Lactic acid is made from sour milk and is considered to be a milder peel than glycolic acid.

When a lactic acid peel is applied to the skin, the lactic acid particles penetrate the skin and help to kill germs and bacteria. Lactic acid also helps to reduce the bonds that hold dead skin cells to the skin, which can help to reduce age spots. Glycolic acid works similarly to release dead skin cells, but is slightly smaller in terms of molecule size, which means the peel may penetrate slightly deeper, according to 30% Glycolic. Because of this, glycolic acid reaches the dermis, which is the layer of skin underneath the epidermis. There, the glycolic acid stimulates collagen production, which can make the skin appear tighter.