There are two main categories of chemical exfoliants: alpha hydroxy acids (AHA) and beta hydroxy acids (BHA). AHA include some of the most commonly recognized ingredients; including glycolic acid, which is derived from sugarcane, and lactic acid, which is derived from milk. Other AHA ingredients that have become noteworthy are mandelic acid, which is derived from almonds; malic acid, which is derived from apples; and azelaic acid, which is derived from sunflower seeds. The range of AHAs continue with passionflower and lemon as a natural fruit source of citric and tartaric acid. BHAs include salicylic acid. The difference between AHAs and BHAs is their solubility. AHAs are water-soluble and their primary action lies in their keratolytic ability as they weaken bonds that hold dead skin cells together. When these bonds are weakened, the dead cells can be shed from the surface of the skin, resulting in skin that appears fresher, smoother, and younger. BHAs are oil-soluble and often capable of slipping through the natural skin lipids, but most importantly, solubilizing sebum and congestion in the pores, making it ideal for use on oily, congested, and acne-prone skin.

The benefits of safe and regular use of AHAs and BHAs go beyond the immediate sensation of smoothness left behind after their removal. Many AHAs function as intermediates in several key metabolic pathways. Due to biochemical conversion of acids that takes place upon their application and various chemical reactions with numerous skin molecules, they are also capable of producing many other skin-beneficial processes, such as generation of cellular energy, moisturization, and synthesis of glycosaminoglycans and collagens, which in turn improves elasticity.

AHA SOURCES AND BENEFITS

Glycolic acid is the most powerful and aggressive alpha hydroxy acid. This sugar cane-derived fruit acid seems to be the go-to ingredient by skin care professionals and consumers. Its popularity stems from its ability to penetrate quickly and efficiently – due to its small molecular size – breaking up the lipid and protein bonds between the cells and speeding up their exfoliation and turnover rate. It is effective for treating fine lines, acne, blackheads, dullness, and oiliness.

The second most common AHA is lactic acid. Lactic acid, works more on the surface due to larger molecule structure, so it has a gentler approach on the skin than glycolic acid. It reduces surface cell buildup while infusing plumping moisture into the skin’s surface. Those that suffer from dry skin should look to lactic acid as their AHA solution because it is not only more gentle than glycolic, but also has the ability to soften the skin and provide it with an efficient exfoliation. Lactic acid also works to minimize fine lines and wrinkles and restore extraordinary smoothness to skin.

Mandelic acid is a larger, almond-derived AHA with purifying and brightening properties and is ideal for sensitive skin and those with pigmentation issues. It works to speed up cell turnover, sloughing dead cells and enhancing the skin’s overall complexion and glow. Mandelic acid is comprised of a large-form molecule that allows for slow and even penetration, making it gentle enough for sensitive, rosacea-prone, or mature skin, as it promotes rejuvenation without skin irritation or erythema. In addition, it is quite beneficial in treating the skin pre- and post-laser peeling or surgery.

Azelaic acid is a potent, yet gentle, multifunctional acid that is commonly found in wheat, rye, and barley, but can also be derived from sunflowers. It works by breaking down cell buildup and puts up a fight against acne-causing microbes, in turn, helping to clear up congestion and breakouts. Azelaic acid is often used for those in need of brightening acne and inflammation-induced pigmentation. This alpha hydroxy acid is great for those with rosacea-prone skin because it helps reduce inflammatory lesions, minimize redness, and calm papular and pustular breakouts.

BHA SOURCES AND BENEFITS

Salicylic acid, a keratolytic BHA that is derived from willow bark and can penetrate into the pore lining, reduces sebum buildup and exfoliates inside the pore, as well as on the surface of skin. It is an effective antimicrobial and anti-irritant, reducing the occurrence of breakouts and keeping the skin calm while resurfacing. Salicylic acid works quickly to lift off dead, unwanted pigmented cells while reducing oil and cell buildup in the pore, which helps prevent inflammatory comedones and breakouts.

