Calcium stearate is a non-toxic, white powdery substance. It is a calcium salt derived from stearic acid and is widely used in cosmetics, plastics, and pharmaceuticals. This salt is used as a plasticizer, stabilizer, and surfactant. It is a substance that the U.S. Food and Drug Administration has generally recognized as safe when used as a food additive.
When certain types of fatty acids are heated with an alkaline substance, the resulting salt is known as soap. Stearic acid is one of the most widely used components of soaps. Calcium stearate is a synthetic ingredient formed through a reaction when stearic acid and calcium oxide are heated together. It is the most important type of calcium salt, but due to its lack of solubility, it is not commonly used in soap in modern times, having been replaced by synthetic substances that are water soluble.
This substance is frequently found in cosmetics, however, especially aerosol hair styling products. It is also found in cosmetic powders, ointments, and packaging. Despite a very low risk for dermal irritation, topical contact may cause redness, itching, and eye irritation.
Calcium stearate was first used in 1924 to improve the texture of bread dough and reduce dust levels in flour, and its unique properties made it useful in many non-food industries as well. The substance reduces friction when added to other materials, increasing flow rate and preventing caking. It may also be used in gels or to add bulk to cosmetic powders. In addition to its insolubility in water, it is also insoluble in acetone, ether, and cold alcohol.
Vegetarians and vegans may avoid cosmetics containing this salt because it may be derived from stearic acid made from animal sources. Virtually all that is produced in the United States is derived from stearic acid made from plant oils, like coconut oil or palm oil, but sometimes beef tallow may be used. Other countries may derive stearic acid from cottonseed, soybean, or other plant oils.
Calcium stearate is responsible for the scum formed when some soaps are used in hard water. When a soap containing sodium stearate is used in hard water, it will react with calcium ions in the water to form this scum. This substance is responsible for rings in bath tubs and leaves an undesirable coating on hair and skin after bathing.