Malic acid is a chemical found in certain fruits and wines. It is sometimes used as medicine. Malic acid is used most commonly for dry mouth. It is also used for fibromyalgia, fatigue, and skin conditions, but there is no good scientific evidence to support these other uses.Malic acid neutralizes the pH levels of the hair follicles and removes dirt deposits stuck to the hair. It can also prevent hair loss. Simply wash your hair with diluted apple cider vinegar (twice or thrice a week, before shampooing), which is a very good source of malic acid.