REGULAR EXFOLIATION

There is no other comparable ingredient that works likes a chemical exfoliant does when it comes to its ability to exfoliate and maintain the health of the skin. The skin’s desquamation process slows with age. This slowing can also be a result of exposure to environmental aggressors, such as pollution, ultraviolet rays, climate, and environmental allergens. Unlike a mechanical exfoliant that uses a granular mechanism or beadlets to polish the skin or enzymes that have a proteolytic effect on the surface cells, chemical exfoliants work by loosening the glue-like substances that hold the cells together, which, in turn, help penetrate the skin to loosen clingy bonds and assist in the shedding of the dull, damaged layer on the skin’s surface. Exfoliation is one of the most important components of professional skin care treatments and homecare regimens. A regular exfoliation regimen can help address and resolve certain skin concerns and maintain healthy skin. People need to rid their stratum corneum of dry skin cells that sit on the surface layer and accumulate, as they can further damage the barrier, cause irritation, aggravate acne, clog pores, increase the appearance of wrinkles, and give the skin an overall dry, dull appearance.

A visit to a plastic surgeon or skin care professional is still the best option for receiving a chemical peel. However, today, products containing chemical exfoliants are widely used throughout the industry in various measures, depending on the market in which they are sold. Both AHAs and BHAs are formulated in almost everything, in a variety of forms, from cleansers, toners, and moisturizers to weekly exfoliants, serums, and body lotions. Using skin care products that include safe levels of AHAs or a BHA is a great way to incorporate chemical exfoliation into a daily skin care routine, as they can address a multitude of skin issues and elongate the results from professional treatments. Most often, professionals will recommend multiple AHA-containing products for home use. For example, a mild exfoliating gel cleanser can help sweep away pore-clogging impurities, dead skin cells, and environmental contaminants on a daily basis, in turn leaving the skin more refined, clean, and smooth. Also, applying a mild glycolic acid serum or blended AHA serum under a day or night cream is a nice option. With this type of application, leave it on the skin and it will work to dissolve the dry skin cells, revealing a brighter, smoother, more refined complexion. For most skin types, clients can incorporate both of these product categories into their homecare routine at least every other day so they are getting effective exfoliation while giving their skin a break. Dependent on the condition of the skin, clients can then combine chemical exfoliation with a mechanical exfoliation, like a mild facial scrub, once or twice a week.

COMBINING ACIDS

Since various AHAs and BHAs work differently, combining selected acids can be very beneficial, as combinations of acids can improve more than one issue the client wants to address. Phytic acid, for example, which is naturally occurring in rice, although not a “true AHA” and not very capable of producing a deep exfoliating effect on its own, is actually considered to be an excellent antioxidant. Phytic acid also has a potent anti-tyrosinase effect and binds out iron, providing a strong “chelating” effect in the formula. All of these additional benefits make phytic acid a perfect addition to any combination of fruit acids, AHAs, and BHAs in the formulation, as its properties enhance an antioxidant, brightening, and soothing effect on the skin, all of which is much needed during, and after, skin exfoliation. It is normal to induce some degree of inflammation during exfoliation, which, in turn, activates free radical production that can not only result in prolonged discomfort, but can also cause potential hyperpigmentation. Since phytic acid best penetrates the skin when combined with other AHAs, its free radical-scavenging potential can stop the vicious circle of inflammation and vasodilatation, resulting in prolonged redness.

For example, a combination of lactic, phytic, and mandelic acids can help improve skin texture and treat signs of aging, uneven pigmentation, and past damage. This type of peel solution essentially targets three points at the same time: skin refining, brightening, and age-defying. A peel solution that is formulated with glycolic, mandelic, azelaic, and salicylic acids can radically lift dark spots and pigment, while purifying congested pores and softening past scarring and rough, uneven texture. Another example is an extra strength retexturizing multi-acid solution that combines synergistic action of glycolic, lactic, and salicylic acids for minimized signs of advanced sun damage, deep wrinkle correction, and overall rejuvenation. A solution of the combination can also reduce excess sebum and dead cell buildup, helping to clear breakouts and pore congestion.

It is not uncommon to see a blend of fruit acids naturally contained within various botanical extracts, such as bilberry, sugar cane, sugar maple, orange, and lemon, incorporated in both retail and professional exfoliating products. These extracts contain several naturally AHAs and the extract is produced by taking several species of plants and running them through an extraction process, which reduces color and odor and concentrates the active principles. The extracts are blended at varying percentages, with some being more dominant, while others may only be present in a miniscule range. Although they may not be as potent as pure glycolic or tartaric acids, blending them with other more potent acids has been shown to promote smoother and younger-looking skin by increasing the rate of cell renewal.

