Malic acid is a type of alphy hydroxy acid found naturally in all fruits and some vegetables. Malic acid preparations can also be purchased for oral and topical use. Individuals often use malic acid orally along with magnesium in order to ease the pain and tenderness associated with fibromyalgia. Another common use for malic acid is as a topical agent to treat various skin conditions. It is important to use careful consideration when it comes to the dose of malic acid used.