Acid season: AHA vs BHA explained

October is when the acids come back out. Summer leaves its mark in quieter ways than a tan line: a roughness under the fingertips, a flatness in the bathroom mirror, a few more blackheads around the nose than you remember signing up for. Weeks of sunscreen, humidity and late evenings will do that. The answer is not a shelf of peels. It is one exfoliant, chosen well.

So, AHA vs BHA? The short answer: AHAs, or alpha hydroxy acids, work on the surface of the skin and suit rough texture and dullness. BHA, or beta hydroxy acid, which in skincare almost always means salicylic acid, dissolves in oil. That lets it work inside the pore, which makes it the better match for oily skin and blackheads. Choose by concern, start slowly and let the formula set the pace.

Your skin sheds constantly. Fresh cells move up from below while the oldest ones at the surface loosen and fall away, a process called desquamation. Most of the time you never notice it happening. When it slows, or when those cells cling on a little longer than they should, you notice the result instead. Light hits an uneven surface and scatters, so skin reads as flat rather than luminous. Makeup catches on dry patches. Inside the pore, that same build up mixes with sebum, the oil your skin produces. The result settles into blackheads and the small bumps that never quite become breakouts.

Exfoliating acids speed that shedding along. As chemical exfoliants, they loosen the bonds holding dead cells together so they lift away more evenly. That is why skin feels smoother after consistent use rather than scrubbed.

Autumn makes a natural starting point. UV levels in Ireland are lower through autumn and winter. That matters because some acids leave skin more sensitive to the sun. Skin also tends to arrive at this time of year carrying the summer’s leftovers: congestion from heavier sunscreens and texture that crept in over the warmer months. If you are still in recovery mode, our post summer skin reset covers the groundwork first.

Pick one. That is the whole brief.

For blackheads and oily skin: a leave on BHA

Obagi CLENZIderm M.D. Pore Therapy is the one to start with if blackheads and visible pores are the issue. It is a 2% salicylic acid liquid swept over the skin after cleansing, so it keeps working in the pore long after you have finished your routine. The light liquid texture suits oily and combination skin that dislikes anything heavy. New to the brand? Here is where to start with Obagi.

For texture and dullness: a wash off AHA

Reform Skincare Glycolic Acid Foaming Cleanser brings glycolic acid into a step you already take. It clears makeup and oil while dissolving the dull, uneven surface layer. That makes it a considered way into acids for anyone who wants smoother looking skin without adding a new product. Reform is also an Irish brand, which we like.

For blemishes and early signs of ageing: AHA and BHA in one cleanser

SkinCeuticals Blemish + Age Cleansing Gel pairs salicylic and glycolic acids in a lightweight gel. It decongests pores and refines texture without leaving skin tight. It suits skin that still breaks out while starting to show signs of ageing.

For a gentler, ready to use option: the pad

Medicube Zero Pore Pad Mild uses lactic acid, one of the gentlest AHAs, alongside panthenol, a form of vitamin B5 that helps soothe and hydrate. Pre soaked pads take the guesswork out of application. That makes them a calm introduction for anyone new to acids.

What goes around it

Keep the rest of the routine simple: a gentle cleanser if your acid is a leave on, a moisturiser that supports the skin barrier and a broad spectrum SPF every morning. While your skin adjusts, keep a second exfoliant or a strong vitamin C off the same night. If retinol is already part of your routine, give it its own evenings.

Both are chemical exfoliants, meaning they use acids rather than grains to clear away dead skin cells. With consistent use, both smooth texture and brighten the look of dull skin. The difference is where they work.

AHA (alpha hydroxy acid)

Water soluble, so it works on the surface of the skin. Glycolic acid has the smallest molecule and works quickly. Lactic acid is larger and gentler, with a hydrating quality that suits drier or more reactive skin. Mandelic acid is larger again and slower to absorb. Best for rough texture, dullness and skin that looks tired.

BHA (beta hydroxy acid)

Oil soluble, so it can travel through the sebum in a pore and clear it from the inside. Salicylic acid is the BHA you will see in skincare. It also has a calming effect on the skin, a property it shares with its chemical relative, aspirin. Best for oily skin, blackheads, visible pores and congestion.

AHA and BHA together

Some formulas combine the two, treating the surface and the pore in one step. These suit skin dealing with blemishes and early signs of ageing at the same time.

Both acids have research behind them. One randomised study on keratosis pilaris looked at the rough, bumpy texture often found on the upper arms. Over twelve weeks, a lactic acid cream and a salicylic acid cream both visibly smoothed the skin.

Start with the concern you notice most.

If your skin feels rough or looks dull, reach for an AHA. Glycolic acid gives the most noticeable smoothing. Lactic acid is the softer introduction.

If you are dealing with blackheads, a shiny T zone or pores that look congested by mid afternoon, reach for a BHA. Salicylic acid is the ingredient most consistently linked with clearer looking pores. If breakouts are part of the picture, our edit of cleansers for acne prone skin is a useful next read.

If breakouts and texture show up together, a formula with both acids saves you from layering two products.

Then decide on format, because it matters as much as the acid. A wash off exfoliant, such as a cleanser, sits on the skin for a minute before you rinse it away. That makes it the gentler choice for first timers and sensitive skin. A leave on exfoliant, such as a toner or pad, keeps working after application and has a stronger effect. Each suits a different skin and a different routine.

How often is the part people get wrong. There is no universal rule. Frequency depends on the specific formula and how your skin responds, so follow the guidance on the product and build up from there. For most leave on acids, a few evenings a week is a sensible beginning. Increase only if your skin stays comfortable.

One condition. If your skin is currently irritated, stinging, flaking or sunburnt, exfoliation is not the answer. Let it settle first with a routine built for redness and sensitive skin. Acid season will still be here.

“If it tingles, it is working.” A mild tingle can be normal on first use. Burning, lasting redness or tightness is your skin asking you to stop. Acids do not need to hurt to be effective.

“More acids, faster results.” Layering an AHA toner over a BHA serum under an exfoliating mask is the quickest route to a compromised skin barrier, the outer layer that keeps moisture in and irritants out. One exfoliant is enough.

“A scrub does the same job.” Grainy scrubs buff the surface by friction, which can be uneven and harsh on reactive skin. Acids work more evenly. BHA also reaches inside the pore, somewhere a scrub never can.

“Exfoliation is only for oily skin.” Dry skin benefits too, often from lactic acid, which exfoliates while helping skin hold on to water.

“SPF can take October off.” AHAs can increase the skin’s sensitivity to the sun. The US Food and Drug Administration advises daily sunscreen while using them and for a week afterwards. Irish autumn light is softer, not absent, which is why daily SPF stays in the routine throughout the year.

“You should see results after one use.” A smoother feel, yes. Visible change in texture and clarity takes consistent use over several weeks.

Acid season is not about doing more. It is about choosing well. Texture and dullness point to an AHA. Blackheads and oil point to a BHA. Both at once points to a formula that combines them. Start with one product, give it a few weeks of consistent use, wear SPF every day and let your skin tell you when it is ready for more. Or less.