PEG-40 hydrogenated castor oil is a combination of synthetic polyethylene glycol (PEG) with natural castor oil. It is produced through a process called ethoxylation, a chemical reaction in which ethylene oxide is added to a substrate (in this case, castor oil). Castor oil is reacted with 40 units of ethylene oxide (hence the 40 in this ingredient’s name).
Castor oil is a vegetable oil obtained by pressing the seeds of the castor oil plant (Ricinus communis). Oils, also known as triglycerides, are esters derived from glycerol (aka glycerin) and three fatty acids. The fatty acid chains present in castor oil are approximately 90% ricinoleic acid, with oleic and linoleic acid also being significant components. Castor oil is a colorless to very pale yellow liquid with a distinct taste and odor.
PEG-40 hydrogenated castor oil is universally applicable in the beauty industry, especially in liquid soaps, lotions, body washes, shower gels, hair shampoos, facial cleansers, bubble baths, and decorative cosmetics.
In cosmetics and personal care products, PEG-40 hydrogenated castor oil functions as a surfactant, emulsifier, and emollient.
PEG-40 hydrogenated castor oil is a nonionic surfactant. Nonionic surfactants have a neutral charge. As a surfactant, PEG-40 hydrogenated castor oil works to lower the surface tension between two substances, such as two liquids or a liquid and a solid. Surfactants also degrease oils and suspend soil, allowing them to be washed away. This is possible because while one end of the surfactant molecule is attracted to water, the other end is attracted to oil. Due to these properties, PEG-40 hydrogenated castor oil can be found in many different cleansers and body washes.
PEG-40 hydrogenated castor oil is an emulsifier with an HLB value of 15. HLB (Hydrophile-Lipophile Balance) is an empirical expression for the relationship of the hydrophilic (“water-loving”) and hydrophobic (“water-hating”) groups of a surfactant. An HLB of greater than 10 means that the substance is soluble in water. Thus, PEG-40 hydrogenated castor oil can be used to make oil-in-water (o/w) emulsions.
As an emulsifier, PEG-40 hydrogenated castor oil is a useful ingredient for products that contain both water and oil components. 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. An emulsifier like PEG-40 hydrogenated castor oil can be added to the system to help the droplets remain dispersed. This improves the consistency of a product, which enables an even distribution of topical skin care benefits.
Lastly, PEG-40 hydrogenated castor oil functions as an emollient, which is why you can find it in many creams, lotions, and hair care products. Emollients work to soften and soothe the skin (or hair) while also acting as occlusive agents. Upon application, occlusive agents form a protective film on the surface of skin, which helps to prevent evaporation of the skin’s natural moisture. Over time, this increases skin hydration by causing buildup of water in the stratum corneum (the uppermost layer of skin).
The safety of PEG hydrogenated castor oils has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The Panel evaluated the scientific data and concluded that PEG-40 hydrogenated castor oil was safe for use in cosmetics at concentrations up to 100%.
Despite the approval of PEG-40 hydrogenated castor oil by the CIR Expert Panel, there are concerns about the presence of ethylene oxide in this ingredient. The process of making this ingredient, called ethoxylation, may lead to contamination with 1,4-dioxane, a potentially dangerous by-product. In fact, 1,4-dioxane is a known animal carcinogen that penetrates readily into the skin. This ingredient has also been linked with skin allergies.
The Organic Consumers Organization released a fact sheet on 1,4-dioxane based on information from the Campaign for Safe Cosmetics. The fact sheet outlines facts versus myths regarding 1,4-dioxane in personal care products. One concerning fact is that the levels of 1,4-dioxane found in many personal care products are 1,000 times higher than those found to cause cancer in animal studies. They add that according to the FDA, “Skin absorption studies demonstrated that dioxane readily penetrates animal and human skin from various types of vehicles.”
References: Wikipedia, “Castor Oil”, Dow, “What is HLB?”, Cosmetic Ingredient Review, “Amended Safety Assessment of PEGylated Oils as Used in Cosmetics”, 2012, Organic Consumers Organization, “1,4-Dioxane and Cosmetic Safety”.