Lactic acid is produced by the body especially during high-intensity exercise. Bacteria also produce it by the fermentation of lactose, a sugar found in milk. In addition, lactic acid is found in fermented dairy products like cottage cheese, kefir and yogurt. As a result, lactic acid is often referred to as milk sugar. It’s lactic acid that gives sour dough bread its distinctive flavor and fermented foods such as sauerkraut, kimchi and pickled vegetables their mouth-puckering sourness. Lactic is approved by the FDA to be used as a food additive. In the medical and pharmaceutical industries, lactic acid serves as a starting point for making other compounds. Lactic acid is also added to some detergents, inks and lacquers due to its superior scum-busting power.
In the cosmetics and skin care industry, lactic acid is classified as an alpha-hydroxy-acid. Alpha-hydroxy-acids are natural acids derived from fruit and milk that have keratolytic properties when applied topically. As keratolytics, they help to slough off dead skin cells from the outer surface of the skin so that healthier cells can be revealed. Research shows that alpha-hyroxy-acids like lactic acid improve skin texture and reduce the appearance of fine lines and wrinkles. Lactic acid also increases skin thickness and firmness, giving it a more youthful appearance. There’s some evidence that it penetrates the dermal layer of the skin where it boosts the synthesis of collagen and elastin, two proteins important for youthful-looking skin. In addition, it helps to lighten areas that are darkly pigmented as a result of sun damage. That’s why lactic acid is an ingredient in some anti-aging skin care products.
Lactic acid helps skin retain moisture and has been used as a moisturizer to treat dry, itchy skin for over seventy years. It functions as a humectant, an agent that attracts and holds onto water. It has the added benefit of filling in the spaces between skin cells in the outer layer of the epidermis called the stratum corneum. This helps to reduce roughness and make skin feel softer and smoother. It’s a particularly good moisturizing ingredient for skin damaged by exposure to the sun.
Dermatologists and aestheticians use alpha-hydroxy-acids like lactic acid at concentrations of up to 70% to do superficial skin peels to remove dead skin cells, improve fine lines and wrinkles and lighten skin discolorations, while concentrations of lactic acid at concentrations of 10% or less are available in skin care products for home use. Daily use of lactic acid containing products helps to loosen and slough off dead skin cells to improve skin texture and soften the appearance of fine lines and wrinkles. Some products that may contain lactic acid include moisturizers, facial cleansers, conditioners and anti-aging treatments. Lactic acid is also used to adjust the pH of some cosmetic and personal care products.
Is lactic acid a safe ingredient in cosmetic and personal care products? The Food and Drug Administration (FDA) classifies lactic acid as “generally recognized as safe” as a food additive and recognizes it to be safe in cosmetic products for home use at concentrations of 10% or and concentrations of up to 30% in salon skin care products. Some people experience redness, flaking, stinging and irritation when they first start using products containing lactic acid or other alpha-hydroxy-acids. This becomes less pronounced over time as skin adapts. Some degree of flaking is a sign that the product is working. When using products that contain lactic acid, it’s important to avoid contact with the eyes since it’s an eye irritant. There’s no evidence that lactic acid is toxic to organs or that it increases the risk of cancer.
All in all, lactic acid is an effective moisturizer and keratolytic that can improve skin texture and lighten fine lines, wrinkles and pigmentation due to sun exposure. It also appears to be safe in the amount found in cosmetic and skin care products, although it can cause skin irritation and redness in some people. This usually improves over time. Lactic acid is naturally produced by the body and has a long history of being used in foods and skin products. That provides some level of assurance of its safety.