Lactic Acid
Also known as: 2-Hydroxypropanoic acid, AHA
Description
Lactic acid is an alpha hydroxy acid (AHA) with a larger molecular weight (90.08 Da) than glycolic acid (76.03 Da), resulting in slower, more even penetration and generally better tolerability. Beyond its exfoliating properties, lactic acid uniquely functions as a humectant and stimulates ceramide synthesis in the stratum corneum. It is a component of the skin's natural moisturizing factor (NMF) and promotes epidermal turnover, improves skin texture, reduces hyperpigmentation, and strengthens the barrier.
Mechanism of Action
Lactic acid decreases corneocyte cohesion by disrupting ionic bonds between cells in the lower stratum corneum, promoting desquamation. It inhibits tyrosinase activity, contributing to its depigmenting effect. Lactic acid stimulates the production of ceramides (particularly ceramide 1 linoleate) in the epidermis, enhancing barrier function. At pH 3.5–4.0, it also exhibits humectant properties by attracting and retaining water in the stratum corneum. At higher concentrations, it increases dermal glycosaminoglycan and collagen synthesis.
Indications
- Keratosis pilaris
- Mild to moderate acne
- Post-inflammatory hyperpigmentation
- Melasma
- Photoaging / fine lines
- Xerosis / dry rough skin
- Ichthyosis vulgaris
- Uneven skin texture
Available Concentrations
Side Effects
- Mild stinging or burning on application
- Erythema
- Dryness and peeling
- Increased photosensitivity
- Irritant contact dermatitis at higher concentrations
Contraindications
- Known hypersensitivity to AHAs
- Active herpes simplex lesions (for peels)
- Open wounds or severely compromised skin
- Use with caution alongside retinoids or other exfoliants
Pregnancy Category
Generally considered safe at low OTC concentrations (≤10%); professional peels not recommended