Household andIndustrial Uses.

Malic acid is commonly found in tart fruits and drinks; it's the substance that gives them their sour taste. However, it is not just a chemical that makes things taste sour--it also can be prescribed by your doctor for certain applications and used by your dentist to assist in filling cavities, in addition to being an active ingredient in many makeup and skin care products, making malic acid a very versatile substance. Always check with your doctor before using malic acid, as it can cause adverse effects when interacting with other drugs.

http://www.livestrong.com/article/28688-uses-malic-acid/