"Apple acid" typically refers to malic acid, a naturally occurring alpha-hydroxy acid (AHA) found in apples and other fruits. AHAs, including malic acid, are commonly used in cosmetic dermatology for their exfoliating properties. The scientific rationale for using malic acid in treating or reducing the appearance of wrinkles is based on its ability to promote exfoliation of the stratum corneum (outermost skin layer), increase cell turnover, and stimulate collagen production. These actions can lead to smoother skin texture and a reduction in the appearance of fine lines and superficial wrinkles.

Several small clinical studies and reviews of AHAs show moderate evidence for the efficacy of glycolic, lactic, and malic acids in improving skin texture and diminishing signs of photoaging, including wrinkles. For example, a review published in the Journal of Clinical and Aesthetic Dermatology (2013) highlights that malic acid, when used in chemical peels or topical formulations, can improve skin hydration, elasticity, and reduce mild wrinkles. However, most studies group malic acid with other AHAs rather than studying it in isolation, and the majority of research focuses on glycolic and lactic acids.

In summary, there is moderate scientific support for the use of apple-derived malic acid in cosmetic products targeting wrinkles, primarily as part of AHA blends, but high-quality, malic-acid-specific clinical trials are limited.