Decades ago, researchers discovered that topical hydroxy acids have a dramatic effect on the skin. Over time, science’s understanding of the benefits of these acids expanded dramatically, and today, hydroxy acids are some of the most powerful and popular ingredients in skincare.
Exfoliation is not a new concept to skincare users, but in recent years, educated shoppers have migrated from using harsh physical scrubs to relying on chemical exfoliation treatments to help remove dead skin and encourage fresh, healthy skin cells to come to the surface.
Drugstore scrubs were considered a staple in many skincare users' top shelves in the early aughts, but after a lawsuit popularized the idea that physical scrubs can do more harm than good, a shift occured in the larger discussion about at-home exfoliation. In 2016, two women filed a class-action lawsuit against St. Ives under the accusation that their widely loved Apricot Scrub actually could accelerate the aging process and encourage the development of fine lines because of its intensity and the micro-tears that its key ingredients could cause. Since then, many new physical exfoliants for the face have avoided walnuts, apricots, and other ingredients that can have sharp edges or be too intense for daily use.
The rise of K-Beauty in the 2010s also introduced many users to the concept of at-home chemical exfoliation. K-beauty is driven by "skintellectuals" who want efficacious products that deliver on their promised results, and chemical exfoliants, when used appropriately, can be extremely impactful in improving many different aspects of skin appearance and texture.
Hydroxy Acids (HAs) are a class of compounds that have been used to treat skin disorders for about 40 years. Clinical trials show the effectiveness of the ingredients within the HA family in treating photoaging, reducing wrinkles, clearing pores, and improving skin elasticity, tone, and hydration.
Alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs) are the two primary classes of HAs, and in recent years, polyhydroxy acids (PHAs) have also risen in popularity in at-home skincare products and clinical treatments.
AHAs are organic carboxylic acids with one hydroxyl group attached to the α-position of the carboxyl group. The hydroxyl and carboxyl groups are both directly attached to an aliphatic or alicyclic carbon atom, and the hydroxyl group in the AHA is neutral, as only the carboxyl group provides an acidic property.¹
AHAs are present in a lot of natural materials and foods, including milk, sugar, and fruit. Glycolic acid is the smallest and most widely used AHA in skincare and is derived from sugar cane. Lactic acid is the second smallest AHA, is derived from milk, and is widely used in topical skincare products to exfoliate the skin and support anti-aging effects.²
Because of their small size, AHAs act on both the epidermal and the dermal levels, and when applied to the skin, they stipulate the exfoliation of epidermal cells in the stratum corneum by interfering with the ionic bonding between the cells. This process “unglues” the cells, sloughing off dead, dull, and rough skin to promote skin renewal.³
Glycolic Acid Skincare Products, Right to Left: Cane + Austen Miracle Pads, The Ordinary Glycolic Acid 7%, Biossance Squalane + Glycolic Renewal Facial, Naturopathica AHA Purifying Night Serum, Goop Beauty Goop Glow 15% Glycolic Acid Overnight Glow Peel
Early research promoted AHAs to treat hyperkeratosis, but since then, AHAs have evolved to be quite popular to promote soft, smooth skin, decreased wrinkles, reduce age spots, and treat blemishes. AHAs also have the benefit of improving subcutaneous barrier function and restoring hydration by promoting an increase in skin’s levels of hyaluronic acid.
Overuse of AHAs can be dangerous and sensitizing to the skin, resulting in stinging and burning immediately after application. Over-exfoliation compromises the skin’s acid mantle, disrupts the skin’s microbiome, and can increase inflammation and irritation in a detrimental way. They can also promote photosensitivity and AHA skincare products are required to have a sun safety warning on their packaging.
For those who are at risk of damaging their skin due to AHA use, gentler acids are ideal to promote skin cell renewal without the harmful side effects. Less aggressive, time-released products, such as the Twincraft Product Innovation Team development of the Slow & Steady Toner with a time-released AHA active ingredient, are most appropriate for sensitive or sensitized skin.
BHAs are organic carboxylic acids having one hydroxyl group attached to the β-position of the carboxyl group. The hydroxyl group in the BHA is neutral in nature and the carboxyl group provides the acidic property.⁵
Some molecules are considered both an AHA and a BHA because they contain a hydroxyl group in the α-position to one carboxyl group and in the β-position to another carboxyl group, including the aforementioned malic acid and citric acid.
BHAs are exfoliants and are effective at reducing the appearance of fine lines and wrinkles and improving overall skin texture without the irritation often associated with AHAs.
BHA Skincare Products, Right to Left: Tata Harper Regenerating Cleanser, Paula's Choice 2% BHA Lotion Exfoliant, COSRX Low pH BHA Overnight Mask, Hanskin Pore Cleansing Oil, COSRX BHA Blackhead Power Liquid, Baxter of California Skin Concentrate BHA
According to the FDA, BHA ingredients may be listed as:
Salicylic acid is considered the most commonly used BHA in skincare, but many chemists refute the classification of this acid as a true BHA because of how it interacts with the skin on a molecular level. However, most consumers, the FDA, and cosmetic brands refer to it as a BHA and label it as such.⁸
PHAs are organic carboxylic acids with two or more hydroxyl groups in the molecule attached to carbon atoms of an aliphatic or alicyclic chain. All the hydroxyl groups in the PHA are neutral, and only the carboxyl group provides its acidity.⁶
PHAs are naturally occurring compounds that have efficacy levels similar to AHAs but are larger and therefore less sensitizing. PHAs are compatible with clinically sensitive skin, have antioxidant properties, and are well suited for those with rosacea or atopic dermatitis or have recently undergone cosmetic procedures.
PHAs provide moisturizing and humectant properties and can enhance skin barrier function, which increases the skin’s resistance to chemical stress.
Popular PHAs include gluconolactone and lactobionic acid, which are chemically and functionally similar to their AHA counter parts (glycolic acid and lactic acid, respectively), but given their larger molecular structure, they are not able to deeply penetrate the skin and cause the same level of damage while reaping similar benefits.⁷
The Twincraft Skincare Product Innovation Team has explored natural formulations that fall under each of these categories to guide our customers to create product lines that treat the signs of aging, fight acne, and lighten skin pigmentation, and provide other products with the clinical levels of efficacy that our today's shoppers want. Request a sell sheet to learn more about each of these concepts.
Sources: ¹,²,⁵,⁶ Clinical and cosmeceutical uses of hydroxyacids (Green, Rph, MS; Yu, PhD, OMD; Scott, MD) ³Hydroxy Acids, the Most Widely Used Anti-aging Agents https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3941867/ ⁴Paula’s Choice: Alpha Hydroxy Acids for Skin: What are they and how they work https://www.paulaschoice.com/expert-advice/skincare-advice/anti-aging-wrinkles/alpha-hydroxy-acids-skin-what-they-are-how-they-work.html ⁷The use of polyhydroxy acids (PHAs) in photoaged skin. https://www.ncbi.nlm.nih.gov/pubmed/15002656 ⁸ US Food & Drug: Beta Hydroxy Acids https://www.fda.gov/cosmetics/cosmetic-ingredients/beta-hydroxy-acids