Alhydrogel is an aluminium hydroxide (referred to as alum) wet gel suspension. Alum improves attraction and uptake of antigen by antigen presenting cells (APCs). Recently, it has been suggested that the antigens adsorbed on the aluminum salts are presented in a particulate form, making them more efficiently internalized by APCs. Moreover, alum activates the NLRP3 inflammasome complex implicated in the induction of several pro-inflammatory cytokines including IL-1β and IL-18. Alum increases Th2 antibodies but does not promote significant Th1 cellular response.2% Aluminum hydroxide was elected as the International Standard Preparation for aluminium hydroxide gels. 2% Aluminum hydroxide is present in multiple commercial vaccine formulations.