Salicylic acid is a widely available over-the-counter ingredient that addresses an expansive range of skin concerns — from acne to fine lines and even calluses. It comes in many different formulas and strengths, depending on the issue at hand.

So how can you tell what concentration you need — and whether you should ask your dermatologist about a prescription for salicylic acid? We’ve got your answers.

How does salicylic acid work?

This beta hydroxy acid is most commonly described as an oil soluble exfoliant — meaning it can penetrate into the skin’s protective lipids and help shed dead skin cells. Though historically salicylic acid has been referred to as a keratolytic (meaning it breaks down keratin protein) it’s technically a desmolytic — weakening the desmosome junctions that bind skin cells together.

A relative of aspirin, salicylic acid also has anti-inflammatory properties. This means it’s good at calming redness, swelling and irritation that results when your skin’s immune function gets triggered.

What strength of salicylic acid is available over the counter?

The properties of this BHA make it well suited to addressing quite a variety of skin concerns: most notably conditions involving excess skin cell buildup in the stratum corneum. It’s available in a range of formulas — including cleansers, gels, lotions, creams, ointments, pre-soaked pads, and foam.

Salicylic acid is regulated as a drug by the FDA, which means that manufacturers of over-the-counter products have to follow labeling and dosage requirements outlined in a rulebook called a monograph. These guidelines are organized by category, so different skin conditions have different rules. Here are the over-the-counter concentrations allowed for each:

• Acne: 0.5% to 2%
• Dandruff, seborrheic dermatitis, psoriasis: 1.8% to 3%
• Corns and calluses: 12% to 40% depending on the treatment method
• Warts: 5% to 40% depending on the treatment method

Is salicylic acid available by prescription?

Higher strengths of salicylic acid are often prescribed by dermatologists in cases where over-the-counter treatments prove unsuccessful. It’s most often used in stronger concentrations for scaly skin conditions and warts — not as much for acne.

Research also suggests that salicylic acid in combination with other drugs is beneficial for the treatment of precancerous actinic keratoses — dry, rough patches of skin caused by UV damage.

High concentration salicylic acid has also been studied for its role in chemical peeling: both for medical and professional cosmetic use. BHA peels range from about 10% salicylic acid for treating comedones, 30% for typical photodamage, to 50% to remove actinic lesions.

Can you get higher concentrations of salicylic acid without a prescription?

A quick Internet search turns up a host of sites eager to sell high potency salicylic acid — anywhere from 10% to a whopping 50% — no questions asked. You probably know what we’re going to say: please don’t try it. Salicylic acid is FDA regulated for a reason: strong concentrations can cause all sorts of side effects, from simple irritation and redness to burns, permanent scarring, and severe allergic reactions.

Instead, start with an over-the-counter product that’s made specifically for your skin concern — if you don’t get results, talk to your dermatologist about other options.

Here’s a roundup of SLMD favorites:

• Salicylic Acid Cleanser: a gentle, everyday exfoliant that’s part of our Acne System
• Salicylic Acid Spot Treatment: a roll-on with maximum-strength BHA
• Salicylic Acid Pimple Patches: transparent patches loaded with salicylic acid
• Clear Out: a treatment mask with sulfur and zinc oxide for face and body
• AHA/BHA Swipes: pre-soaked pads that are also great for well aging
• Salicylic Acid Body Spray: post-shower or workout treatment that’s also great for preventing maskne

Dr. Lee’s last word

It’s no secret that I’m a huge fan of salicylic acid, especially for managing acne like blackheads and whiteheads. It’s also a great everyday exfoliant that can help prevent signs of premature aging. You can get it over the counter, and we dermatologists use it at higher concentrations for peels and for managing a variety of skin conditions.

—Dr. Sandra Lee