What is thimerosal?

Thimerosal is a mercury-based preservative that has been used for decades in the United States in multi-dose vials (vials containing more than one dose) of some vaccines to prevent the growth of germs, bacteria and fungi, that can contaminate them.

Thimerosal contains approximately 49% ethylmercury. There is no convincing evidence of harm caused by the low doses of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site.

Last Reviewed: 10/25/2010

• Is thimerosal still being used in vaccines?
• Is thimerosal safe when used as a preservative in vaccines?

• Vaccines
  • Health Issues & Vaccines
    • Thimerosal