A Complete Guide to Salicylic Acid

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Whether you’re prone to full-blown breakouts or a few pesky pimples, the chances are you’ve probably used a product containing salicylic acid. Considered one of the top acne-fighting ingredients in dermatology, salicylic acid is a tried-and-true active, but no so self-explanatory. Here’s what the pros want you to know.

What is salicylic acid?

Commonly used in dermatology to treat a variety of skin conditions and diseases (both over-the-counter and prescription medication), “salicylic acid is an organic compound that is a plant hormone found naturally in the bark of white willow and wintergreen leaves,” says Bloomfield Hills, MI dermatologist Linda C. Honet, MD. “It is one of the oldest, most ubiquitous and most accessible topical medications in dermatology, and it can be found in a variety of skin-care products, cleansers, peeling agents, and prescription compounds, to name a few. It has several important properties and clinical applications, where it can function as an exfoliant, a keratolytic—it can dissolve skin flakes and scales—and an anti-inflammatory, making it a very useful treatment for a variety of skin conditions.”

However, you probably know it best as a betahydroxy acid. “Salicylic acid is the classic example of a betahydroxy acid (BHA), as opposed to alphahydroxy acids like glycolic acid or lactic acid,” explains Campbell, CA dermatologist Amelia K. Hausauer, MD. “This means there is an extra carbon in its backbone structure that separates the hydroxy portion from the acid portion. The difference in structure means BHAs tend to be more oil-soluble than AHAs, so salicylic acid can penetrate through the lipid layers of the skin to get to a deeper level.” New York dermatologist Heidi A. Waldorf, MD adds that not only is salicylic acid “lipophilic—attracted to fat and oil—but also comedolytic—it helps unplug whiteheads and blackheads—so it’s attracted to the sebaceous follicles (pores) where it’s needed.”

What can it be used to treat?

“The fact that salicylic acid can get deeper into the skin and pass through the lipid layer means it is helpful at targeting clogged pores involved in acne,” Dr. Hausauer explains. “It works to dissolve or unglue skin debris that congests pores, and it has anti-inflammatory properties that can also help minimize inflamed red pimples and pustules, allowing for faster resolution and clearing. Three major factors contribute to acne: abnormal sloughing of skin cells forming a plug, excessive oiliness and actions of P. acnes bacteria. Salicylic acid targets the first mechanism by dissolving the keratin plug and better regulating cell interactions. Thus, it works most effectively for treating blackheads and whiteheads.”

“The fact that it can break down skin cell connections also makes it an exfoliator,” adds Dr. Hausauer. “It is also good for seborrheic dermatitis or dandruff: T/Sal is an example of a shampoo/scalp treatment that can help slough off that flaky skin.” Other skin conditions that can be treated with the salicylic acid include warts, calluses, keratosis pilaris, and even psoriasis, but always consult a doctor before experimenting at home.

At higher doses, Dr. Honet says salicylic acid can also be used in-office as a deep chemical peel to treat precancerous lesions called actinic keratoses (a rough, scaly patch on the skin that develops from years of sun exposure). Dr. Hausauer uses salicylic acid chemical peels to treat her acne-prone patients as well.  

What skin types is it best for?

According to Dr. Honet, salicylic acid is very well tolerated by the majority of skin types, and only the very sensitive or very dry may have difficulty. “Not only is it quite gentle at low concentrations, but the percentage can also be varied from very low to quite high to take advantage of its various properties and penetrability,” she explains. “The other valuable aspect of salicylic acid is that it is often combined and compounded with other medications to amplify specific therapeutic properties of the active ingredients.” Dr. Waldorf says it’s also safe for all skin colors and unlikely to cause hyperpigmentation. (“It also has the advantage over benzoyl peroxide of not bleaching clothing or towels.”)

Are there any ingredients you shouldn’t mix with it, or any side effects?

The most common side effects are dryness, redness and irritation, and Dr. Honet points out that though salicylic acid is typically gentle, if used in conjunction with other active ingredients that cause the same effects, they may be amplified, and the skin may become overly irritated. “However, and interestingly, some of the most popular skin-care products combine both an alphahydroxy acid, like glycolic acid, and salicylic acid in one, to more effectively exfoliate, improve skin texture, and improve blackheads, whiteheads and pores.”

If you’re pregnant, Dr. Hausauer says that although between 0.5 percent and 2 percent is sold over the counter and generally probably safe in pregnancy, it is not recommended in high doses or over large areas. “When used in large amounts, it can also potentially interact with blood thinners, and don’t apply a layer over the full body—just acne-prone areas—to minimize the risk of enough systemic absorption to salicylate poisoning.”

Can it be used as a spot-treatment and all over the skin?

Salicylic acid is effective for the spot-treatment of acne pimples and oily T-zones; Dr. Honet says it is also used in spot-treating warts and calluses, and is found as the active ingredient in over-the-counter foot-care products. “For all-over face and body treatment, it can be found as the active ingredient in cleansers, shampoos, lotions, gels, and exfoliators to treat skin conditions like dandruff, keratosis pilaris (chicken skin), rough patches on knees and elbows, and cracked skin on heels,” she explains.

However, Dr. Hausauer cautions users to watch the area being treated versus the strength of the medication. “It’s fine to apply to the body—like the back or chest if these are areas that break out—but for bigger areas, consider selecting a lower-strength formulation.”

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