What is Isostearic Acid?
Isostearic Acid is a fatty acid. A branched C18 fatty acid used in emollient esters, named on comedogenic lists in the moderate range.
You may see it on labels as Isostearic Acid, Isostearate, so it can hide under more than one name in an ingredient list.
Where Isostearic Acid shows up
You'll most often find Isostearic Acid in cleansers, cream bases, and bar soaps, where it builds texture and lather. Separately from clogging, its irritancy is rated 0/5 — low, so it's unlikely to sting or sensitise on its own.
Is Isostearic Acid bad for acne-prone skin?
A moderate rating means Isostearic Acid clogs some people and not others. If you're prone to congestion, patch-test a product that features it prominently before committing.
Worth flagging: Isostearic Acid's rating is disputed. Credible sources land on different numbers, which is why we show a range rather than a single score — and why your own experience is the best tiebreaker.
Note for fungal-acne (malassezia) sufferers: Isostearic Acid is commonly avoided in fungal-acne routines, since it falls into the fatty-acid or ester families the yeast can feed on. The evidence there is looser than for comedogenicity — see our fungal-acne checker for context.
Non-comedogenic alternatives
If you're avoiding Isostearic Acid, these lower-risk ingredients serve a similar role and are gentler on pore-prone skin: