AHAs, BHAs, PHAs and beyond – we help you make sense of exfoliating acids for everything from skin brightening to pore shrinking and pigmentation busting. Plus how pick the right one for you
Chemical exfoliants, also known as ‘exfoliating acids’, are some of the most popular and most feared ingredients in skincare. We know they’re supposed to give you smooth, radiant skin – but chemicals? And acids? How are they not going to flay your face?
Rest assured, the word ‘chemical’ here does not mean that there are industrial chemicals in your skincare. It refers to the fact that these acids, which are often plant-derived, rta by the way, cause a mild chemical reaction in the skin, which is different to the way a face scrub (or ‘physical exfoliant’) removes dead cells by scraping them off.
How do exfoliating acids work?
Found in everything from spot creams to cleansers, toners, overnight skin treatments, scalp treatments, body care and even foot peels, these exfoliating acids do strip skin of a layer of dulling, clogging cells. “They work by dissolving the ‘cement’ that keeps dead cells sticking to the skin surface,” explains consultant dermatologist Dr Justine Kluk. But it is important to understand that your skin is itself mildly acidic; sweat and oil are full of acids, which help form a protective layer known as the acid mantle, keeping out against contaminants, bacteria and free radicals. So a well-balanced acid product is not going to burn holes in your face.
Cosmetic formulators go out of their way to create products that contain an effective yet non-irritating percentage of acids alongside the right pH level, as both these factors determine how aggressive (or not) your exfoliating acid is. This balance is a tricky thing to strike and should definitely be left to skincare scientists. One reason you’ve probably heard so many scare stories about acids leaving skin vulnerable and irritated is our over-enthusiasm in applying too many of them. Or our not sticking to the instructions, upsetting the balance and turning products that are meant only to remove dead cells into demons that melt living skin cells and destroy your skin barrier.
What are the benefits of chemical exfoliants?
Once you’ve decoded all the different names (from glycolic acid to lactobionic, AHAs to PHAs – don’t worry we’ve got you covered – read on) chemical exfoliants can be an essential part of everyone’s skincare routine, in the same way that SPF, vitamin C and a mild cleanser should be. Apart from getting rid of dullness and roughness, “they work at unblocking pores, and at reducing fine lines and wrinkles by increasing collagen density,” says Kluk. “These results tend to be cumulative, while the smoothing and brightening benefits are pleasingly immediate,” she adds. Acids can also act as humectants, binding water to the skin, and some even work as antioxidants.
To help you find a way through the maze of options, we’ve decoded the most popular acids and how to use them, alongside our pick of the best products for your skin type.
But let’s start with some general guidelines for how to get the most out of your exfoliating acids and how to slot them into your skincare routine.
What percentage exfoliating acid should you use?
We’ve all become a bit too obsessed with having high percentages of active ingredients in our skincare. When it comes to acids, high strength can lead to redness and irritation. But there’s another issue too. Brands can (and sometimes do) advertise very high level of acids, but then add so many neutralising agents to the formula that these acids can’t do much at all.
“How much of the acid actually penetrates the skin depends not just on the percentage of acid in the product but also in the pH value the product is formulated with,” explains cosmetic chemist Michelle Wong of Lab Muffin.
The result is a ‘gentler’ or ‘less effective’ (depending on your point of view) product than you bargained for. Overall, it’s far better to ignore percentages and focus on the types of acids that suits your skin best and the types of products that fit your lifestyle
How often should you use chemical exfoliants?
Not constantly, is the answer. How often you can safely use exfoliating acids depends on your skin type and circumstances, but a rule of thumb is not to do it more than twice or three times a week. Using them every day for long periods of time will over-strip even the sturdiest of skins; even though oily and ageing skins in particular need help with the natural skin-shedding process, we all need a certain level of oils and even dead cells to keep skin in balance. So don’t go acid-loopy, no matter how much you love that glow.
How many products with exfoliating acids can you use?
Cleansers, toners, masks, serums, moisturisers, even lip conditioners… any skincare product can have exfoliating acids as part of the mix these days, making it easy to overdose without knowing it. Overall, if a product advertises its exfoliating acid and bigs up its brightening benefits, you want that to be the only acid-containing product you use that day.
An exception can be to use a salicylic acid cleanser followed by a salicylic toner or spot treatment if you suffer from breakouts, although even then, you don’t want to use that combo for months on end. Or if you were to use a very gentle daily exfoliant such as a PHA toner, you could supplement that every now and then with a pre-event peeling mask or overnight acid serum. But in general, be as conservative as possible and don’t double, or even triple, up.
Where do chemical exfoliants fit into your routine?
