What is Citric Acid

Citric acid is a weak organic acid naturally present in citrus fruits, especially lemons and limes, but also in raspberries, currants, and other fruits. In cosmetics, it is primarily obtained by fermenting sugars using the fungus Aspergillus niger, an efficient biotechnological process that makes it accessible and plant-derived.

It is an alpha-hydroxy acid (AHA) like lactic acid or glycolic acid, but in cosmetics, its main role is not to exfoliate but to regulate the pH of formulas. It appears in almost all types of products, from serums to mouthwashes, as a formulation tool rather than a star active ingredient.

How it works in formulas and on the skin

Its main function is pH adjustment. Skin has a slightly acidic pH, between 4.5 and 5.5, and many active ingredients only work correctly within that range. Citric acid allows formulators to precisely adjust the final pH of the product, ensuring both the efficacy of the active ingredients and skin tolerance.

As an antioxidant, it protects the formula from oxidation, extending the product's shelf life alongside tocopherol and other natural preservatives. In low concentrations, it does not have significant exfoliating action, but in specific products, it can contribute to superficial renewal and a brightening effect.

In oral hygiene, it acts as a chelating agent, capturing metal ions that promote the formation of tartar and plaque, and contributes to pH balance in the oral cavity.

Properties and benefits

• pH regulator, ensures active ingredient efficacy and skin tolerance
• Mild antioxidant, stabilizes formulas rich in sensitive active ingredients
• Chelating agent, captures metal ions in formulas and in oral hygiene
• Gentle exfoliant in specific concentrations
• Superficial brightener with continuous use
• Compatible with all skin types at usual formulation concentrations
• Supportive preservative, extends product shelf life

Usage and integration into your routine

Citric acid appears in several products in the CUIDA-T catalog as a formulation ingredient: serums, solid shampoos, shower gels, mouthwashes. In most cases, its concentration is low, sufficient to adjust pH without noticeable exfoliating action.

It naturally combines with hyaluronic acidin moisturizing serums, where it stabilizes the optimal pH for its function, with vitamin Cwhose activity is closely dependent on acidic pH, and with tocopherolforming an antioxidant duo that protects the formula.

Interesting facts and trivia

Lemon isn't as acidic as it seems
Lemon juice has a pH of between 2 and 3, much lower than that of the skin. Applying it directly to the skin without diluting or formulating can irritate, alter the skin barrier, and cause photosensitivity. Citric acid in formulated cosmetics works at very different concentrations and pH levels, without this risk. Lemon on the face is an old wives' tale that modern formulation has left behind.

The Krebs cycle uses it constantly
Citric acid is not just cosmetic or food-related: it is a central molecule in cellular metabolism. The Krebs cycle, the process by which cells obtain energy, is named precisely because citric acid is the first compound formed in that cycle. It is in every cell of your body, working continuously.

From citrus to industrial fermentation
Until the early 20th century, citric acid was extracted directly from Sicilian lemons, which monopolized the world market. In 1917, biochemist James Currie discovered that the fungus Aspergillus niger could produce it by fermenting sugars on a large scale. Within a few years, the Italian lemon industry collapsed. Today, over 99% of the world's citric acid is produced by fermentation, not by fruit extraction.

The anti-hero of formulation
Citric acid rarely appears in a product's marketing. It doesn't have an evocative name, it doesn't sell serums or justify a premium price. But without it, many formulas would be ineffective or unstable. It's the ingredient that makes others work, the one no one mentions but everyone needs.

It appears in the INCI as: Citric Acid

Other active ingredients you might be interested in

Lactic acid: another AHA with more pronounced exfoliating action, a natural complement to citric acid in renewal routines.
Vitamin C: an antioxidant whose efficacy is closely dependent on the acidic pH that citric acid helps maintain.
Tocopherol: a complementary antioxidant that, together with citric acid, stabilizes and protects the formula.
Hyaluronic acid: a star humectant that works in the acidic pH range regulated by citric acid.