A beta hydroxy acid or β-hydroxy acid (BHA) is an organic compound
that contains a carboxylic acid group and hydroxy group separated by two carbon atoms. A α-Hydroxy acids, or alpha hydroxy acids (AHAs),
is a organic compound that consist of a carboxylic acid group
substituted with a hydroxyl group on the adjacent carbon.
These two hydroxy acidsare closely related with AHA having one carbon atom instead of two separating the groups.
The main difference between alpha hydroxy acids and
beta hydroxy acid is their lipid (oil) solubility. Alpha hydroxy acids
are water soluble only while beta hydroxy acid is lipid (oil) soluble.
This means that beta hydroxy acid is able to penetrate into the pore
which contains sebum and exfoliate the dead skin cells that are built up
inside the pore. Because of this difference in properties, beta hydroxy
acid is better used on oily skin with blackheads and whiteheads. Alpha hydroxy acids are better used on thickened, sun-damaged skin where breakouts are not a problem.
Currently in cosmetics, Salicylic acid is the only beta hydroxy acid used.