caused any harm other than minor reactions like redness or swelling at the injection site. However, in July 1999 the U.S. Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated from vaccines as a precautionary measure. Today, all routinely recommended childhood vaccines manufactured for the U.S. market contain either no thimerosal or only trace amounts.