EWG Risk Score:
What is it:
Stearic acid is a naturally-ocurring saturated fatty acid that is found in many natural oils like palm, coconut, and butters. To extract the stearic acid, an oil is processed under high heat and pressure and undergoes a process called hydrolysis. This breaks apart the oil molecules in to their separate fatty acids chains and also separates out the glycerol (aka glycerin.) Some stearic acid is derived from animal fats. PETA states: "When animal-derived, a fat from cows, pigs, and sheep and from dogs and cats euthanized in animal shelters, etc. May also be of plant origin, including from cocoa butter and shea butter. Can be harsh, irritating." (Source)
Is it a risk?
Animals who digested small amounts of stearic acid showed neurological side effects as well as organ system toxicity. In addition, low doses created skin irritation in lab tests. (Source)
Stearic acid is a naturally-ocurring fatty acid in many oils and fats in, in cosmetic use, really doesn't have many side effects. It can be comedogenic for some people, and an irritant for others. But it really depends on that person's sensitivities and the particular formulation. Most of the natural companies say their stearic acid is "made from coconut oil" but unless the product specifies, it's most likely animal-derived. Animal waste--the stuff that slaughterhouses can't use, the stuff that's not even good enough to make it in to hot dogs--are sent to places called rendering plants. Sometimes animal shelters will send euthanized dogs and cats to rendering plants as well. (Source) The dead carcasses and parts are separated meat from fat, bone from skin, and so on. The fat is then used to create cosmetic ingredients such as stearic acid.