PEG-40 Hydrogenated Castor Oil
What it is
PEG-40 Hydrogenated Castor Oil is a non-ionic emulsifier and solubilizer made by reacting hydrogenated castor oil with roughly 40 moles of ethylene oxide (a process called ethoxylation), which lets it blend water- and oil-based ingredients that don't naturally mix. It shows up across cosmetics and personal care products — wipes, lotions, fragrance bases — as an emulsifier, and the same molecule is also a common pharmaceutical excipient, sold industrially under trade names like Kolliphor RH 40 (formerly marketed as Cremophor RH 40) and listed in pharmacopeias as Polyoxyl 40 Hydrogenated Castor Oil, used to solubilize poorly water-soluble drugs in oral and topical formulations. The castor oil base itself is plant-derived and not the source of any concern; hydrogenation and ethoxylation are the standard, well-characterized industrial steps that turn it into this ingredient.
Why it's flagged
The concern isn't the finished molecule but a byproduct of how it's made. Ethoxylation can leave behind trace residues of unreacted ethylene oxide and can generate 1,4-dioxane as a side reaction. The Cosmetic Ingredient Review (CIR) Expert Panel's own 2014 safety assessment of PEGylated oils — which specifically covers PEG-40 hydrogenated castor oil — names this as a real concern, notes that the cosmetic industry uses additional purification (typically vacuum stripping) to limit it, and that levels around 10 ppm or below are achievable and considered safe by regulatory bodies that have reviewed cosmetic-grade dioxane exposure. Both impurities carry independently documented carcinogen classifications from bodies that had no involvement in the CIR review: the International Agency for Research on Cancer (IARC) classifies ethylene oxide itself as a Group 1 carcinogen (carcinogenic to humans) — a direct, DNA-reactive alkylating agent — a classification dating to 1994, and separately classifies 1,4-dioxane as Group 2B (possibly carcinogenic to humans), a 1999 evaluation based on liver, nasal, and other tumors across several animal species. The EU's harmonised CLP classification for 1,4-dioxane was tightened as of December 2022 to Carc. 1B, H350 ("may cause cancer"), and the U.S. National Toxicology Program lists it as reasonably anticipated to be a human carcinogen. Neither byproduct is a functional ingredient — they contribute nothing to what the product does — and how much of either ends up in a given batch depends entirely on the manufacturer's purification practices, which no label discloses.
How concerned to be
This is a genuinely context-dependent entry, and the honest reading cuts both ways. The body that specifically reviewed this ingredient — the CIR Expert Panel — concluded PEG-40 hydrogenated castor oil is safe as used in cosmetics at concentrations up to 100%, and that conclusion already accounts for the dioxane/ethylene-oxide issue, since the same panel is the one that flagged it and pointed to purification data showing trace levels are achievable. That's a meaningfully stronger basis than an ingredient nobody has scrutinized. Set against that: the safety conclusion is conditional on purification practices that vary by manufacturer and supplier and aren't verifiable from a finished-product label. Unlike sodium laureth sulfate (SLES), which the FDA has directly surveyed for dioxane contamination in finished cosmetic products across more than a decade of periodic testing, this search did not turn up a comparable dedicated testing survey of finished products formulated specifically with PEG-40 hydrogenated castor oil — that's a real data gap, not a documented hazard, and the distinction matters. The practical takeaway: this isn't an ingredient with a track record of contamination findings in finished baby products, but it's also not one where "safe" has been independently confirmed at the shelf level the way the raw ingredient has been reviewed on paper. Treat it the way you'd treat any PEG or ethoxylated ingredient on a label — a lower-priority concern than a documented hazard, worth favoring alternatives for when you have an easy choice, especially in leave-on products used repeatedly on infant skin, but not a reason to treat a product as unsafe on this ingredient alone.
What it's called on a label
Look for any of these on an ingredient list: Polyoxyl 40 Hydrogenated Castor Oil, Kolliphor RH 40, Cremophor RH 40, Macrogolglycerol Hydroxystearate, PEG-40 Hydrogenated Castor Oil.
Sources
- Safety Assessment of PEGylated Oils as Used in Cosmetics, Cosmetic Ingredient Review (CIR) Expert Panel, published in International Journal of Toxicology (2014)
- 1,4-Dioxane in Cosmetics: A Manufacturing Byproduct, U.S. Food and Drug Administration (FDA) (2022)
- Ethylene Oxide, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 60 (Group 1), International Agency for Research on Cancer (IARC/WHO) (1994)
- 1,4-Dioxane, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 71 (Group 2B), International Agency for Research on Cancer (IARC/WHO) (1999)
- 1,4-Dioxane — Harmonised Classification and Labelling (Carc. 1B, H350, effective Dec. 2022), European Chemicals Agency (ECHA) (2022)
- 1,4-Dioxane, Report on Carcinogens, Fifteenth Edition, National Toxicology Program (NTP), U.S. Dept. of Health and Human Services (2021)