evidence: All of the ingredients in vaccines are safe in the amounts used. You may have heard or read that some vaccine ingredients are harmful, but this is true only at much higher amounts than those present in vaccines. Any substance, even water, can be harmful at a high dose. [...] Vaccine ingredients have been carefully studied for a long time and are safe in the small amounts used. The ingredients in vaccines have not been proven to cause harm (disease or illness) in the small amounts used in vaccines, with the exception of allergic reactions in people with hypersensitivity to a specific ingredient. Before administering a vaccine, your health care provider will: