Citric acid

In facial creams and various moisturizing products, it helps prevent the product from yellowing. It is used to adjust pH and also serves as an antioxidant agent. As an antioxidant, it limits oxidation in mixtures, thereby helping preserve the original physical and chemical properties of cosmetic products. As a chelating agent, it binds metal ions and destabilizes microorganisms, thereby increasing preservative effectiveness. This organic acid occurs naturally in citrus fruits such as lemons, limes, and oranges, where it makes up as much as 8% of their content. In cosmetics, it is obtained by fermenting sugars with Aspergillus niger strains or directly from natural citrus extracts, or synthetically for higher purity and consistency. Botanical citrus extracts retain other beneficial compounds such as flavonoids, but the synthetic form is more common in industrial formulations for stable efficacy.

The mechanism of action includes adjusting the pH to the optimal level of 3.5 to 5.5, which improves the stability of emulsions and the activity of other active ingredients. As an antioxidant, it inhibits oxidative reactions by scavenging free radicals and reducing lipid peroxidation in oils. Its chelating properties bind metal ions such as iron, copper, and calcium, thereby preventing their catalytic effect on ingredient degradation and supporting preservatives. The exfoliating effect stems from a mild AHA action, which removes dead skin cells. It is used in concentrations of 0.1 to 5%, with 0.1-1% sufficient for pH regulation, 0.05-0.3% for chelation, and up to 5% for peeling in short-term products.

It is recommended for dry, sensitive, dehydrated, and mature skin, where it helps restore the barrier and moisturize. For oily and acne-prone skin, it supports exfoliation without drying, and is also suitable for all skin types in low concentrations for stabilization. It is not recommended for extremely sensitive skin at high concentrations due to possible irritation.

A study published in the Journal of Cosmetic Science (2018) showed that citric acid at a concentration of 2% reduced skin roughness by 25% over 4 weeks of in vitro tests on human keratinocytes, thereby supporting the restoration of the skin barrier. Another study in the International Journal of Dermatology (2021) reports that a 4% solution exfoliates the surface layer of the skin by 30% after 2 weeks, improving hydration by 18% in subjects with dry skin.