Adjuvants are immunological agents added to vaccines to modify the immune response. They work by broadening vaccine protection through extending the presence of antigens in the blood, improving immune response by helping absorb antigens to antigen presenting cells, and supporting the production of cytokines to activate lymphocytes and macrophages. Adjuvants are classified as mineral salt, oil, saponin, lipopolysaccharide, CpG, bacteria-derived, or emulsions.