An adjuvant is “a substance which accelerates, prolongs and enhances the quality of a specific immune [antibody] response when incorporated into a vaccine formulation.”  Since the turn of the 20^th century, when they were first used in the production of diphtheria anti-toxin, many chemicals have been investigated and introduced as adjuvants in vaccines, and more are being developed.  What are the reasons for adjuvant use, and what side effects might they have?