Done correctly, exfoliation helps your skin purge dead cells, revealing a better complexion underneath. Exfoliation happens primarily in the outer layer of your skin, the stratum corneum. The dead skin cells there should shed in a process called desquamation, but it is slowed by a number of factors: hormone fluctuations, sun exposure, vitamin deficiencies and aging. Exfoliation, either mechanical or chemical, accelerates the shedding process, and when done right, reveals healthy skin cells. Chemical exfoliations use fruit enzymes, or acids like glycolic acid, derived from sugar, and lactic acid, which is made from milk. Mechanical exfoliations use beads, brushes and razors (dermaplaning) to lift dead cells of the skin. Chemical exfoliations gently break the bonds that hold dead skin cells together, so they can be easily rinsed away. But for skin with a history of irritation or allergy from cleansers and lotions, mechanical is the way to go.