evidence: For the most part, vaccines combine the following types of ingredients: Antigens to help your body build immunityStabilizers and other ingredients to help vaccines stay safe and effective for a long timeIngredients, like aluminum salt, to help your body respond to the vaccine But they also contain (or previously contained) some ingredients that worry parents. One of those ingredients was thimerosal, a preservative containing ethylmercury (a type of mercury cleared from the body more readily than methylmercury, the kind of mercury found in fish). Vaccine Schedule for Babies and Toddlers Why Are People Concerned About Mercury in Vaccines? Parents have had many fears about mercury in vaccines, from a concern that mercury exposure could lead to learning disabilities to immune system and organ damage, to nervous system problems. Learning disabilities Fears about mercury stemmed from research showing that exposure to high doses can cause learning disabilities and damage the brain. This is why mercury is often blamed by those who suggest a connection between vaccines and autism. However, older studies published a few years after thimerosal was removed from vaccines found the opposite to be true. [...] Pediatrics. 2003. Thimerosal-containing vaccines and autism: a review of recent epidemiologic studies. J Pediatr Pharmacol Ther. 2010. Science summary: CDC studies on thimerosal in vaccines. Centers for Disease Control and Prevention. n.d. Institute of Medicine (US) Immunization Safety Review Committee. Immunization Safety Review: Vaccines and Autism. 2004. World Health Organization. 2023.