Isostearic Acid
Explained
Isostearic Acid is a fatty acid and a structural cousin of stearic acid. It is an emulsifier.
The branched structure of this ingredient enhances fluidity and gives it a lighter, less greasy feel compared to other fatty acids. It helps improve texture and consistency because it prevents oil and water phases from separating.
This ingredient is sourced from plant-based oils like soybean or rapeseed.
Clinical studies found no signs of irritation from this ingredient.
Since Isostearic Acid is an 18-carbon fatty acid, it is in the range that Malassezia can feed on. This ingredient may not be fungal acne safe.
You might have seen sources that this ingredient is comedogenic. This is because the original comedogenic tests (on rabbit ears, which are more sensitive than human skin) tested
The Kligman/Fulton rabbit ear papers actually tested the ester, Isopropyl Isostearate and not Isostearic acid itself. There has been no comedogenic testing done on this ingredient, but it may be worth patch testing if you have acne-prone skin.
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