Skincare Acids: AHA, BHA, and PHA

In esthetics school, we learn the basics of alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs), commonly found in skin care products and in chemical peeling. But understanding acid’s features and benefits, let alone the science, can be easily forgotten or misunderstood—especially when students are trying to learn all there is to know about the skin in such a short amount of time.  

What is the difference between AHAs and BHAs? 

Simply, AHAs are considered water soluble, and BHAs are considered oil soluble. More specifically, AHAs are a family of naturally occurring acids that vary in molecular size and are used extensively in skin care products, primarily as exfoliation agents. This group of acids includes glycolic, lactic, malic, mandelic, and tartaric acids. Although AHAs are found in many fruits and plants, most are produced synthetically to ensure safety and consistency.  

BHAs are an organic compound with antibacterial properties. Also called salicylic acid, BHAs help to loosen and slough dead cells from the skin’s surface. The oil-soluble nature of this acid enables it to get deeper into follicles to break up sebum and cell impactions. 

The science 

Both AHAs and BHAs are organic compounds, meaning they contain carbon. Carbon is bonded to oxygen and hydrogen, otherwise known as a hydroxl group (-OH). This bond occurs either on the first carbon atom (alpha) or second carbon atom (beta)—thus defining alpha hydroxy acids and beta hydroxy acids.  

Polyhydroxy acids 

Of course, there’s more to acids than just the basic AHAs and BHAs. Polyhydroxy acids (PHAs) are not new to the scene, but they are the acid trending for the moment. As you may have guessed, PHAs contain carbon bonded to oxygen and hydrogen on both the first and second positions. In other words, they’re bonded in many positions. Poly means many.  

PHAs are as effective as AHAs without the typical downsides, making them a good option for sensitive skin. They contain antioxidant properties, are not photosensitizing, are not irritating, and are considered moisturizing. Some common PHAs include: 

  • Lactobionic Acid 
    • Oxidized form of lactose 
    • Exfoliates 
    • Brightens 
    • Increases epidermal thickness 
    • Gentle, acts like a humectant and as an antioxidant 
  • Gluconolactone 
    • Sometimes listed as gluconic acid 
    • Naturally occurs in fruit, honey, and wine 
    • Exfoliates  
    • Hydrates 
    • May have some antimicrobial properties 
    • Improves texture and tone 
  • Galactose 
    • The sugar found in milk 
    • Humectant, antioxidant, and anti-inflammatory 



Dermacare Direct. “What Are Hydroxy Acids.” Last modified July 25, 2011. 

INCI Guide. “Galactose.” 

Diana Tran, et al. “An Antiaging Skin Care System Containing Alpha Hydroxy Acids and Vitamins Improves the Biomechanical Parameters of Facial Skin.” Clinical, Cosmetic and Investigational Dermatology 8. (December 2014). 

Joshua A Zeichner. “The Use of Lipohydroxy Acid in Skin Care and Acne Treatment.” Journal of Clinical Aesthetic Dermatology 9 no. 11. (2016). 

Andrija Kornhauser, Sergio G. Coelho, and Vincent J. Hearing. “Applications of Hydroxy Acids: Classification, Mechanisms, and Photoactivity.” Clinical, Cosmetic and Investigational Dermatology 3. (November 2010). 




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