What are the benefits of lactic acid for the skin?

Lactic acid is also credited with the ability to delay the signs of skin aging. Indeed, studies in vitro have demonstrated that this molecule can stimulate collagen production by fibroblasts. As a reminder, collagen is a dermal protein that contributes to the skin’s suppleness and firmness. This potentially tightening effect of lactic acid is accompanied by antioxidant activity, which allows it to neutralize free radicals before they attack cellular components. Generated during energy metabolism, as well as following exposure to UV radiation, pollution, and tobacco, these radicals are among the main contributors to accelerated skin aging.

Coupled with its ability to stimulate cellular renewal, these various mechanisms explain why lactic acid is commonly used in professional peels to reduce the appearance of wrinkles.

Lactic acid is also interesting for evening out skin tone. Like other alpha hydroxy acids (AHAs), it can inhibit the activity of tyrosinase, an enzyme involved in melanogenesis, the process of melanin production. More precisely, tyrosinase is responsible for converting tyrosine, an amino acid, into melanin. A study on mouse melanoma cells showed that tyrosinase inhibition by lactic acid was dose-dependent and comparable to that of glycolic acid.

Moreover, the exfoliating action of lactic acid also helps diminish pigmented spots. Indeed, by promoting epidermal desquamation, this compound gradually disperses melanin clusters located in the basal layer. This process partly relies on the chelation of calcium ions, which weakens the junctions between corneocytes and reduces their adhesion, thus facilitating cell turnover. The combination of these two mechanisms – inhibition of melanogenesis and acceleration of epidermal renewal – explains why lactic acid is recognized for its efficacy in treating pigment irregularities and brown spots.

Lactic acid also plays an interesting role as an antibacterial agent. Studies have shown that at a concentration as low as 0.5%, it can completely inhibit the growth of pathogens such as Salmonella enteritidis, Escherichia coli or even Listeria monocytogenes. Its mechanism of action primarily relies on a profound alteration of the bacterial membrane: by penetrating into the periplasmic space via the channels of the outer membrane, lactic acid interacts with lipopolysaccharides and phosphate groups in the membrane, altering their charges and weakening the interactions that sustain its stability. This disruption promotes the release of essential components, such as lipopolysaccharides and glycerophospholipids, resulting in a loss of membrane integrity. Consequently, intracellular contents gradually leak out, causing sublethal damage and leading to the complete inhibition of bacterial growth.

Lactic acid is also endowed with anti-inflammatory and immunomodulatory effects which explain its soothing role. At high concentrations and in an acidic environment, it reduces the production of pro-inflammatory cytokines such as TNF-α and IL-1β by macrophages and monocytes. Several studies have shown that it can interfere with the energy metabolism of monocytes by inhibiting their glycolysis, thereby limiting their differentiation into dendritic cells and reducing T lymphocyte activation. It has also been demonstrated that lactic acid delays the expression of LPS-activated genes, notably those encoding the chemokines CCL2 and CCL7. This mechanism is linked to an attenuation of protein kinase B (PKB) phosphorylation and a decrease in IκBα degradation, which reduces the activation of the transcription factor NF-κB, a key player in inflammation.

When applied to the skin, these anti-inflammatory effects of lactic acid could help soothe redness and skin hypersensitivity. By limiting the inflammatory cascade, it may be beneficial for skin prone to inflammatory dermatoses, such as eczema, rosacea or inflammatory acne.

The exfoliating, antibacterial, and anti-inflammatory properties of lactic acid, as previously mentioned, can be particularly interesting in a context of blemish-prone skin. Indeed, a clinical study evaluated the efficacy of a series of 88% lactic acid peels in 25 phototypes III to VI patients with acne, 15 of whom also presented acne scarring. Three sessions spaced two weeks apart were conducted, with a three-month follow-up after the protocol. The results demonstrated a significant reduction in inflammatory lesions, as shown in the table below. Regarding scarring, improvement was moderate in 20% of patients, marked in 20%, and excellent in 60%. Despite some cases of transient post-inflammatory hyperpigmentation, this resolved within three months, resulting in a more even complexion.

Finally, lactic acid can support the skin repair process. Since the 1960s, it has been shown that lactate stimulates collagen synthesis by fibroblasts, particularly via the activation of prolyl hydroxylase, an enzyme essential for collagen fiber maturation. More recently, studies have confirmed that lactate acts as a genuine regeneration signal that promotes endothelial cell migration and the recruitment of vascular precursors. These effects converge to stimulate angiogenesis, i.e., the formation of new blood vessels, ensuring improved oxygen and nutrient supply to regenerating tissues.

Mouse models have also shown that lactate enhances extracellular matrix deposition and accelerates cutaneous wound repair. For example, one study in rats with wounds divided the animals into two groups: one received a daily application of a cream containing 50 mM sodium L-lactate, while the other received only the vehicle. The results showed that lactate application significantly promoted healing by increasing vascular density at the wound site and reducing lesion diameter over time. These data reinforce the idea that lactic acid and its derivatives can accelerate skin repair by supporting tissue regeneration and the formation of new blood vessels.