EWG Safety Score
2
Low
What Is Isostearic Acid?
Isostearic acid is a branched-chain fatty acid — in practice a mixture of methyl-branched C18 acids — made industrially from oleic acid by rearranging its carbon chain and then hydrogenating it.
The branching is what matters. Straight-chain stearic acid is a waxy solid, while isostearic acid stays liquid at room temperature, so it can do a fatty acid's job without adding waxy drag to a formula.
In a product it works as an emulsifier, and once neutralised in a formula it also acts as a cleansing agent. It is a formulation ingredient rather than an active — it shapes how a product feels and behaves rather than changing skin itself.
How It Works
Like all emulsifiers, it has a water-loving end and an oil-loving end. Sitting at the boundary between the two, it stops them separating into layers, which is what keeps a cream or lotion uniform from first use to last.
Once neutralised into its salt form, the same structure gives it cleansing action: the oil-loving end attaches to sebum and residue, the water-loving end lets it rinse away. Because the molecule is branched rather than straight, it does this without the waxy drag a straight-chain fatty acid would leave.
Clinical Evidence & References
Published Research
-
4 Final Report on the Safety Assessment of Isostearic Acid, International Journal of Toxicology, 1983, pages 103-116 4 Final Report on the Safety Assessment of Isostearic Acid, 1983
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A conditioning agent derived from hydrolysed collagen, designed to improve skin and hair texture
Isostearoyl Hydrolyzed Keratin
A keratin-derived conditioning agent that strengthens and smooths hair and skin
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A water-soluble jojoba derivative that conditions without a greasy feel
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