Aluminum salts are chemical compounds formed when the metal aluminum bonds with other elements, such as sulfates, chlorides, or hydroxides. These compounds are distinct from metallic aluminum, a soft, silvery-white element commonly used in manufacturing. Aluminum is the third most abundant element in the Earth’s crust, meaning its compounds are naturally pervasive. Understanding aluminum salts is relevant because they are intentionally incorporated into a wide range of consumer products and industrial processes, extending from personal hygiene items to the water and food we consume.
Chemical Identity and Common Forms
Aluminum salts are ionic compounds, meaning they consist of positively charged aluminum ions bonded to negatively charged ions. This structure allows them to dissolve in water and react readily. One of the most commercially significant forms is Aluminum Chlorohydrate (ACH), which is a group of water-soluble complexes. ACH is a partially neutralized form of aluminum chloride that functions effectively as an astringent.
Another common compound is Aluminum Sulfate, frequently referred to simply as Alum, an inorganic salt that readily dissociates in water. Alum is known for its ability to neutralize the charge of microscopic particles suspended in water, a process that is essential in industrial applications. Aluminum Hydroxide is a third form, characterized by its low solubility and ability to react with both acids and bases. This amphoteric nature makes Aluminum Hydroxide useful in environments with varying pH levels, such as the human digestive system or in vaccine formulations.
Widespread Use in Personal Care Products
The most recognized use of aluminum salts is their incorporation as the active ingredient in antiperspirant products. The primary compounds used are Aluminum Chlorohydrate (ACH) and complex salts like Aluminum Zirconium Tetrachlorohydrex Glycine. These salts function by physically limiting the flow of sweat to the skin’s surface.
The salts dissolve in the moisture of the underarm area, creating a highly concentrated solution that then interacts with the sweat ducts. This interaction is explained by the “Gel Plug Theory,” where the dissolved salts react with proteins and mucopolysaccharides found in sweat. The reaction forms an amorphous, occlusive gel mass that temporarily blocks the opening of the eccrine sweat duct.
This action is temporary, as normal skin cell turnover eventually causes the plugs to be shed. Aluminum salts also possess astringent properties, which further contributes to the temporary constriction of the sweat ducts. Antiperspirants are regulated as over-the-counter drugs because they are intended to affect the function or structure of the body by reducing the flow of sweat.
Presence in Food, Water, and Pharmaceuticals
Aluminum salts are widely present in the public water supply due to their role in the purification process. Water treatment facilities commonly use Aluminum Sulfate, or Alum, as a coagulant. When Alum is added to raw water, it neutralizes the electrical charges of suspended impurities like clay, silt, and microorganisms. This neutralization causes the tiny particles to clump together into larger, heavier masses called flocs, which are then easily removed through sedimentation and filtration.
Food Additives
Within the food industry, aluminum compounds serve a variety of technical functions as food additives. Sodium aluminum phosphate is a common component in commercial baking powders, where it acts as a leavening agent. Aluminum Sulfate can be used as a firming agent in certain pickled products or canned goods. Other aluminum compounds are used to create “lakes,” which are insoluble pigments that help stabilize coloring agents in various processed foods.
Medical Applications
In the medical field, aluminum salts are utilized in both oral and injectable forms. Aluminum Hydroxide is a long-used active ingredient in antacids, where it works to neutralize stomach acid and provide relief from heartburn and indigestion. Furthermore, aluminum salts, including Aluminum Hydroxide and Aluminum Phosphate, are incorporated into many vaccines as adjuvants. The adjuvant acts to enhance the body’s immune response to the vaccine’s antigen, typically by creating a physical depot that stimulates a stronger and more prolonged immune reaction.