The verdict: BHA clears clogged pores, AHA polishes the surface

A clogged pore is a plug of sebum and dead skin cells sitting inside the follicle, below the surface. Anything that claims to clear it has to reach it down there, and that is where the chemistry settles the argument.

Salicylic acid, the BHA in almost every UK formula, is oil soluble. Rather than sitting on top of sebum it mixes with it, so a leave-on BHA can work its way into the pore lining, soften the plug from the inside and keep fresh oil flowing out instead of setting into new blackheads. Salicylic acid also has a mild calming effect on redness, which is one reason a well made 2% BHA suits more skin types than its strength suggests.

AHAs - glycolic, lactic and mandelic acid - are water soluble. They cannot follow oil into a pore, so they loosen the bonds holding dead cells to the surface and sweep away the outer layer. That improves how the pore opening sheds, but the plug underneath stays put.

• Pick BHA for: blackheads, whiteheads, congested T-zones, enlarged-looking pores, and oily or combination skin.
• Pick AHA for: rough texture, dullness, uneven tone and the marks spots leave behind.
• Typical UK strengths: leave-on BHA at 1 to 2%; leave-on AHA at 5 to 10%. Anything stronger belongs in a rinse-off weekly treatment.

If congestion is your main complaint, start with a 2% salicylic acid liquid exfoliant on two or three evenings a week. The leave-on liquid we have reviewed below targets blackheads and enlarged pores and is the format most people find easiest to stick with.

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What is actually blocking your pores

It helps to know what you are up against, because the different types of blockage respond at different speeds.

• Blackheads are open pores where the plug has oxidised on contact with air. The dark colour is oxidised oil, not dirt, which is why scrubbing at them achieves nothing.
• Whiteheads (closed comedones) are plugs the skin has sealed over: small, firm, flesh-coloured bumps, most common around the chin and jaw.
• General congestion is the rough, bumpy texture of pores part-filled with oil and dead cells, with nothing distinct enough to squeeze.
• Sebaceous filaments are the uniform grey dots across the nose that almost everyone has. They are normal structures, not blackheads, and no acid removes them permanently - a BHA just keeps them less noticeable.

The plugs themselves form when oil production outpaces the skin's ability to shed. Hormones and stress push sebum output up, dead cells linger longer as cell turnover slows with age, and leftover sunscreen or makeup adds to the mixture. Ingredient labels matter too: coconut oil, cocoa butter and isopropyl myristate are common pore-cloggers in richer creams, so check for a non-comedogenic label on anything that sits on your face all day.

UK conditions do their bit as well. Once the central heating goes on in October, indoor air dries the skin surface and many people's glands respond with more oil, which is why congestion often flares in winter rather than summer. In the hard water areas that cover much of southern and eastern England, cleansing can leave skin feeling tight and filmy, nudging the same oily rebound. And one myth to drop early: pore size is genetic. Nothing shrinks pores permanently - keeping them clear is what makes them look smaller.

Where AHA still earns its place

None of this makes AHAs pointless for congested skin. They solve different parts of the problem, and for some faces they are the better opening move.

• Glycolic acid has the smallest molecule of the common AHAs, so it penetrates the surface layers most effectively and has the strongest track record for smoothing texture and evening out tone.
• Lactic acid is larger and gentler, and it doubles as a humectant that helps skin hold on to water - useful when clogged patches sit on an otherwise dry face.
• Mandelic acid works slowest of all, which makes it the sensible pick for sensitive skin and for deeper skin tones, where irritation can leave pigmentation marks that outlast any spot.

Reach for an AHA first if your congestion is mild but your skin looks dull and feels rough, if old spot marks bother you more than new spots, or if dryness and flaking make a BHA feel too astringent. A 7% glycolic exfoliating toner - like the brightening and smoothing daily toner we have reviewed below - is a sensible home strength: enough to resurface properly, nowhere near professional peel territory.

There is an indirect pore benefit too. By clearing the dead-cell layer at the surface, an AHA keeps pore openings shedding as they should, so fewer new plugs get the chance to anchor. Think of it as maintenance for the top of the pore while a BHA deals with the depths.

Can you use AHA and BHA together?

