evidence: Why is aluminum in some vaccines? Aluminum salts are incorporated into some vaccine formulations as an adjuvant. An adjuvant is a substance added to some vaccines to enhance the immune response of vaccinated individuals. The aluminum salts in some FDA-approved vaccines are aluminum hydroxide, aluminum phosphate, alum (potassium aluminum sulfate), or mixed aluminum salts. For example: aluminum salts are used in DTaP vaccines, the pneumococcal conjugate vaccine, the HPV vaccine, and hepatitis B vaccines. Aluminum adjuvant containing vaccines have a demonstrated safety profile of over many decades of use and have only uncommonly been associated with severe local reactions. Of note, the most common source of exposure to aluminum is from eating food or drinking water.