Lactic Acid

Lactic acid is presumably one of the oldest actives. Women have noticed that it has some excellent uses for the skin. Many legends have it that Cleopatra bathed in sour milk in ancient Egypt. Yes, your assumptions are correct: sour milk is a primary natural source of lactic acid. 

As an AHA, lactic acid gently lifts away dead skin cells unveiling the more reinvigorated, silkier, and softer skin underneath. This fantastic property makes it the second most popular AHA among women. 

Lactic acid has larger molecules that penetrate the skin less efficiently than glycolic acid. Although the anti-aging properties of lactic acid are not as effective as those of glycolic acid, it is much more gentle on your skin. 

Studies show that lactic acid exhibits excellent anti-aging properties when used in the right concentration and properly balanced pH. However, its collagen-boosting abilities have not been confirmed. 

A 1996 study compared various levels of lactic acid concentration in skincare regiment and its effect on the outer and inner layers of the skin. Testing 5% and 12% lactic acid treatment over six weeks revealed that both treatments improved skin firmness and thickness and reduced the appearance of wrinkles. The results show that 5% of treatments affected the epidermis; the stronger solution affected both the outer and inner layers of skin. 

Lactic acid is often used in skin care products for its magical moisturizing properties. In fact, lactic acid is ideal for treating and moisturizing dry skin and is approved by the FDA as a prescription product called LacHydrin.