What it is
Malic Acid is a dicarboxylic alpha-hydroxy acid found in apples and other fruits. In sunscreen and skincare formulas it is most often used in small amounts to adjust and buffer pH, while at higher concentrations it can provide gentle exfoliation. It is not a UV filter.
Safety & warnings
At the low levels used for pH adjustment it is well tolerated. As an alpha-hydroxy acid at exfoliating concentrations and low pH it can cause stinging or irritation on sensitive or compromised skin, and AHA use can increase skin sensitivity to sunlight, so sun protection is advisable. It is not considered comedogenic.
Origin & sourcing
Can be naturally occurring (notably in apples) or produced synthetically; the cosmetic ingredient is commonly manufactured.
History
Malic acid was first isolated from apple juice in the eighteenth century, which is the basis of its name.
Questions everyone asks
What is malic acid used for in sunscreen?
It is most often used in small amounts to adjust and stabilize the product's pH rather than as an active exfoliant.
Is malic acid an exfoliant?
It can be, at higher concentrations and low pH, since it is an alpha-hydroxy acid; in many formulas it functions only as a pH adjuster.