Malic acid comes from apple and is an AHA. If these magic three letters don’t tell you anything, click here and read our detailed description on glycolic acid, the most famous AHA.
So malic acid is an exfoliant, that can - just like other AHAs - gently lift off the dead skin cells of your skin and make it more smooth and fresh.
There is not much research out there about malic acid itself. We could find one comparative study, that compared the effectiveness of glycolic acid, lactic acid, citric acid and malic acid. The first two ones were the winners while malic and citric acid were less effective.