Lecithin describes a natural substance made up of fatty acids that functions as an emollient, emulsifier, and penetration enhancer when added to formulations of cosmetics and personal care products.
Lecithin is a generic term that describes any group of yellow-brownish fatty substances that naturally occur in plant and animal tissues, as well as in the human body. It’s made up of fatty acids, typically a mixture of the diglycerides of stearic, palmitic and oleic acids, linked to the choline ester of phosphoric acid. Lecithin fats are amphiphilic, which means they attract both water and fatty substances (they are hydrophilic and lipophilic).
Lecithin was first isolated in 1845 by the French chemist and pharmacist Theodore Gobley from egg yolk. It can also be derived from sources such as soybeans, milk, marine sources, rapeseed, cottonseed, and sunflower.
Lecithin can be used for smoothing food textures, dissolving powders (emulsifying), homogenizing liquid mixtures, and repelling sticking materials. Lecithin is also sold as an over-the-counter dietary supplement that is said to help improve the strength and function of the heart, aid cognitive functions like memory retention and logical reasoning, and might also reduce inflammation and internal swelling.
In cosmetics and personal care products, the kind of lecithin used is called hydrogenated lecithin. Hydrogenated lecithin is the product of controlled hydrogenation (addition of hydrogen) of lecithin.
In cosmetics and personal care products, lecithin functions as an emollient, an emulsifier, and as a penetration enhancer.
As an emollient, topically applied lecithin has the ability to soften and soothe the skin. Its high concentration of fatty acids creates a barrier on the skin that effectively seals moisture in while keeping air and other environmental elements out. This property makes lecithin an excellent ingredient to add to restorative creams, or for products designed for mature, dry, or overworked skin. Additionally, lecithin is commonly used in hair conditioners and other hair products due to its emollient properties.
Even though lecithin has a low solubility in water, it functions as an excellent emulsifier. An emulsifier is needed for products that contain both water and oil components. According to EFEMA, when water and oil are mixed together and vigorously shaken, a dispersion of oil droplets in water – and vice versa – is formed. When shaking stops, however, the two phases start to separate. To address this problem, an emulsifier like lecithin can be added to the system to stabilize the emulsion.
Lecithin can also be classified as a penetration enhancer. This means it has the ability to deeply penetrate through the layers of skin, enhancing the penetration of other active ingredients. In aqueous solution, its phospholipids can form liposomes, a spherical structure in which the acyl chains are inside and not exposed to the aqueous phase. According to an article published in the International Journal of Toxicology, liposomes are considered effective in capturing other compounds inside their spherical structure and delivering any such captured compound through the skin barrier. This property of lecithin is also utilized by the pharmaceutical industry to enhance the penetration of a drug through the skin and across other biological membranes, such as intestinal, buccal, rectal, and nasal.
The Food and Drug Administration (FDA) includes lecithin on its list of substances affirmed as Generally Recognized As Safe (GRAS) for direct addition to food.
The safety of lecithin and hydrogenated lecithin has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The CIR Expert Panel evaluated the scientific data and concluded that lecithin and hydrogenated lecithin are safe as used in rinse-off products. However, the CIR Expert Panel limited the use of lecithin and hydrogenated lecithin in leave-on products to concentrations less than or equal to 15 percent.
Since lecithin functions as a penetration enhancer, caution should be exercised when it is combined in formulations that contain other ingredients that can be harmful if absorbed through the skin barrier.
It is possible for some people to have allergies to lecithin since it can be derived from soybeans, eggs, and milk, which are common allergenic foods. Those that are highly sensitive to these foods might react to lecithin.
References: Wikipedia, “Lecithin”, Healthline, “Lecithin Benefits”, Int J Toxicol. 2001;20 Suppl 1:21-45, Cosmetics Info, “Lecithin”, WiseGeek, “What are the benefits of lecithin?”, EFEMA, “What is an emulsifier?”