Laureth-4 is a synthetic polymer that is used in many different cosmetics and personal care products as a surfactant and emulsifier.
Laureth ingredients are synthesized through a process known as ethoxylation, a chemical reaction in which ethylene oxide is added to a substrate. In this case, the substrate is lauryl alcohol. Lauryl alcohol is obtained from lauric acid, a saturated fatty acid with a 12-carbon atom chain that can be found in palm kernel oil or coconut oil. The number associated with the laureth (i.e. laureth-4) indicates the average number of repeating ethylene oxide units in the molecule. Laureth-4 is a clear, colorless liquid. As the numerical value of laureth ingredients increases, the viscosity increases until they become white, waxy solids.
In cosmetics and personal care products, laureth-4 functions as a surfactant and emulsifier. It can be found in products such as bath, cleansing, hair, and sunscreen products. It is also used in cuticle softeners, deodorants, and moisturizing products.
As a surfactant, laureth-4 works by lowering the surface tension between two substances, such as two liquids or a liquid and a solid. A surfactant molecule contains one end that is hydrophilic (attracted to water) and one end that is lipophilic (attracted to oil). This allows surfactants to attract and suspends oils, dirt, and other impurities that have accumulated on the skin and wash them away. Due to these properties, laureth-4 can be found in many different cleansers and body washes.
Laureth-4 is also an emulsifier with an HLB value of 9.7. HLB (Hydrophile-Lipophile Balance) is an empirical expression for the relationship of the hydrophilic and lipophilic groups of a surfactant. An HLB of less than 10 means that the substance is soluble in oil. Low HLB emulsifiers such as laureth-4 give rise to water-in-oil emulsions.
Emulsifiers are necessary when a formulation contains both water and oil components. Mixing water and oil together creates a dispersion of oil droplets in water (and vice versa). However, these two phases can separate if the product is left to settle. To address this problem, an emulsifier like laureth-4 can be added to the system to help the droplets remain dispersed. Emulsifiers improve the consistency of a product, which enables an even distribution of topical skin care benefits.
The Cosmetic Ingredient Review (CIR) Expert Panel evaluated the scientific data and concluded that the laureth ingredients were safe as used in cosmetic products only when formulated to be non-irritating. This is because the laureth ingredients have the potential to irritate the skin.
Even though laureth-4 is considered a safe cosmetic ingredient by the CIR Expert Panel, there are concerns about the presence of ethylene oxide in this ingredient. As mentioned above, laureth-4 is created through ethoxylation, a process that produces 1,4-dioxane as a byproduct. 1,4-dioxane is a known animal carcinogen that penetrates readily into the skin. According to the National Toxicology Program, “1,4-dioxane is reasonably anticipated to be a human carcinogen.” It 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.”
However, the potential presence of 1,4-dioxane can be controlled through purification steps to remove it before blending laureth-4 into cosmetic formulations.
References: Wikipedia, “Dodecanol”, Cosmetics Info, “Laureth-4”, Organic Consumers Organization, “1,4-Dioxane and Cosmetic Safety”.