What are Hydroxy Acids?

Skin Care
Hydroxy Acids

Along with retinoids and vitamin C, hydroxy acids (HA) are among some of the most well-documented topical compounds in the field of dermatology. While glycolic and salicylic acid remain the most prevalent and ubiquitous, several new additions have been making waves in the cosmetic and medical industries such as lactobionic acid. But before we discuss specific hydroxy acids, we need to know what they are.

What defines a hydroxy acid? 

Hydroxy Acid Definition Structure

The most basic definition of an HA is a carboxylic acid, which is an organic acid that has at least one carboxyl (carbon double-bonded to oxygen) group. However, that general definition includes unrelated compounds like retinoic acid, L-ascorbic acid, and azelaic acid. Therefore, further qualifications need to be identified.

How do they differ from each other?

Four Kinds Types of Hydroxy Acids

There are four types of HAs: Alpha HA (AHA)Beta HA (BHA)Salicylic Acid (SA), and Poly-HA (PHA).

  • AHAs are carboxylic acids with one hydroxyl group attached at the “Alpha” position of the carboxyl group, meaning that the two functional groups are separated by ONE carbon atom. AHAs include the glycolic, lactic, and phytic acids.

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And that’s a wrap! I hope this clarified the structural differences between the various HAs that are encountered in cosmetic formulations. I know this post is short compared to my usual novels, but I’ve decided to break down this topic discussion into THREE parts. Tomorrow, we’ll be talking about HOW the various HAs are used, and WHAT their mechanisms of action are. Part III will be about the common misconceptions of HAs. So stay tuned!

Contributing author: John Su

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2 thoughts on “What are Hydroxy Acids?

  1. aky_17 says:

    So are you saying that BHA and salycilic acid are different? Because as I know, Paulas Choice BHA 2 liquid contains 2% of salycilic acid. It is a bit confusing for me… Thanks

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