Chapter 2: Other surfactants · Part 4: Soap
Sodium oleate, potassium oleate, sodium stearate and sodium laurate
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The worst fact: "most household and body soaps have an alkaline pH (9-12)", and in a test of 29 cleansers and soaps, irritation rose with pH. After washing, skin can take "up to several hours" to get back to its normal pH.
Why brands use it: these are the individual soap molecules: oleate from animal or vegetable fats, stearate often from hardened (hydrogenated) fats, laurate from coconut oil.
Take care if: you make soap at home. Caustic soda (lye) as sold is a Schedule 6 Poison (weak solutions of 5% or less are Schedule 5). In a Ghana study, half of 57 young children who swallowed caustic soda did so during soap-making (under-5s at one Accra hospital), and in 2020 a US supplier recalled about 329,000 containers of lye (sodium and potassium hydroxide) sold for soap-making and clearing drains because the packaging wasn't child-resistant; one child had chemical burns to the mouth.
Comes from: fatty acids split from animal or vegetable fats, neutralised with caustic soda or potash.
Myth check: "Soap works because it kills germs": mostly it lifts them off your skin so they rinse away (it can also break apart some viruses' fatty outer coat), which works. The US FDA says there isn't sufficient evidence that antibacterial soaps prevent illness better than plain soap and water, and in 2016 banned 19 antibacterial ingredients, including triclosan, from consumer hand and body washes.
Contaminants: nil. (Badly made soap can carry leftover caustic soda; see sodium tallowate.)
Fair to say: international food-additive experts (JECFA) set no numerical daily limit for sodium oleate ("ADI not specified"), and simple household soaps are "less lethal than synthetic anionic detergents & even less than most nonionic detergents". All four are green circles on the US EPA's Safer Choice list.
We use this ingredient. Potassium oleate is the olive-oil half of the castile soap in our cleaning sprays and Castile Hand Wash. In our Laundry Liquid and Wool Mix, it comes from the oleic acid in the soap.
Correct as of November 2026. What the badges mean
Sources
- US CPSC. Lye recall (2020).
- HSDB (US National Library of Medicine), via PubChem, including Gosselin, Clinical Toxicology of Commercial Products (1984); ECHA C&L Inventory (company notifications, via PubChem); JECFA, sodium oleate (via PubChem).
- HERA. Alcohol ethoxylates (2009); esterquats (environment 2008, human health 2009); cocamidopropyl betaine (2005); fatty acid salts (2002).
- Cosmetic Ingredient Review: alkyl glucosides (2013); poloxamers (2008); cocamidopropyl betaine and amidopropyl betaines (2012); alkyl betaines (2018); alkyl sultaines (2024); lauriminodipropionates (2013); coconut oil and related ingredients (2011); fatty acids and fatty acid salts (2019).
- Tupker RA et al. Irritancy of sodium laurate. Skin Res Technol 1997, PMID 27333375.
- Botwe BO et al. Caustic soda ingestion in children, Ghana. BMC Res Notes 2015, PMID 26576563.
The full source list is at the end of Chapter 2.