BHA for closed comedones: how should you use it?

When your skin isn't stinging, use one salicylic acid product, once a day, starting where the tiny bumps cluster. Salicylic acid (BHA) is an ingredient with trials showing fewer comedones on human faces. A leave-on product (toner, serum or cream) made for the Korean market tops out at 0.5%, and US labeling rules also say to start once a day. Applying it only where the bumps cluster is a common way to limit irritation, but it has not been tested in a trial.

Is there evidence for salicylic acid on closed comedones?

Of seven acne drugs in use at the time, only salicylic acid and tretinoin reduced microcomedones (the stage before a visible bump) on the face (Mills & Kligman, 1983). Only the 2% salicylic acid cleanser, not the 10% benzoyl peroxide wash it was compared with, significantly reduced comedones (Shalita, 1989). Trials with a few dozen participants found salicylic acid reduced closed comedones, but an analysis that pooled many trials and 3,880 participants could not reach a firm conclusion (Liu et al., 2020). So keep salicylic acid as something worth trying, without pushing the strength or frequency up in a hurry for results. How comedones relate to exfoliation is in Comedones that won't clear — why exfoliating misses them

If you use salicylic acid, what strength and how often?

In Korea, general leave-on cosmetics may contain up to 0.5%, the preservative limit, and rinse-off cleansers up to 2% (Korean cosmetic safety standards). A 2% cleanser used over the whole face is an option. The US lists 0.5 to 2% as an over-the-counter acne drug ingredient and requires labels to say to start once a day because skin can get too dry (21 CFR 333). Whether it's a leave-on product or a cleanser, start salicylic acid once a day. It's best not to layer a leave-on product and a cleanser on the same day.

When should you pause salicylic acid?

If your face stings or burns after cleansing, or a product you have been using suddenly stings, your barrier is signalling that it is weak. We found no trial that applied salicylic acid to skin with a weakened barrier. So we suggest a short break, the same as after over-exfoliating. While the stinging lasts, pause salicylic acid and keep only a low-pH cleanser and moisturizer. When to start again is in Over-exfoliated — how do I calm it down?

In short, salicylic acid goes low, local and alone

Salicylic acid can loosen the bonds between skin cells so built-up flakes come away (Arif, 2015). US labeling rules warn that using it with other topical acne products makes irritation and dryness more likely (21 CFR 333). Korea's 0.5% leave-on limit is a preservative standard, so products that make no claim can still contain it. When your skin isn't red or stinging, try salicylic acid once a day on the bumpy areas only. And keep in mind that layering it with other exfoliating ingredients or retinol can bring more irritation and dryness.

One step today

• Count the products whose ingredient lists include salicylic acid, glycolic acid, lactic acid or retinol, and if there are two or more, keep just one. This follows the US labeling warning that combining topical acne products makes irritation and dryness more likely (21 CFR 333). Counting retinol, glycolic acid and lactic acid too is a common way to limit irritation. Capryloyl salicylic acid and betaine salicylate sound similar but are different ingredients. Once you are down to one, carry on if there is no stinging within 10 minutes of cleansing; if stinging hasn't settled after a 2 to 4 week break, see a dermatologist.
• Use the one you kept once a day, and if it's a leave-on product, apply it only where the bumps cluster. Starting once a day follows US labeling rules (21 CFR 333). If your skin gets dry or peels, drop to every other day; if swelling, blisters or oozing appear, stop that day and see a dermatologist. If the number of bumps hasn't changed after 8 to 12 weeks, they may not be comedones, so get them checked.