What Is Salicylic Acid and How Does It Benefit Skin?

By Renee Jacques and Rebecca Dancer

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What Is Salicylic Acid and How Does It Benefit Skin? | Allure

In the over-the-counter battle against breakouts, there are a few key ingredients you should know about, and salicylic acid is at the top of that list. Simply speaking, salicylic acid is one of acne's biggest enemies. You reach for a spot treatment within the second you see a zit invading your face. You slather it on a blemish overnight and you might wake up in the morning with a pimple that is dried up and much less noticeable. But, what does salicylic acid do for the skin, and what are the best ways to reap its benefits?

To find out, we consulted board-certified dermatologists to help break down exactly how salicylic acid works on the skin, who should (and shouldn't) use it, and why it's a cornerstone ingredient in the battle against breakouts.

Salicylic acid is derived from willow bark, says cosmetic chemist Ron Robinson, and it belongs to a class of ingredients called salicylates. It's structure is a little complicated, but understanding it is important to learning why (and how) it works so well.

When it comes to skin-care products, there are two classes of acids you'll see often: beta hydroxy acids (BHAs) and alpha hydroxy acids (AHAs). "Salicylic acid is a beta hydroxy acid," says cosmetic chemist Randy Schueller. "[This] means the hydroxy part of the molecule is separated from the acid part by two carbon atoms, as opposed to an alpha hydroxy acid where they're separated by one carbon atom."

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.”

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.

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."

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.

Therefore, salicylic acid is ideal for treating blackheads and whiteheads. "Salicylic acid can directly dissolve the keratin plugs and regulate the skin cells," says Dr. Nazarian. “It does have some effectiveness against cystic acne due to its antibacterial activity, but less so than the classic blackheads and whiteheads.”

You can actually use too much salicylic acid. "The primary negative side effect of salicylic acid is its ability to irritate and dry skin in those who are very sensitive or those who overuse it," says Dr. Nazarian.

"Depending on the concentration and the number of applications, some people may experience dryness, peeling, redness, and some skin irritation," says Schueller. For this reason, those with skin that's already severely dry or sensitive should consider avoiding SA altogether. It's also not the best choice if you are pregnant or taking certain medications, including blood thinners.

Still, the concentration of most over-the-counter salicylic acid creams and cleansers — often 2% — is low. “If used appropriately, it can be tolerated quite well,” says Seemal Desai, MD, a board-certified dermatologist in Texas. When starting a new salicylic acid-based product, he advises his patients to begin slowly by using the product every other day (or otherwise half as often as the product directs), then working their way up to daily once they know how their skin reacts to the ingredient.

What can be serious: "Applying salicylic acid or any salicylate to very large portions of your body can lead to salicylate poisoning," says Schueller. So just don't apply a layer of it all over — stick to only acne-prone areas.

Salicylic acid-based products are safe to use daily if used as directed and tolerated by your skin, says Dr. Desai. "I personally have quite oily skin, and I find that salicylic acid daily on my skin type works totally fine," he says. If your skin type is dry or sensitive, it's more likely that salicylic acid could cause some irritation, so be sure to follow Desai's advice as stated above and test the product on your skin every other day before committing to it on a daily basis.

As with many things in life, the answer to this question depends largely on the individual. "Depending on the severity of their acne, I may recommend an [SA-containing] acne wash, such as SkinCeuticals LHA Cleanser, which contains a blend of salicylic acids," says Dr. Wesley. "For mild acne that just occurs every so often, an acne spot treatment can be helpful, especially when applied early."

Dr. Desai is a fan of two classic acne-fighting products that contain salicylic acid: Neutrogena Oil-Free Salicylic Acid Acne Fighting Face Wash and CeraVe Renewing SA Cleanser. "My patients also like Obagi Medical Acne Cleansing Wipes," he says, which contain 2% salicylic acid in a handy wipe for use morning and evening.

Some of our favorite salicylic acid-spiked spot treatments include Clean & Clear Advantage Acne Spot Treatment and Murad Rapid Relief Acne Spot Treatment, both of which contain 2% concentrations of the ingredient.

Speaking of concentrations, the U.S. Food and Drug Administration (FDA) allows manufacturers to make acne-fighting claims for salicylic acid-containing products if they use it at levels between 0.5% and 2%, so that is the full range you'll find in over-the-counter skin-care products. For chemical peels performed at the dermatologist's office, the concentration may be as high as 20 to 30%, Dr. Wesley says.

When adding a new ingredient to your skin-care lineup, it's important to consider how it interacts with those already present in your routine. Luckily, says Dr. Desai, salicylic acid and vitamin C can be used in conjunction "in the correct sequence."

"You wouldn't necessarily use both at the exact same time depending on your skin type and what you're trying to achieve," he says. "But you could use, for example, a salicylic acid cleanser to cleanse your skin — especially if you're acne-prone — and then a topical vitamin C as your antioxidant, used at two separate times of the day. Many patients I have use both.”

Vitamin C can help brighten skin and reduce dark spots, including hyperpigmentation left over from breakouts, so the two ingredients are a natural fit into one skin-care routine for acne-prone folks.

Salicylic acid isn't just for blackheads, according to experts. "At lower levels, salicylic acid can speed up the desquamation process and aid in conditions such as dandruff and seborrheic dermatitis, which are caused by a slowing down of skin cells sloughing off," says Schueller. Pretty cool.

What Is Salicylic Acid and How Does It Benefit Skin? | Allure