Lactic acid is derived from milk and works as a form of alpha hydroxy acid, says the University of Maryland Medical Center. It's sometimes added to facial skin care peels, which are designed to be smeared onto your skin and left on for a certain amount of time before being washed off. Such peels are popular due to their benefits for your skin's overall health.
Melanin is your skin's pigment. Overproduction, often attributed to your skin's exposure to the sun, can lead to discolorations like brown spots or splotches. Lactic acid at a strength of 4 to 10 percent can help "directly inhibit melanin formation," creating a "formidable" tool for lightening or removing skin discolorations.