PEG-40 hydrogenated castor oil is a modified version of natural castor oil used primarily as an emulsifier, solubilizer, and surfactant in cosmetics and personal care products. Its main job is helping oil-based ingredients like fragrances, essential oils, and vitamins dissolve evenly into water-based formulas. You’ll find it on ingredient lists for everything from facial cleansers and shampoos to lotions and perfumed body sprays.
How It’s Made
The ingredient starts as regular castor oil, which comes from the seeds of the castor plant. That oil goes through two chemical modifications. First, it’s hydrogenated, a process that adds hydrogen atoms to make the oil more stable and solid at room temperature (the same basic process that turns liquid vegetable oil into margarine). Then it undergoes ethoxylation, where units of polyethylene glycol (PEG) are attached to the oil molecules.
The “40” in the name refers to the average number of PEG units attached to each castor oil molecule. More PEG units make the ingredient more water-friendly. With 40 units, this version has a high HLB (hydrophilic-lipophilic balance) value of 15, which means it strongly favors water. That’s what makes it so effective at pulling oils into water-based products and keeping them mixed.
What It Does in Products
PEG-40 hydrogenated castor oil is a multitasker. Its primary roles include:
- Solubilizer: It dissolves fragrances, essential oils, and oil-soluble vitamins into water-based formulas so they don’t separate or float on top.
- Emulsifier: It helps oil and water phases stay blended in creams, lotions, and serums, creating stable, uniform textures.
- Surfactant and foam booster: In cleansers and shampoos, it helps lift dirt and oil from skin and hair, and can enhance lather.
Because it’s miscible in both water and oils, formulators can use it across a wide range of product types. It shows up frequently in micellar waters, toners, and leave-on products where you need fragrance or botanical extracts evenly distributed through a clear, water-based formula.
Skin Benefits
Beyond its formulation duties, PEG-40 hydrogenated castor oil has mild emollient properties. The molecule is too large to penetrate past the skin’s surface, but that’s actually useful. Sitting on top of the skin, it forms a light barrier that minimizes moisture loss and leaves skin feeling soft. It’s not a powerhouse moisturizer on its own, but it contributes to the overall feel and hydration of a product.
Safety Profile
PEG-40 hydrogenated castor oil has been reviewed multiple times by the Cosmetic Ingredient Review (CIR) Expert Panel, the independent body that evaluates cosmetic ingredient safety in the United States. In 1997, the panel concluded it was safe for use in cosmetics at concentrations up to 100%. A broader 2012 reassessment covering 130 related PEGylated oils reaffirmed that finding, with the condition that products be formulated to be non-irritating.
Irritation and sensitization testing specific to this ingredient has been reassuring. In one study, a microemulsion containing 20% PEG-40 hydrogenated castor oil applied to skin produced no signs of redness or irritation over six days of observation. A separate study using a gel system with roughly 21% of the ingredient found the same result, with microscopic examination of the skin confirming no irritation at the cellular level. Clinical data across the broader family of PEGylated castor oils showed little to no irritation or sensitization in both animal and human studies.
Potential Contaminants to Know About
The ethoxylation process used to make any PEG-based ingredient can produce trace impurities, specifically 1,4-dioxane, ethylene oxide, and propylene oxide. All three are recognized carcinogens, which understandably raises concern when people spot them in safety literature. The important context: these are manufacturing byproducts, not intentional ingredients, and reputable cosmetic manufacturers are expected to purify them out before the ingredient goes into a product.
The CIR panel emphasized that purification is a necessity, setting guideline limits of no more than 1 part per million (ppm) for 1,4-dioxane and 5 ppm for ethylene oxide and propylene oxide. At those trace levels, the panel maintained its safety conclusions. If this concerns you, choosing products from established brands that follow good manufacturing practices is the most practical way to minimize exposure, since these companies routinely test for and remove these impurities.
Where You’ll See It on Labels
You may also see this ingredient listed as polyoxyl 40 hydrogenated castor oil, macrogolglycerol hydroxystearate, or castor oil hydrogenated polyethoxylated. These are all the same thing. It appears in skincare, haircare, body care, and color cosmetics. In pharmaceutical products, it sometimes serves as an excipient to help deliver active ingredients. The concentrations used in consumer products typically fall well below the tested safe limits, and its long track record in both cosmetic and pharmaceutical formulations makes it one of the more thoroughly evaluated emulsifiers on the market.