Thimerosal

Thimerosal (sometimes spelled as thimerosol) (trade name: Merthiolate) is a commonly-used preservative, used primarily in children's vaccinations. Its chemical formula is C₉ H₉HgNaO₂S. It has been in use since the 1930s.

Despite a lack of empiric evidence, some have hypothesized a relationship between thimerosal exposure from childhood vaccines and autism. In a 2001 report, the Institute of Medicine concluded "that the evidence is inadequate to either accept or reject a causal relationship between thimerosal exposure from childhood vaccines and the neurodevelopmental disorders." The National Institute of Allergy and Infectious Diseases concluded that the "only known side-effects of receiving low doses of thimerosal in vaccines have been minor reactions such as redness and swelling at the injection site." Concerns about mercury toxicity have nevertheless led to the production of many thimerosal-free vaccines.