Crucial Role of pH in Cosmetic and Personal Care Formulation
In cosmetic and personal care products, pH is a crucial factor for maintaining the health and balance of the skin, as it directly influences the effectiveness of active ingredients, the stability of formulations (such as emulsions and preservatives), and the sensory qualities of the product. By precisely adjusting the pH, skin irritation can be minimized, and both the efficacy and shelf life of the product can be optimized.
pH is a critical parameter in cosmetic and personal care formulations, carefully considered from product development through to the evaluation of its effects on the skin. The skin’s surface pH is regarded as a key indicator of skin health. In this article, we will explore the impact of pH in cosmetic products in depth.
The pH of Cosmetic and Personal Care Products and Its Effects on Skin Health and Balance
Studies have shown that the skin’s pH can vary significantly depending on factors such as gender, age, and body area. Typically, the average pH of female skin is slightly higher—around 4.9—while in males, it is approximately 4.7. Newborns, on the other hand, generally have a higher skin pH, averaging around 6.5.
As mentioned earlier, different parts of the body have varying pH levels, and it is widely accepted that the use of cosmetic products can significantly impact skin pH. For example, research indicates a direct relationship between the pH of a body cleanser and its effect on the skin’s surface characteristics.
In acne-prone young adults, washing the face with an alkaline cleanser has been shown to trigger a stronger inflammatory response compared to using an acidic cleanser. Conversely, frequent washing with a mildly acidic cleanser—around pH 5.5, which is close to the natural pH of adult skin—can slightly increase the skin’s surface equilibrium pH. However, this change is significantly smaller than that caused by alkaline soaps.
Read more: The Importance of pH in Laundry Detergents | Five Key Roles
The Role of pH in Cosmetic Emulsions
Maintaining emulsion stability is a primary goal for formulators of cosmetic and personal care products. However, the importance of pH—and its role in creating optimal conditions for forming and sustaining a stable emulsion over time—is often underestimated. Studies have shown that most common soaps and shampoos have pH levels outside the natural range of skin and hair. Soaps typically have a pH between 9 and 10, while shampoos range from 6 to 7.
The Effect of pH on the Microbiological Stability of Cosmetic and Personal Care Products
Many preservatives used in cosmetic and personal care products are sensitive to pH. The pH of a formulation can significantly affect the efficacy of these preservatives. Some preservatives undergo pH-dependent degradation, while others—although seemingly stable—may become less effective within certain pH ranges. For example, sorbic acid and benzoic acid are more effective only within specific acidic pH levels. Similarly, parabens tend to lose effectiveness in alkaline formulations due to increased dissociation. In contrast, preservative boosters such as 1,2-diols perform better at lower pH values.
A lower pH environment also creates conditions that are less favorable for bacterial growth. Generally, microbial growth is optimal within a pH range of 6 to 8; outside this range, the growth rate decreases significantly. Most bacteria, including Escherichia coli (E. coli) and Staphylococcus species, do not thrive well in acidic conditions.
pH in Cosmetic and Personal Care Products and Its Effect on Viscosity
A shampoo must have sufficient viscosity (thickness) to remain in the hand before use, but it should become less viscous during application to spread easily over the hair and scalp. Several methods can increase a shampoo’s viscosity. In many surfactant systems, adding electrolytes such as sodium chloride helps increase viscosity.
However, in many cases, simply adding salt is not sufficient. pH can also influence the shape and size of micelles. In amphoteric surfactants such as cocamidopropyl betaine—one of the most common secondary amphoteric surfactants used in shampoo formulations—these molecules acquire a positive charge under acidic conditions and behave like cationic surfactants, typically resulting in an increase in viscosity.
Effect on Efficacy and Performance
For organic acids such as lactic acid, epidermal penetration increases at lower pH levels. The stability of active ingredients is also influenced by pH. For example, ascorbic acid (vitamin C) is more stable at pH values below 3.5 due to its pH sensitivity. Alpha hydroxy acids (AHAs) are most effective as skin-rejuvenating agents at very low pH levels, whereas depilatory agents perform best near pH 12. Additionally, pH-sensitive hydrogel micromolecules in cosmetic formulations can serve as efficient carriers for delivering active ingredients such as adenosine and niacinamide.
In addition, a product’s performance and sensory properties are closely linked to its pH. A significant portion of the interaction between surfactants and conditioning agents in shampoos occurs within the first fractions of a millimeter on the hair surface. Conditioning or two-in-one shampoos deposit conditioning agents onto the hair shaft, which neutralize surface charges, reduce friction between hair strands, and make the hair easier to comb and manage.
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Conclusion
Acidity and pH are critical and decisive factors in cosmetic formulations. The pH level of a formula determines the behavior of its ingredients, as well as the stability and efficacy of the final product. In fact, the influence of pH is extensive and fundamental, making precise pH control essential for proper formulation and optimal product performance.