Stearic acid is a chemical compound with the formula C18H36O2, part of the saturated fatty acid group. Its scientific name is octadecanoic acid. Fatty acids are organic substances that have a long structure made of carbon, without any branches, and a COOH group at the end. This is called the carboxyl group and consists of two separate parts, one made up of a hydrogen atom and an oxygen one, while the second is a double bond between atoms of oxygen and carbon.
Today, stearic acid is usually found mixed with palmitic acid. However, pure stearic acid is also commercially available. Industrially, it can be made by mixing triglycerides with extremely hot water with a temperature of more than 200°C. This turns the fats into soap and stearic acid can be isolated by distillation.
Stearic acid can be found as part of oils and fats in both plants and animals. However, animal fat is typically a lot richer and the content of stearic acid can even reach 30%. Most vegetal fats don't have more than 5% but shea and cocoa butter have a massive content of triglycerides of 30 and even 45%.
In nature, stearic acid is produced in a different way. Two carbon structures come from acetyl-CoA while the main process of synthesis of fatty acids in general starts from various types of carbohydrates.
Stearic acid is an ingredient in many industrial products and can be found in numerous household brands. It has hardening and lubricant properties but is especially used as an emulsifier because it makes it possible to mix oil and water. For this purpose it is included in many everyday products like cosmetics, soap, lotion, candles and solid deodorants. It plays a vital role in the composition of candles, increasing their melting point, strengthening the mix and making the wax more opaque.
In pure form, stearic acid actually looks like wax and is usually found as yellow or white flakes without any scent. It becomes a transparent liquid at higher temperatures. We eat a lot of stearic acid without knowing it, since it is an ingredient in bakery products, margarine and many other foods. It is also one of the most widespread fatty acids in nature and can be found in most oils and fats, especially cocoa butter and beef fat.
Almost all of the natural oils and fats, both vegetal and animal ones, have this very common fatty acid in their composition. The modern name of the compound actually comes from the ancient Greek word steatos, which meant beef fat (tallow). Its compounds, both esters and salts, are called stearates.
The commercial production of stearic acid is quite recent but the compound was known since ancient times. During the age of the pharaohs, Egyptians used a mix of stearic and palmitic acid as hair gel, to fix their hair in complicated styles. This gel has been found in many ancient tombs and was detected in the hair of mummies. It is also believed that ancient people discovered the industrial extraction of stearic acid by accident, when they tried to transform animal fats into oil and got soap instead. Both the ancient Egyptians and the Romans used stearic acid for its medical properties in the form of seeds and plants that were rich in this fatty acid.
Stearic acid is inexpensive to produce and has many industrial uses. It can be found as a softener in textiles, as a releasing agent in car tyres and in most types of automotive lubricants and oils.
The most important use of the compound is in cosmetics. The base of most creams, lotions and solid deodorants consists of stearic acid. It improves the structure of the mix and increases both its shelf life and stickiness on the skin. Stearic acid has a high melting point, so there is no risk of melting due to the skin temperature. This allows cosmetics to stay longer on the skin without decomposing or streaking.
The stability of stearic acid at high temperatures makes it a good ingredient for the food industry. It resists during both cooking and storage in the freezer. It is especially useful in the composition of margarine and other types of spreadable food. When ingested, the human body converts most stearic acid into a monounsaturated fat named oleic acid. This makes it safe for consumption since it will not increase the level of cholesterol, unlike other saturated fats.
This chemical can also inhibit oxidation, which opens up more industrial uses. It is a cheap coating for reactive metals in powder form, like the aluminum and iron used in fireworks. This greatly increases the shelf life of these products. For the same reason, it is included in some metal polishers designed to remove rust, in particular from tools.
It is one of the most important components of candles, since stearic acid can significantly increase their melting point while providing durability and strength to the mix.
It has many other commercial uses, due to its good properties and low cost. It can be found in metal polishes, moulds for injection, candy, ceramics, as well as fireworks. Since it acts as both an emollient and an emulsifier, it is a base for many products and can be converted into other fatty acids. It is a major component of many diverse products such as rubber softeners, crayons, candles, pills and plastics.
Stearic acid is widespread in nature and has been consumed by humans for a long time, without significant side effects. All of the major safety institutions have approved it use, for example the FDA allows it as an additive in food while a similar organization has validated it as a safe ingredient in cosmetics.
Even very high doses of stearic acid don't seem to be toxic for humans. Various modern studies have confirmed that it doesn't cause cancer or irritation and doesn't seem to have any side effects. Even pregnant women can consume stearic acid but medical advice is still a wise precaution, just in case.