BHA stands for beta hydroxy acid, and in skincare, it almost always means one specific ingredient: salicylic acid. It’s a chemical exfoliant that works by loosening dead skin cells and clearing out pores from the inside, making it one of the most effective over-the-counter treatments for acne, blackheads, and oily skin. If you’ve seen BHA on a product label or in a skincare routine, here’s what it actually does and how to use it.
How BHA Works on Your Skin
Salicylic acid is oil-soluble, which is the single most important thing to understand about it. That oil solubility allows it to cut through the sebum (oil) inside your pores and exfoliate below the skin’s surface, not just on top of it. This is what separates BHA from most other exfoliants.
Once it penetrates a pore, salicylic acid increases the water content of the outer layer of skin, causing that layer to swell, soften, and shed. The result is that dead cells packed inside the pore loosen and flush out rather than staying trapped and forming a clog. At the same time, it slows the rate at which oil-producing cells generate new lipids, so your skin produces less of the excess sebum that leads to breakouts in the first place.
BHA also has genuine anti-inflammatory properties. It reduces the signaling molecules that drive redness and swelling around acne lesions. So it’s doing three things at once: exfoliating, reducing oil, and calming inflammation.
What BHA Is Best For
BHA is particularly well suited for oily and acne-prone skin. Because it works inside the pore, it’s the go-to ingredient for:
- Blackheads and whiteheads. These form when dead skin and oil plug a pore. BHA dissolves that plug.
- Inflammatory acne. The anti-inflammatory action helps reduce the red, swollen pimples that come from bacterial overgrowth in clogged pores.
- Enlarged pores. Consistently clearing out pore congestion can make pores appear smaller over time.
- General oiliness. By reducing lipid production in sebaceous cells, BHA helps control shine.
If your skin is dry, sensitive, or not prone to breakouts, BHA may not be the best exfoliant for you. AHAs (alpha hydroxy acids) like glycolic acid or lactic acid are typically a better fit for dry or sun-damaged skin, since they work on the surface to improve texture and tone without diving into pores.
BHA vs. AHA: The Key Difference
AHAs are water-soluble. They exfoliate the surface of your skin and the very top layers, which makes them effective for dullness, fine lines, and uneven pigmentation. BHA is oil-soluble, so it does everything AHAs do on the surface while also penetrating into the pore lining. If your main concern is congestion and breakouts, BHA is the stronger choice. If your concern is texture, tone, or signs of aging on otherwise clear skin, AHAs tend to deliver more.
There’s another practical difference worth knowing. A study comparing 10% glycolic acid and 2% salicylic acid found that glycolic acid significantly increased the skin’s sensitivity to UV radiation, measured by greater redness, more DNA damage, and more sunburn cells after UV exposure. Salicylic acid did not increase UV sensitivity at all compared to untreated skin. So while you should still wear sunscreen with any exfoliant, BHA carries less inherent photosensitivity risk than AHAs.
Concentrations You’ll Find in Products
Most over-the-counter BHA products contain salicylic acid at concentrations between 0.5% and 2%. A 2% salicylic acid product is the standard strength for treating acne and is the concentration used in most clinical studies. Products at 0.5% are gentler and work well for maintenance or for skin that’s easily irritated. When salicylic acid appears as a preservative in non-exfoliating products like moisturizers or sunscreens, it’s capped at 0.5% under EU cosmetics regulations.
The pH of the product matters too. BHA needs an acidic environment to work properly, generally in the pH range of 3 to 4 for dedicated exfoliating treatments. At higher pH levels, less of the salicylic acid is in its “free” form, which is the form that actually penetrates skin. However, very low pH also increases the risk of irritation. Well-formulated products balance this tradeoff. If you’re using a basic cleanser or toner with salicylic acid listed far down the ingredient list, the pH may not be low enough for meaningful exfoliation.
Other Forms of BHA
Salicylic acid is sometimes listed under related names. Willow bark extract is a natural source of salicin, which the skin can convert to salicylic acid, though it’s generally milder and less predictable in strength. Some Korean skincare brands use betaine salicylate, a compound that pairs salicylic acid with betaine (derived from beets) to reduce irritation.
Research on betaine salicylate is promising. In a 28-day clinical trial, it outperformed salicylic acid across the board, reducing acne lesions by about 38% compared to 24% for salicylic acid alone, while also showing significantly lower irritation and cytotoxicity. It achieved stronger anti-inflammatory effects and better antibacterial activity against the bacteria involved in acne. If you find salicylic acid too harsh, betaine salicylate is worth trying.
What Purging Looks Like
When you start using BHA, your skin may go through a phase called purging. Because salicylic acid speeds up the rate at which skin cells turn over, clogs that were forming deep in your pores get pushed to the surface faster than they normally would. This can look like a wave of new breakouts, which understandably feels like the product is making things worse.
Purging has a few distinguishing features. It shows up in areas where you already tend to break out, not in new locations. The individual pimples appear and resolve faster than your usual breakouts. And it should be over within four to six weeks, which is roughly one full skin cell turnover cycle. If you’re breaking out in places that are unusual for you, or if the irritation lasts beyond six weeks, that’s more likely a reaction to the product rather than purging.
How to Fit BHA Into a Routine
BHA comes in many formats: cleansers, toners, serums, spot treatments, and leave-on liquids. Leave-on products (serums, toners, liquids) give salicylic acid more time in contact with your skin and generally deliver stronger results than a cleanser that rinses off after 30 seconds. If you’re new to BHA, starting with a cleanser or using a leave-on product every other day lets you gauge your skin’s tolerance before increasing frequency.
You can use BHA alongside most other active ingredients, but layering it with multiple strong actives in the same session increases the chance of irritation. If you’re also using a retinoid, consider alternating nights rather than applying both at once. Vitamin C serums (L-ascorbic acid) can be used in the same routine, typically applied after BHA has absorbed, though some people find the combination too much for sensitive skin. The practical rule is simple: if your skin feels tight, stinging, or looks red and flaky, you’re overdoing it. Scale back to fewer nights per week and build up gradually.
Apply BHA to clean, dry skin. If you’re using a leave-on product, give it a few minutes to absorb before layering your moisturizer on top. Even though BHA doesn’t increase UV sensitivity the way AHAs do, daily sunscreen remains important, especially since exfoliation of any kind reveals fresher, less-weathered skin underneath.