Yes, and if you have both congestion and surface damage the combination covers ground neither manages alone. The mistake is using everything at once. Three approaches work, in ascending order of commitment:

1. One blended product. A formula pairing a modest AHA with a low-dose BHA gives you both actions in a single step, with less irritation risk than two separate strong products. The dual-textured exfoliating pads we have reviewed below combine 4.5% lactic acid with 0.45% salicylic acid for exactly this job, and a pre-soaked pad makes over-application harder.
2. Alternate evenings. BHA on Monday, a rest night on Tuesday, AHA on Wednesday, and so on. Simple to remember, easy on the barrier, and the pattern most combination skin settles into long term.
3. Split the day. Once your skin is trained, a BHA in the morning for oil control and an AHA at night while the skin repairs itself. Only attempt this after either acid alone causes no reaction.

What not to do: layer a strong AHA and a strong BHA in the same sitting, run acids on the same nights as a retinoid while you are still adjusting, or stack several salicylic products at once. A salicylic cleanser plus toner plus serum counts as three exfoliating steps, not one, and that is how tolerant skin gets talked into a flare-up.

A simple UK routine for clearer pores

Acids only deliver inside a routine that also removes the causes of congestion and protects the results. Evenings first:

1. Cleanse properly. A salicylic acid face wash - such as the pore-cleansing gel wash with niacinamide we have reviewed below - lifts oil and the day's grime without stripping. If you wear makeup or sunscreen, and you should, remove all of it: residue left on overnight is one of the most direct causes of blocked pores.
2. Exfoliate on a schedule, not on impulse. Apply your leave-on acid two or three evenings a week to begin with and build up only if your skin stays comfortable. Daily use is the ceiling, not the target, and chemical exfoliation more than once a day helps nobody.
3. Moisturise, even if you are oily. Freshly exfoliated skin loses water faster, and dehydrated skin compensates by producing more oil. An oil-free water gel moisturiser with hyaluronic acid - the one we have reviewed below is made for acne-prone and sensitive skin - replaces the moisture without adding grease.

In the morning: rinse or cleanse gently, moisturise, then apply SPF 30 or higher. AHAs in particular leave skin more sun-sensitive while you use them and for up to a week afterwards, and British cloud does not switch UV off - from spring through to October it is strong enough to re-darken the very marks you are trying to fade. A high-protection SPF 50+ facial sunscreen like the one we have reviewed below finishes the job properly.

One winter tweak: when the radiators come on, cut back acid nights before you cut back moisturiser, and consider a slightly richer (but still non-comedogenic) night cream from November to February.

Purging, irritation and when to get help

Any effective exfoliant can produce a rocky first month, and knowing the difference between purging and irritation stops you binning a product that is quietly working.

Purging happens because faster cell turnover pushes clogs that were already forming to the surface sooner. Expect a scatter of small whiteheads and blackheads in the areas where you usually break out, starting within the first fortnight and settling within about six weeks. Irritation looks different: stinging that lingers after application, burning, tight shiny redness, flaking, or spots appearing in places you never normally get them. That is your cue to halve the frequency or drop the strength, not to push through.

If you have overdone it - skin feels hot, looks glazed and reacts to everything - stop all acids, scrubs and retinoids for a week or two. Keep to a gentle cleanser, a plain moisturiser and sunscreen, and use a panthenol-based repairing balm - like the soothing one we have reviewed below - on the angriest patches until the barrier calms down. Reintroduce one acid at a lower frequency only once your skin feels normal again.

While you are clearing congestion, retire gritty nut-shell scrubs, keep to one salicylic product per routine and keep heavy balms and facial oils away from breakout-prone zones.

Finally, know the limits of exfoliating acids. Deep, painful spots, widespread inflamed acne or anything leaving scars needs more than a toner. A UK pharmacist can advise without an appointment, and the usual next step for inflamed spots is a 5% benzoyl peroxide gel - we have reviewed one below - used on alternate nights to your BHA rather than layered over it. See your GP if breakouts have not improved after eight to twelve weeks of consistent care, if they are scarring, or if they are getting you down day to day. Prescription options go well beyond anything on the high street shelf.