What is BHA?
BHA is short for Beta Hydroxy Acids. According to the US FDA, salicylic acid (or related substances, such as salicylate, sodium salicylate, and willow extract)* is often referred to as a BHA in the cosmetics industry, even though from a strict chemistry standpoint, it is not a BHA. Beta hydroxybutanoic acid, tropic acid, and trethocanic acid are also BHAs.
Why is BHA used in Skincare?
BHAs, such as salicylic acid, are very similar to AHAs except that they are oil soluble in contrast to the water soluble AHAs. This is why they are especially useful for oily skin and open pores. The anti-inflammatory effect of BHAs (e.g. salicylic acid) and their comparative compatibility with sensitive skin make BHA especially valuable ingredients.
*The FDA suggests you give yourself extra protection from UV when using BHA products*