Malic Acid
Apple acid
No meaningful concern for most people; irritation is possible but rare.
Also written as: AHA · DL-Malic Acid · Hydroxybutanedioic Acid
What it is
Malic acid is an alpha hydroxy acid with two acid groups, found naturally in apples and other fruit; cosmetic grade is normally the synthetic DL form. It is a weaker exfoliant than glycolic or lactic acid and is most often used at low levels to buffer a formula to its target pH. When it does appear as an active, it is usually alongside other AHAs in a blend.
What it does well
Adds mild exfoliation and keeps the formula at the right pH
Its larger, less mobile molecule exfoliates less efficiently than glycolic acid, but it is a reliable buffering agent, which is why it appears near the end of most ingredient lists.
Limited evidence
Worth knowing
It is still an acid
In a low-pH blend it contributes to overall stinging, even though on its own at buffering levels it does very little.
Matters most toPeople with sensitive skin using multi-acid masks.
Where the EU stands
No specific restriction
Not listed in any Annex of the EU Cosmetics Regulation, so there is no legal maximum. The SCCNFP's precautionary advice on alpha hydroxy acids was framed around glycolic and lactic acid rather than malic acid.