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