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
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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.
The acid mantle is a thin layer that helps skin remain healthier and free of blemishes. P. acnes bacteria is the major cause of blemishes when it reacts with oil and dead skin cells. Acid-formulated products and acid-based peels are often used as a primary treatment in resolving acne concerns, but often, due to the misunderstanding of pH, products that are too aggressive are used, resulting in redness and irritation. If the skin’s acid mantle is disrupted negatively, the skin becomes vulnerable to damage and infection. Helping to keep clients’ skin at the correct pH stabilizes skin’s barrier function by preventing water loss from the inside, as well as blocking the penetration of pollution and irritants from the environment.
The optimum pH
So, what is the optimum pH for effective skin health? Each skin concern needs a slightly different adjustment to the pH of the formula used, as does each set of products used to treat it. Often, a skin care protocol will include a combination of a few products formulated at various pH levels to optimize results. When formulating anti-aging products, it is common to include in the protocol a few products that help to increase exfoliation of the skin to minimize fine lines and wrinkles, and to increase hydration. The skin cell turnover rate for a client age 16–20 is, on average, 14 days. For every year a person ages beyond 20, it increases by one day. At age 30, it takes an average of 24 days for cells to turn over and reveal younger, healthier skin. At age 40, it takes 34 days and, at 50, well over a month at 44 days, resulting in the need for acid-based products.
Three things need to be considered when using a product and determining its ideal pH.
- What is the skin concern you are treating?
- What is the desired result of the treatment? Do you want to only increase exfoliation, or for the skin to actually peel?
- How much time will this product remain on the skin? Is it an in-spa treatment or an at-home product?
In-spa vs. home care
Everyday home-care products can vary from acidic to alkaline formulations. Professional in-spa use products are usually more acidic and can be formulated as low as pH 2, although the esthetic standard is no lower than a pH 3. Home-care products often range from pH 4–6, depending on whether they are cleansers or treatments that will remain on the skin for a longer period of time. Glycolic acid is the most popular of the acids used in formulations because of its smaller molecular size and ability to penetrate. Often, formulations will include a combination of several different acids. A common favorite combination is glycolic and lactic. Salicylic is often used alone or in combination with glycolic for the treatment of acne.
Lower pH products are used in the treatment of hyperpigmentation to obtain visible results by helping to accelerate the exfoliation of pigmentation in the epidermal layer. Try formulations that add holistic and alternative actives to the acid base in order to help prevent—as well as resolve—the current skin concern. Favorites for hyperpigmentation are arbutin, bearberry and kojic acid. Vitamin C, zinc, CoQ10 and retinoic acid help restore metabolic rejuvenation to damaged skin for healthier, long-term results.
Although maintaining the skin’s acid mantle is critical to good skin health, you don’t want to use too many products that are acidic. In a medical practice, peels can easily be as low as pH 1.7 in a solution of 50–70%. These peels need to be in trained, professional hands only. For the esthetician, a peel solution that combines AHA ingredients with select actives should be around a pH 3.0 in a solution of 30%.
Performing these peels in a series of five or six is much more beneficial and leads to better results without the risk of hyperpigmentation. Formulators of products have a responsibility to carefully test and buffer each of their formulations, taking into consideration the area of the body on which the product will be used—legs and arms can handle lower pH products than the face—and what skin concern the product will address.
A better understanding
It is known today that a lower pH value in a skin care product—provided it is not too low and is used properly—is an absolute requirement for product activity with a correlation between pH, concentration and optimal activity. Anti-aging benefits can be irritating, so these benefits need to be customized for each client and balanced with irritation, as well as overall skin health and well-being. The professional skin care industry keeps learning just how effective skin care can be, and testing continues to determine optimum levels for actives and pH. Professionals must continue working to obtain a better understanding of how to use chemistry to recommend better formulations without negative effects.
Elaine Linker is the director of corporate communications and education for Christina Skincare USA and has more than 20 years of industry experience. As co-founder of DDF, Doctor’s Dermatologic Formula, Linker helped de-mystify the science around skin care by explaining each skin concern in an easy-to-remember way. She is a sought-after speaker, as well as a published writer.
- www.elmhurst.edu/~chm/vchembook/184ph.html (Accessed Jul 16, 2012)
- MH Schmid-Wendtner and HC Korting, The pH of the skin surface and its impact on the barrier function, Skin Pharmacol Physiol 19 6 296–302 Epub (Jul 19, 2006)
- 3. www.sebamed.com (Accessed Jul 16, 2012)
Editor’s note: To learn more about the basics of formulating professional skin care and cosmetic products, check out the book Beginning Cosmetic Chemistry, Third Edition (Alluredbooks, 2009) by Randy Schuller and Perry Romanowski. It can be purchased at www.Alluredbooks.com.