COSRX Niacinamide 2% + BHA 4% Blackhead Exfoliant vs Some By Mi AHA-BHA-PHA 30 Days Miracle Toner

How they differ

Chemical exfoliation is the common ground: acids that loosen tired surface cells rather than a scrub buffing them off. Past that the two barely overlap. The COSRX is a treatment you dab on congested areas; the Some By Mi is a toner you sweep over the whole face. Same shelf, same shoppers, different jobs — and the acid each one uses is why.

The COSRX is one acid with one target. It’s built on 4% betaine salicylate, a gentler derivative that delivers salicylic acid to the skin. Salicylic acid is oil-soluble, and that is the whole point: a blackhead is a pore packed with oil and dead skin, so an acid that only mixes with water has no way in. A 2015 review of salicylic acid as a peeling agent sets out that oil solubility and its use against comedones — though it reviews the 20–30% peels a clinician applies and rinses, not a 4% derivative you leave on, so read it for the mechanism and not the strength. The rest of the formula is calming: 2% niacinamide, panthenol, no added fragrance or alcohol.

The Some By Mi works the other way: a light touch spread across the whole face. It carries three families of acid at low strength: an AHA (citric acid, sitting low enough that it does more for pH than exfoliation), salicylic acid as the BHA, and lactobionic acid as the PHA. A PHA is a larger, slower molecule, and the gentlest of the three. The tolerability case for PHAs rests on work like a 2004 Cutis comparison, where over twelve weeks people using gluconolactone reported significantly less stinging and burning than those on glycolic acid. Two caveats worth carrying: that trial ran on photoaged skin and tested gluconolactone, not the lactobionic acid in this bottle, and its authors worked for the company that commercialized PHAs. Kept low across all three acids, the blend is mild enough for daily use. The trade is that it smooths the surface and leaves the inside of a pore alone, and it arrives with added fragrance and a little peppermint oil. If you want the full rundown on how the acid families split the work, our guide to Korean exfoliating acids lays it out.

Who each one suits

Reach for the COSRX if blackheads and congestion are the specific thing you want gone: the bumpy, clogged feel around the nose and chin, the pores that fill back up no matter how often you scrub. An oil-soluble acid is the one that gets down into that plug, and the fragrance-free formula means you can use it on skin that scent would otherwise needle. What it won’t do is smooth the whole face or even out texture across the cheeks — it’s pointed at pores, and a mild dose at that, so long-set blackheads take weeks of steady use rather than days.

Choose the Some By Mi if what you want is quiet, all-over maintenance: a light daily pass that keeps oily, blemish-prone skin ticking over and the surface a touch smoother, without committing to a strong active. The low dose makes it an easy first acid for anyone nervous about exfoliation. The catch is the fragrance and peppermint oil. Gentle acids and added scent pull in opposite directions, and scent is the half that reactive skin reacts to — so if yours flushes or stings at the first hint of it, this isn’t the one.

Can you use both?

The answer here is mostly no, or at least not the way you can layer a hydrator and a serum. These do the same category of job, and running two chemical exfoliants over the same skin is the fast route to over-exfoliation — tightness, flaking and a stripped, stinging feeling. Pick the one that matches your main complaint and let it work.

If you’re set on both, treat them as doing separate jobs on separate days: the Some By Mi for light all-over upkeep on the nights you use it, the COSRX saved for the congested zones and never stacked on top of the toner the same evening. Sun protection is not optional with either of them: exfoliated skin burns faster, and the American Academy of Dermatology sets the floor at broad-spectrum SPF 30. Put it on every morning you use an acid the night before.

The answer

Buy the COSRX exfoliant if your problem is blackheads and congestion and you want a fragrance-free acid that reaches them, a few nights a week on the oily zones. Buy the Some By Mi toner if you want gentle all-over upkeep daily and your skin tolerates a little fragrance — it’s one of our picks in the best Korean toners roundup. Still stuck? Go with whichever complaint you’d name first: the pores, or the texture.