Acid Breakdown

Exploring AHAs, BHAs, and PHAs in skincare


Hydrating acids, skin-clearing acids, exfoliating acids, acid peels – so many products and procedures make use of these magical chemical compounds to provide the best results. But what are they? What is the difference? Which one is best for sensitive skin? Aging skin? Acne-prone skin? The information online ranges from overwhelming to underwhelming. Here you will find enough information to speak confidently on acids as well as make the best decisions for your clients!


The most widely talked about acid group are the AHAs (alpha-hydroxy acids). Alpha hydroxy acids are known as “wounding agents” or fruit acids. They work by exfoliating the stratum corneum which then activates hyaluronic acid and the syntheses of glycosaminoglycans as well as collagen to improve elasticity and hydration. Alpha hydroxy acids are used to treat photodamage, hyperpigmentation, eczema, acne, actinic keratosis, in addition to fine lines and wrinkles. There are six key alpha hydroxy acids: glycolic, lactic, malic, tartaric, citric, and pyruvic.

Glycolic acid is the most widely used AHA, however, it is considered the most aggressive but the most penetrative due to its small molecular size. It is made from sugarcane but can be synthesized in a lab. It works by breaking apart the desmosome bond of the hardened keratinocytes to slough away dead skin, which then increases its water-binding ability to provide more moisture to the skin.

Lactic acid is a gentler exfoliator made from sour milk but is also found in muscle tissue. It has a larger molecular structure, so it works on just the surface level of the epidermis. It is used as an exfoliant but also as a preservative and moisturizer. Levels of 5 to 12 percent are known to cause an improvement in hyperpigmentation, fine lines and wrinkles, as well as improved moisture levels within the skin.

Malic acid is the third smallest molecular structure within the alpha hydroxy acid family. It can be quite irritating and difficult to work with, so it is mainly used in conjunction with other acids. Tartaric, citric, and pyruvic acids also fall into the category of “difficult to work with” but with a larger molecular size.

Two alpha-hydroxy acids are gaining in popularity and are much easier to work with as well as being much gentler to the skin: mandelic and azelaic acid. Mandelic acid is a gentle exfoliating acid that is made from bitter almonds. It is a large form molecule that allows for a much more even and slow penetration rate. It is known for its purifying and brightening effects and is used per or post-laser peeling or surgery.

It is best to mention that this acid is gentle enough for skin with rosacea, that is sensitized, or has erythema. Azelaic acid is also a gentler acid that comes from sunflowers, wheat, rye, or barley. It reduces inflammatory lesions, minimizes redness, has an antimicrobial element, as well as the ability to calm popular or pustular breakouts. Azelaic acid also can brighten macules left behind from acne or inflammation.

“Two alpha-hydroxy acids are gaining in popularity and are much easier to work with as well as being much gentler to the skin: mandelic and azelaic acid.”

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The next classification of acids is BHAs (beta hydroxy acids). These also refine texture by reducing epidermal thickness through surface exfoliation. The most commonly known BHA is salicylic acid. Salicylic acid is made from willow bark but has some components found in aspirin. It is lipid-soluble so it can penetrate deeper into the pore to reduce follicular blockage and exfoliates cellular build-up (think blackheads). Salicylic acid has antimicrobial and antiseptic properties which make it great for acne! It is also safer to use on darker skin types for hyperpigmentation issues than the more aggressive solutions.


The last grouping of acids is PHAs (polyhydroxy acids). These are being hailed as the “new generation of AHAs”. The three most common are gluconolactone, galactose, and lactobionic. These acids exfoliate similar to alpha-hydroxy acids but with antioxidant properties to stop free radicals. Their molecular size is larger which means the penetrative depth is surface level as well as minimal irritation. They also have humectant and moisturizing properties due to their water-binding properties. Another honorable mention about PHAs is that they are shown to boost the benefits of other treatments: retinoids, skin bleaching, laser procedures, and microdermabrasion.

As with any treatment, be sure to check on allergies or contraindications for the type of acid you are using or suggesting. Be sure to do a patch test 24 hours before the client’s treatment and always have an acid neutralizer on hand. Hopefully, you consider yourself more comfortable with the types of acids used for facial treatments and can recommend with confidence!