Are you still with us? Good, because this is where it gets fun. "This structure is important because it makes salicylic acid more oil-soluble so it can penetrate into the pores of the skin," Schueller says.
Both alpha and beta hydroxy acids exfoliate the skin, but AHAs are water-soluble, while BHAs are oil-soluble, explains New York City-based board-certified dermatologist Sejal Shah, MD. Examples of AHAs, for reference, include glycolic and lactic acids.
"Generally, oil-soluble ingredients penetrate through the lipid layers between the skin cells more readily," Dr. Shah explains. In other words, oil-soluble ingredients can penetrate the skin at a deeper level than their water-soluble counterparts.
Robinson sums up their differences succinctly: "AHAs work well on the skin's surface to loosen old, dead skin and reveal fresh newer skin," he says. “Salicylic acid works deeper [and is] able to penetrate into the pores to unclog them.”
What does salicylic acid do for the skin?
Salicylic acid can get deep into your skin to do its job. This quality is precisely what makes it such a potent ingredient for targeting acne — especially for blackheads and whiteheads.
Once it penetrates the skin, salicylic acid "dissolves skin debris that clogs pores, [acts] as an anti-inflammatory, and also helps red, inflamed pimples and pustules go away faster," explains Naissan O. Wesley, MD, a board-certified dermatologist in Los Angeles.
The ingredient can penetrate so deeply into skin that actually breaks down the connections between skin cells, according to Schueller and Dr. Wesley. "Once it has penetrated the skin, the acid part of the molecule can dissolve some of the intracellular 'glue' that holds skin cells together," says Schueller.
Salicylic acid is also an exfoliant.
This breaking down of skin cells promotes exfoliation. Salicylic acid is considered a keratolytic medication, which means that it's perfect for supreme exfoliation. "Keratolytic medications cause softening and sloughing of the top layer of skin cells," says Rachel Nazarian, MD, a board-certified dermatologist in New York City.
Salicylic acid also loosens and breaks apart desmosomes (attachments between cells in the outer layer of skin). "This 'desmolytic' action encourages exfoliation of skin and unclogging of pores," says Sue Ann Wee, MD, a board-certified dermatologist in New York City.
"One thought etiology of acne is that the skin cells do not behave normally, and rather than sloughing off through a healthy skin cell cycle, they stick together and clog the pores, creating cysts and blackheads," says Dr. Nazarian. "Salicylic acid aids in removing and loosening these skin cells and helps to dissolve the blackheads."
Salicylic acid works best on blackheads and whiteheads.
Schueller says there are three factors that contribute to acne: an abnormal sloughing off of skin cells, excessive oiliness, and the action of P. acnes bacteria. "Salicylic acid helps with the first cause by dissolving the type of skin debris that clogs pores and causes acne," he says.
