"Apple acid" typically refers to malic acid, a naturally occurring alpha-hydroxy acid (AHA) found in apples and other fruits. Malic acid is used in skincare products for its exfoliating properties. Scientific studies and dermatological texts support the use of AHAs, including malic acid, for improving dry and flaky skin. AHAs work by loosening the bonds between dead skin cells, promoting their shedding and revealing fresher, more hydrated skin beneath. This process can help alleviate dryness and improve skin texture.

While glycolic and lactic acids (other AHAs) are more extensively studied, malic acid is included in several cosmetic formulations and has demonstrated similar exfoliating and humectant effects. For example, a 2004 clinical study found that topical AHAs improved skin hydration and reduced flakiness by enhancing the stratum corneum’s water-binding capacity. Malic acid is milder than some other AHAs, making it suitable for sensitive or dry skin types when used at appropriate concentrations.

However, there is less direct clinical research on malic acid alone compared to other AHAs, which is why the evidence rating is moderate. The support for its use is based on its chemical similarity to better-studied acids and its inclusion in effective multi-acid cosmetic formulations for dry or flaky skin.