Difference Between Alpha and Beta Hydroxy Acids

The key difference between alpha and beta hydroxy acids is that the alpha hydroxy acid (AHA) has a carboxylic acid group and a hydroxyl group separated by one carbon atom whereas a beta hydroxy acid (BHA) contains a carboxylic acid group and a hydroxyl group separated by two carbon atoms.

Hydroxy acids are organic compounds both having a carboxylic acid group and a hydroxyl group in the same molecule. The carbon atoms to which these functional groups are attached are in close proximity. Therefore, we can name them as alpha, beta or gamma, according to the number of carbon atoms that separate these functional groups. Let us discuss more details in the below text.

1. Overview and Key Difference
2. What are Alpha Hydroxy Acids
3. What are Beta Hydroxy Acids
4. Side by Side Comparison – Alpha vs Beta Hydroxy Acids in Tabular Form
5. Summary

What are Alpha Hydroxy Acids?

Alpha hydroxy acids (AHAs) are organic chemical compounds having a carboxylic acid group substituted with a hydroxyl group on the adjacent carbon atom. That means one carbon atom separates these the two functional groups, carboxylic acid group (-COOH) and hydroxyl group (-OH). There are two types, namely, natural AHA and synthetic AHA.

The well-known application of these compounds is in the cosmetic industry. Manufacturers use this compound as an essential ingredient in many skincare products due to its ability to reduce wrinkles and improve the overall look of the skin. The manufacturers obtain the AHAs that we use in the cosmetic industry mainly from food products such as glycolic acid, (obtained from sugar cane), lactic acid (obtained from milk), citric acid (obtained from citrus fruits), etc. In chemical applications, these compounds are important as precursors for the chemical synthesis of aldehydes via oxidative cleavage.

What are Beta Hydroxy Acids?

Beta hydroxy acids (BHAs) are organic chemical compounds having a carboxylic acid group substituted with a hydroxyl group on the second adjacent carbon atom. This means that the two carbon atoms separate the two functional groups, carboxylic acid group (-COOH) and hydroxyl group (-OH). These molecules are hence, closely related with AHAs.

Difference Between Alpha and Beta Hydroxy Acids

Figure 01: Different Hydroxy Acids (alpha – α, beta – β and gamma – γ hydroxy acids)

When considering the acidity of the compound, it is less acidic than AHA. This is because of the large distance between the two functional groups compared to AHAs. Beta hydroxy acids are also find use in the cosmetic industry. However, manufacturers use this term mainly as a synonym for salicylic acid. This salicylic acid is an important ingredient in anti-aging creams as well as acne treatments.

What is the Difference Between Alpha and Beta Hydroxy Acids?

Alpha hydroxy acids (AHAs) are organic chemical compounds having a carboxylic acid group substituted with a hydroxyl group on the adjacent carbon atom. Hence in these, one carbon atom separates these the two functional groups, carboxylic acid group (-COOH) and hydroxyl group (-OH) of AHAs. Beta hydroxy acids (BHAs) are organic chemical compounds having a carboxylic acid group substituted with a hydroxyl group on the second adjacent carbon atom. Therefore, in these molecules, one carbon atom separates the two functional groups, carboxylic acid group (-COOH) and hydroxyl group (-OH) are of BHAs. This is the main difference between alpha and beta hydroxy acids.

Summary – Alpha vs Beta Hydroxy Acids

Both AHAs and BHAs are important ingredients of skincare products in the cosmetic industry. The difference between alpha and beta hydroxy acids is that alpha hydroxy acid has a carboxylic acid group and a hydroxyl group separated by one carbon atom whereas a beta hydroxy acid contains a carboxylic acid group and a hydroxyl group separated by two carbon atoms.

Reference:

1. “Alpha Hydroxy Acid.” Wikipedia, Wikimedia Foundation, 3 July 2018. Available here
2. “Beta Hydroxy Acid.” Wikipedia, Wikimedia Foundation, 7 June 2018. Available here