evidence: Some parents are concerned about ingredients contained in vaccines, specifically aluminium, mercury, gelatine and antibiotics. However, parents can be reassured that ingredients in vaccines are minuscule and necessary. [...] The most common preservative used was thiomersal, a mercury-containing compound. As more vaccines were given, children received greater quantities of thiomersal. By the late 1990s, the American Academy of Paediatrics and the Public Health Service requested that mercury be removed from vaccines to make ‘safe vaccines safer’. No evidence existed to suggest that thiomersal was causing harm, but they wanted to be cautious. Unfortunately, their caution worried parents who wondered whether mercury in vaccines was causing subtle signs of mercury poisoning or autism. Addressing these concerns, scientists performed several studies, all of which showed that thiomersal at the level contained in vaccines hadn’t caused harm. Further, because mercury is a naturally occurring element found in the earth’s crust, air, soil and water, we are all exposed to it. In fact, infants who are exclusively breast fed ingest more than twice the quantity of mercury than was contained in vaccines. [...] In addition to gelatin, other ingredients in vaccines such as egg proteins and antibiotics might cause an allergic reaction. Because the influenza and yellow fever vaccines are grown in eggs, the final products contain sufficient quantities of egg proteins to cause an allergic reaction, albeit rarely, in people allergic to eggs.