Vaccine adjuvants are needed to improve the adaptive immune responses to antigens. Adjuvants show their effects through different mechanisms. Some adjuvants work as delivery systems that provide stimulation of the immune system. Immunologic adjuvants are added to vaccines for the stimulation of the response of immune system to the target antigen, but directly do not provide immunity. Adjuvants may act in various ways to present an antigen in the immune system. Adjuvants may also act as the irritant to engage and amplify the body immune response.