It has been used as a preservative in vaccines, immunoglobulin preparations, skin test antigens, antivenins, ophthalmic and nasal products, and tattoo inks.

Morris Kharasch, a chemist then at the University of Maryland filed a patent application for thiomersal in 1927;[16] Eli Lilly later marketed the compound under the trade name Merthiolate.

[17] In vitro tests conducted by Lilly investigators H. M. Powell and W. A. Jamieson found that it was forty to fifty times as effective as phenol against Staphylococcus aureus.

[19] In the United States, the European Union, and a few other affluent countries, thiomersal is no longer used as a preservative in routine childhood vaccination schedules.

[21] The United Nations Environment Program backed away from an earlier proposal of putting thiomersal on the list of banned vaccine compounds as part of its campaign to reduce mercury exposure.

Later it was reported that ethylmercury is eliminated from the body and the brain significantly faster than methylmercury, so the late-1990s risk assessments turned out to be overly conservative.

A 2007 study in Norway found that 1.9% of adults had a positive patch test reaction to thiomersal;[29] a higher prevalence of contact allergy (up to 6.6%) was observed in German populations.

This difference in the sensitization rates can be explained by changing exposure patterns: The adolescents received six thiomersal-preserved vaccines during their life course, with the last immunization taking place 2–3 years before the study.

[33] The Center for Biologics Evaluation and Research (CBER) at the FDA initiated a formal risk assessment of thiomersal in vaccines beginning in 1998.

[17] The scientific consensus is that no evidence supports these claims, while the rate of autism continued to climb in children who did not take the thiomersal-preserved childhood vaccines.

[9][38][39][7] Scientific and medical bodies such as the Institute of Medicine[7] and World Health Organization,[40][41] as well as governmental agencies such as the Food and Drug Administration[18] and the CDC[42] reject any role for thiomersal in autism or other neurodevelopmental disorders.

[43] Unconvinced parents attempted to treat their autistic children with unproven and possibly dangerous treatments, and refused to vaccinate them due to fears about thiomersal toxicity.

[45] Thousands of lawsuits have been filed in U.S. federal court to seek damages from allegedly toxic vaccines, including those purportedly caused by thiomersal.