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How pH Affects the Formulation of a Product
By: Elaine Linker
Posted: September 28, 2012, from the October 2012 issue of Skin Inc. magazine.
There may be more confusion and misunderstanding about pH and how it affects a product’s efficacy than any other formulation criteria in the professional skin care industry. Most people still associate the percentage of an acid with its efficacy—a higher percentage acid being more effective and aggressive. In fact, it is actually the pH of an acid that is the major driver of the potency of a product. If you use peels in your skin care facility, understanding this chemistry is critical to selecting the correct peel solution for your clients.
To understand why the slightest difference in pH in a formulation can make a major change in how a skin care product interacts with the skin, it is necessary to have some basic understanding of chemistry. pH is the measure of the acidity and alkalinity of a solution. “Acid” and “basic” are two extremes that describe the chemical property. The pH number represents the relative relationship between the acid and alkaline mix. Mixing acids and bases can cancel out or neutralize their solutions. A solution that is neither acidic nor basic is neutral. The pH scale is logarithmic and ranges from 0–14, and the center of the scale—7.0—is neutral. How these logarithmic facts affect the formulation is key to understanding the potency of a product, particularly a peel solution.
Each whole pH value below 7 is 10 times more acidic than the next higher value. For example, a pH 4 is 10 times more acidic the a pH 5 and 100 times more acidic then than a pH 6. The same holds true for pH values above a 7 (alkaline), with each having the same exponential value.1
What this means for the formulation is that the slightest change in the pH of the formulation makes a significant difference in its strength and ability to react with the skin. Merely changing the pH in a formulation by one-tenth of a decimal point substantially increases this. All acids are driven by pH as their primary criteria in formulation. A 50% glycolic acid can be made as mild as water by adjusting the pH. Conversely, a 30% glycolic acid peel solution at a pH of 2–2.5 would be very potent. The same adjustments can be made to home-care products, and each of the products formulated with a slightly different pH will react with the skin in a totally different manner. As a skin care professional, the most important detail to consider is the pH of the product. Your treatment goals for each client will determine the strength of the product.
The acid mantle
A common range of the pH of skin is often between 5.4–5.9. Results based upon recent experiment ranges by MH Schmid and HC Korting suggest a more ideal range being from pH 4.0–4.9.2 Beauty products are formulated to be in the range of mild acidity, between 4.6 and 5, to help the skin look and feel its best, although anti-aging products may need to be formulated in the range of 3–3.5 for optimum results. The natural acid mantle helps skin resist environmental pathogens. As the largest organ in the body, the skin acts as a barrier to multiple kinds of pathogens that naturally exist in the environment.