What is the purpose of a pH regulator in cosmetics?

The pH, or potential of hydrogen, is an indicator of the acidity or alkalinity of a solution or surface. It is expressed on a scale ranging from 0 to 14 and represents the activity of hydrogen ions H+, which can be compared to their concentration. In an aqueous environment at 25°C, considered a neutral medium, a solution with a pH equal to 7, or between 6.6 and 7.3, is said to be neutral. If its pH is less than 7, it is classified as acidic, and if it is greater than 7, it is said to be basic. In cosmetics, the concept of pH is important because a product that is too acidic or too alkaline can strongly irritate the skin.

The skin's pH is slightly acidic and typically ranges between 4.7 and 5.75.

The natural acidity of the skin is explained by the presence on its surface of an acid mantle, the hydrolipidic film. This is a key factor in the homeostasis of the skin barrier, its integrity, and its antimicrobial defense capabilities, primarily composed of sebum and sweat. Furthermore, ceramides, essential lipids of the stratum corneum, are synthesized at an acidic pH by pH-dependent enzymes. The dysregulation of skin pH can lead to several discomforts, such as the weakening of the barrier function, destabilization of the skin microbiota, or the appearance of imperfections.

In order to respect the physiology of the skin and its natural acidity, cosmetic care products are generally formulated at pH levels ranging from 4.5 to 7, depending on their type and function. Indeed, serums, lotions, and face creams often have a pH close to 4.5, while rinse-off cleansing products can have a pH up to 7. In order for the care products to adhere to these pH ranges, it is necessary for formulators to use pH regulators, also known as pH adjusters.

The primary function of pH regulators is to adjust the pH of a solution in order to achieve an acid-base balance that respects the skin.

This primary function of pH regulators allows them to fulfill various roles.

• Regulators contribute to making cosmetics stable.

  pH variations can impact the active ingredients in cosmetic formulas, leading to their degradation, oxidation, or precipitation. pH regulators help stabilize skincare products, ensuring they maintain their properties and effectiveness throughout their lifespan.

• pH regulators play a role in the safety of skincare products.

  To prevent irritations and other undesirable skin reactions, it is crucial that the pH of topically applied products is compatible with the skin. pH regulators ensure that cosmetics remain within a safe pH range for the skin.

• pH regulators enhance the effectiveness of active ingredients.

  Some cosmetic ingredients, such as fruit acids (AHA) or vitamin C, are only effective within a specific pH range. Moreover, certain active ingredients are only compatible with each other at a precise pH, where they can interact without altering their respective properties. Therefore, the role of pH regulators is to ensure an environment where each active ingredient can fulfill its function, while acting in synergy with the others.

• pH regulators help prevent microbial contamination.

  The pH plays a significant role in the action of preservatives. Indeed, their effectiveness can be hindered by a pH that is too high or too low, which can increase the risk of bacterial or fungal proliferation in a product. pH regulators thus help maintain an environment where preservatives can be fully effective.

• pH regulators influence the organoleptic characteristics of skincare products.

  A pH variation in a skincare product can macroscopically manifest as a change in its texture, viscosity, color, or odor. By keeping the pH constant, pH regulators help to maintain the appearance and feel of cosmetics.

The pH regulators that can be found in cosmetic products are predominantly weak acids and bases, meaning they do not fully dissociate in water. Among them, we can mention acetic, adipic, ascorbic, boric, citric, fumaric, glycolic, lactic, malic, and uric acids, ammonium, calcium, magnesium, potassium, and sodium hydroxides, ammonium, calcium, potassium, and sodium phosphates, and alkanolamines, such as ethanolamine, triethanolamine, and tromethamine. At Typology, we particularly use citric acid (INCI: Citric Acid), lactic acid (INCI: Lactic Acid), sodium citrate (INCI: Sodium Citrate), and sodium hydroxide (INCI: Sodium Hydroxide) to regulate the pH of our skincare products.

• DRAELOS Z. K. Cosmetics: An overview. Current Problems in Dermatology (1995).

• BRAUN-FALCO O. & al. The effect of detergents on skin pH and its consequences. Clinics in Dermatology (1996).

• YOSIPOVITCH G. & al. Skin pH : From basic science to basic skin care. Acta Dermato-Venereologica (2013).