Your batch failed because of the pH. Here’s why (and how to avoid it by considering your cosmetic pH correctors).
An incorrect pH can destroy the preservative in your cosmetics. Master the art of pH correctors and prevent your batch from failing with this definitive guide for formulators.
The Critical Importance of pH in Cosmetic Formulations
The pH of a cosmetic should never alter the skin’s pH or the acid barrier that protects it.
The vast majority of cosmetics (mainly emulsified) have values between 4.9 and 5.9, with 5.5 as the core value. Skin changes occur outside this range.
Very alkaline values, such as those found in hygiene products, can over-dry the skin or produce the opposite effect if they are too acidic.
Skin changes when the pH value is outside this range result from a dysfunction in the skin’s defense system, leading to the appearance of acne, dermatitis, irritations, or infections. When alkaline active ingredients or agents are used, the skin has a series of components present in its protective acid mantle known as buffer substances. They are responsible for neutralizing the pH, stabilizing the skin’s own acidic environment. This process is called alkaline neutralization capacity.
The pH influences the concentration of ionized and solubilized active ingredients with cosmetic activity. It is important to know the most stable pH values for an active ingredient, as this value influences the degree of cosmetic activity and the requirements for the penetration route. The stability value is the pH value of the active ingredient under normal conditions.
What are pH correctors?
Cosmetic pH regulators are weak acids or bases designed to adjust and maintain the pH level of cosmetic products within a limited range. Some common examples of cosmetic pH regulators include citric acid or sodium hydroxide (caustic soda). These ingredients are carefully selected based on the specific requirements of the formula and the type of product being formulated.
Functions of pH correctors
- Maintaining Optimal pH: pH regulators in cosmetics help maintain the correct pH. This is important for the product’s function and compatibility with the skin. The optimal pH can vary depending on the type of product and how it is applied. For skin care, a slightly acidic pH, around 5.5, is ideal. This helps maintain the health of the skin barrier and reduce discomfort.
- Formula Stability: Changes in pH can affect the imbalance of active ingredients and the overall mixture. pH regulators help alter the chemical order of cosmetic products. This prevents pH-sensitive ingredients from degrading and increases the cosmetic’s shelf life.
- Skin Compatibility: An unsuitable pH can cause discomfort and skin sensitivity. To reduce the risk of adverse reactions and ensure a comfortable experience, the pH should be adjusted. This should be the skin’s natural pH.
- Improves the effectiveness of active ingredients: pH regulators can enhance the effectiveness of active ingredients in cosmetic formulas. Some active ingredients require a specific pH to be absorbed by the skin or to perform their function properly.
- Adjusting texture and skin feel: pH can influence the texture and feel of a cosmetic product. pH regulators can help achieve the desired consistency and improve the user experience by providing a smooth and pleasant application.
How to adjust the pH in cosmetics?
Common Acidifiers in Cosmetics:
- Citric Acid: Widely used, good profile, mild chelating agent.
- Lactic Acid: AHA, also moisturizing.
- Other Organic Acids (Glycolic, Malic – if also used for adjustment).
- Acid Phosphates (Buffer).
Common Alkalizers in Cosmetics:
- Sodium Hydroxide (NaOH): Strong base, very effective, requires careful handling and low concentration.
- Triethanolamine (TEA): Common in emulsions, may have concerns (nitrosamines). Cosmetic TEA.
- Arginine: Amino acid, more “natural” or gentler option. Arginine pH.
- Aminomethyl Propanol (AMP).
- Potassium Hydroxide (KOH).
- Alkaline Phosphates (Buffer).
What should be considered when formulating?
Since the substances the body produces constantly change, skin pH also changes. However, it’s not the only factor at play: other factors also influence this, such as age, skin type, and gender.
Furthermore, when formulating a cosmetic, it’s essential to consider the area of the body where it will be applied, as each area secretes different substances. Generally speaking, the average skin pH is 4.7, but it’s not uniform across the body. For example, the eye contour has a pH between 7 and 7.5, so cosmetics designed for this area must be formulated with a basic pH.
Why is pH so important in cosmetic formulation?
Sensoriality
pH directly affects the stability of cosmetics, influencing viscosity, color, and texture—all aspects that determine the sensory experience of a cosmetic. Furthermore, an inadequate pH can promote bacterial growth, even compromising its safety.
Cosmetic Efficacy
Some active ingredients only work within a specific pH range. Therefore, we can say that an inadequate pH can degrade some ingredients, reducing their shelf life.
Safety
The pH of the skin varies depending on the area of the body; when formulating a cosmetic, we must ensure that this balance is respected. Products with a highly acidic or alkaline pH can disrupt the skin barrier.
Surfactants and pH
Anionic surfactants, such as sulfates and soaps, work best at neutral or alkaline pH, as in acidic environments they can lose charge and reduce their detergent capacity.
Cationic surfactants, found in conditioners, are most effective at acidic pH, where they maintain their positive charge and improve adhesion to the hair. As a result, hair is softer, more manageable, and less prone to frizz. Thanks to this complementary action, shampoo, with anionic surfactants, deeply cleanses, while conditioner, with cationic surfactants, restores softness and reduces friction.
To optimize the formula, cationic surfactants are strategically combined with anionic surfactants, as their properties complement each other. Furthermore, non-ionic surfactants are stable over a wide pH range but can degrade under extreme conditions. Finally, amphoteric surfactants, such as betaines, change their charge depending on the pH, allowing them to adapt and add softness to formulas.
While pH greatly influences the behavior of surfactants, we must not forget that it affects the entire cosmetic formula. From preservatives to emollients, each ingredient has its own stability range and, therefore, pH.
Does pH affect cosmetic preservation?
One of the potential effects of an inadequate pH range is microbial growth. For a preservative to be effective, it must be stable throughout its shelf life and able to withstand different pH conditions.
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