APPLICATION

What separates a chemical exfoliants’ performance is the level of training and experience of the professional applying them, the acid percentage, the client’s pH, and how buffered or neutralized the solution is within which they are included. The acid percentage can tell professionals the product’s strength, while the pH can tell them how deep it travels and its exfoliating potential. The pH scale ranges from 0 to 14, with 0 being the most acidic and 14 being the most alkaline. Distilled water is considered neutral with a pH of 7, so it is neither an acid nor a base. The pH of skin ideally should be slightly acid and around a level of 5.5. Since AHAs and BHAs exfoliate skin due to their acidic component, pH is critical to their performance.

Most AHAs are easy to apply, but not necessarily as easy to neutralize.1 Unlike more aggressive peels performed by the medical professionals, such as trichloroacetic (TCA) or carbolic acid (phenol) peels, AHAs do not auto-neutralize by combination with proteins. TCA, for example, combines with the dermal and epidermal proteins, producing a so-called “frosting” due to a modification of the inner structure of the proteins. The frosting means that TCA has made its effect and is neutralized. AHAs, on the other hand, will not produce frosting and should be neutralized when they reach the right depth in the skin – for example, after erythema becomes visible and before any frosting starts to appear. This may not be the best method of determining the right time to neutralize, so manufacturers’ or supplier’s instructions on the length of time the peel or exfoliant needs to stay on the skin becomes very important. The difficulty in using visible erythema as the guideline for acid neutralization or removal often comes from the subjectivity in determining the right moment for the neutralization, which is the reason why many AHA solutions are available in a “partially neutralized” form, which only needs to be rinsed off, but not neutralized with another product. Without external neutralization, many AHAs would continue its action and overpass the desired effect; if they neutralize too quickly, the desired effects of an AHA exfoliation might not be there.

If the acid peel or exfoliating solution is just rinsed with water, neutralization does not necessarily occur, but a dilution of the acid occurs instead. Most lower percentage and lower pH acids can be diluted to become harmless and do not need true neutralization, but the supplier should be able to confirm whether the acid peel mix has been partially neutralized or buffered or if it requires neutralization via an additional step and product.

The contact time between the skin and the acid or the length of time that the acid is left on the skin is very important for the clinical efficacy of any AHA peel.3 Generally speaking, the results will be more pronounced if the peel is left on the skin for five minutes versus one minute. In order to prevent the risk of “over-peeling” or “over-processing,” which can lead to post-peel problems, many peels can be “layered” instead. This technique involves applying and removing several layers of the peel solution (usually up to five) while leaving the peel solution on for a shorter period of time.

FDA RECOMMENDATIONS

It is important to note that the FDA has a very specific view on how AHAs are utilized in both retail and professional skin care products. In 1997, the Cosmetic Ingredient Review (CIR) reviewed the safety of glycolic and lactic acids and their salts and simple esters. The panel concluded that in general consumer cosmetics, these ingredients were safe for use at levels up to 10 percent at pH 3.5 when formulated to avoid increasing sun sensitivity or when directions for its use include the daily use of sun protection. For professional products, the panel considered the compounds safe at up to 30 percent at pH 3.0 when designed for brief, discontinuous use, followed by thorough rinsing from the skin and when applied by a trained individual and when application is accompanied by directions for the daily use of sun protection. These recommendations stem from the FDA’s concerns relating to the safe use of AHAs in cosmetic products in regard to the safety of their long-term use, their effect on the maintenance of barrier integrity, their effects on absorption of other cosmetic ingredients, and their effects on skin’s responses to ultraviolet exposure.

Given the vast number of products on the market containing much higher percentage of acids and a much lower pH than what the FDA recommends, it is crucial to obtain as much information and training as possible from the manufacturer in order to ensure safe and effective use of acids, with both in homecare formulations and professional peels.

References

1. Deprez, P.: AHA’s y ácido fítico: eliminación del prob- lema de la neutralización. Salud Estética 2001;4:47–51.

2. Brody, H.J.: Chemical peelings and resurfacing. In Al- pha Hydroxy Acids. Mosby, 1997: pp. 90–99.

3. Prunieras, M.: Précis de cosmétologie dermatologique. In: Perméabilité aux Agents Externes. 2nd ed. Masson, 1990, pp. 8–11.

Ashley Stowers is a national educator and account executive for YG Laboratories and CelleClé Skincare. In addition to her role in sales, Stowers provides hands-on support in all aspects of education and product knowledge training, protocol development, and effective business merchandising. With over 15 years of experience in sales and education, holding positions as an aesthetics instructor and skin care therapist, Stowers possesses a very broad and unique understanding of the professional world and skin care industry.