Steareth-20 is a synthetic compound that functions as a cleansing agent, a surfactant, and an emulsifier in a variety of cosmetics and personal care products.
The group of steareth ingredients are synthetic compounds that are created through a process known as ethoxylation, a chemical reaction in which ethylene oxide is added to a substrate. With steareth-20, the substrate is stearyl alcohol, a fatty alcohol that is derived from stearic acid. The number associated with the steareth (i.e. steareth-20) indicates the average number of repeating ethylene oxide units in the molecule. The steareth ingredients are waxy solids that can be used in cosmetics at concentrations of up to 25%.
Steareth-20 is added to cosmetics and personal care products because it functions as a cleansing agent, a surfactant, and an emulsifier.
Surfactant is the short term for surface active agent. Surfactants are compounds that lower the surface tension between two substances, such as two liquids or a liquid and a solid. In skin care products, surfactants work to degrease and emulsify oils and fats 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. Thus, surfactants attract the oil, dirt, and other impurities that have accumulated on your skin during the day and wash them away. Due to these properties, steareth-20 can be found in many different cleansers and body washes.
Steareth-20 has an HLB value of 15.3. 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.
Steareth-20 also functions as an emulsifier. An emulsifier is needed for products that contain both water and oil components, for example, when oils are added to a water-based formula. 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 steareth-20 can be added to the system, which helps the droplets remain dispersed and produces a stable emulsion.
As an emulsifier, steareth-20 consists of a water-loving hydrophilic head and an oil-loving hydrophobic tail. The hydrophilic head is directed to the aqueous phase and the hydrophobic tail to the oil phase. Once again, steareth-20 reduces the surface tension by positioning itself at the oil/water or air/water interface, which has a stabilizing effect on the emulsion.
The safety of the steareth ingredients (including steareth-20) has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The CIR Expert Panel evaluated the scientific data and concluded that these ingredients were safe as cosmetic ingredients in the present practices of use and concentration. In 2006, as part of the scheduled re-evaluation of ingredients, the CIR Expert Panel considered available new data on the steareth ingredients and reaffirmed the above conclusion.
Despite the approval of steareth-20 by the CIR Expert Panel, there are concerns about the presence of ethylene oxide in this ingredient. This is because the process of 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.”
According to EWG, steareth-20 has received an overall rating of 3 on a 1 to 10 scale, with 1 being the lowest health hazard and 10 being the highest. Once again, the concerns for this ingredient are due to the potentially toxic impurities such as 1,4-dioxane.
References: Wikipedia, “Ethoxylation”, Int J Toxicol. Nov 1988; 7(6) 881-910, Paula’s Choice, “Surfactant”, Dow, “What is HLB?”, EFEMA, “What is an emulsifier?”, Cosmetics Info, “Steareth-20”, Organic Consumers Organization, “1,4-Dioxane and Cosmetic Safety”, EWG’s Skin Deep Cosmetic Database, “Steareth-20”.