Lactic acid is a common ingredient in cosmetics, where it's used for its exfoliating and moisturizing properties, and to adjust the pH of the formula. It's a mild alpha-hydroxy acid (AHA) that's derived from lactose, a carbohydrate found in milk. Lactic acid is a component of the skin's natural moisturizing factor (NMF), which helps the skin retain moisture. 

Lactic acid can help with a variety of skin concerns, including: 

• Anti-aging: By promoting skin cell turnover, lactic acid can improve the skin's appearance and texture. 
• Acne: Lactic acid can help treat moderate skin conditions like acne. 
• Rough and bumpy skin: Lactic acid can help smooth rough areas and eliminate dead skin cells. 
• Hyperpigmentation: Lactic acid can help treat hyperpigmentation. 

Lactic acid is available in over-the-counter cosmetics, but products with stronger concentrations may require a prescription from a doctor. Products for home use typically contain 10% or less lactic acid, while products with more than 10–15% require professional application.