In short, they go first once you’ve cleansed. Acids should be seen as the last step of your cleansing routine and/or the first one of your leave-on products. So: cleanser, acid, all other skincare.
Which chemical exfoliant or exfoliating acid is best?
There is no ‘best’ – every acid is different, as you’ll see below, and performs a slightly different task for the skin. It is much better to use a cocktail of acids than to stare yourself blind on whatever the most hyped or TikTok acid of the day is. “Acids have a wonderful synergistic effect, meaning they can enhance each other’s benefits and those for your skin if they are formulated cleverly together,” says doctor of dermopharmacy and Lixirskin founder Colette Haydon.
So an exfoliating acid product that boasts a blend of different acids is almost always your top choice, in the same way, that antioxidant or blends of peptide cocktails are more effective than single-ingredient serums of these actives.
Can skin get used to chemical exfoliants?
Yes, in a good way. Because exfoliating acids, if used conservatively, over time densify the skin and normalise the skin barrier, you skin will become less sensitive to them (if sensitive is how you started out) and you may, for instance, be able to tolerate a peeling mask where you never could before. Conversely, skin that may have needed strong acid products to put a dent in, for example, with acne, will over time need lower doses to achieve good results. Whatever your skin condition and chosen acid, however, start low and slow and build up.
How do I use chemical exfoliants safely?
Apart from heeding all of the above, always remember that, by exposing fresh new skin cells to the skin surface, you become more prone to burning and sun damage – so a daily broad-spectrum SPF50 is imperative for acid fans.
In addition, don’t be a smartarse and just stick to the instructions on your acid-containing product, whatever type it is. “The main thing is to use acids sensibly and not leaving them on longer or using them more frequently than instructed,” says cosmetic physician Dr David Jack. “I would also never use strong acids on broken skin or burns.”
Be very cautious combining them with potent cell-communicating ingredients such as retinol or ascorbic acid (vitamin C) as well, as the onslaught on your cells can soon get too much.
What is the right exfoliating acid for my skin?
To answer this question, it’s easiest to give you an overview of the most popular exfoliating acids and their uses. So here goes.
Alpha hydroxy acids or AHAs for smooth, even skin tone
These are the biggest group of chemical exfoliants, usually sourced from fruits and other botanicals. They are particularly helpful if you’re trying to create a more even skin tone and for refining your skin’s surface to make it smoother and more radiant. They function as humectants (attracting water) as well, helping to hydrate skin.
Here the main AHAs to know
Glycolic acid – the strong one for brightening
Derived from sugar cane, glycolic is the smallest acid molecule, which means it works fast but is also the most prone to causing irritation, as it can penetrate so well it sometimes doesn’t just loosen dead cells but tries to dislodge living ones as well. It’s why some call it ‘the sledgehammer of AHAs’. It’s found especially facial resurfacing treatments and body treatments.
Don’t overdo it, especially if you have thin, reactive or sensitised skin with conditions such as rosacea or eczema.
Lactic acid – the gentle one that’s good for sun damage and sensitive skins
Lactic acid, derived from milk, is naturally present in the skin which may help explain why it’s gentler on skin than glycolic acid, and more suited to sensitive skins. It has been shown to be more effective at helping clear up sun damage than glycolic is. It’s a particularly good humectant and it increases ceramides in the skin surface, helping to strengthen the barrier.
Mandelic acid – the gentler one for reactive, spot-prone and darker skins
Extracted from almonds, the mandelic acid molecule is quite a large molecule and therefore less irritating, so good for reactive and also spot prone skins (those with combination skin will love it). It has some antibacterial benefits. In professional peels, it gets a more even result than glycolic acid and poses less risk of post-inflammatory hyperpigmentation – so it’s more suited to dark skin tones than stronger AHAs.
Malic acid – the gentle one for dark spots and ceramide boosting
From unripe fruit such as sour apples, it boosts ceramide production and inhibits melanin production, reducing dark spots. It’s relatively gentle and is often used in acid products to boost the effects of other acids.
Citric acid – the go-easy one for pollution
As skincare expert Paula Begoun points out, this is technically lemon juice, which tips skin too far onto the acid pH spectrum and so causes sensitivity. But it does act as a chelator (a compound that binds heavy metals to it and removes them from your skin), nuking environmental pollutants. So, if you’re a city dweller, it’s a good addition to the mix in moderate doses.
Phytic acid for unclogging pores
Gentle and slow-release, this acid extracted from grains good at unclogging pores and blackheads and acts as a chelator as well
Azelaic acid – the delicate anti-inflammatory
Another grain-derived acid, it’s officially not an AHA, but it still functions as a leave-on exfoliant with strong anti-microbial and anti-inflammatory properties, making it a pro favourite for treating acne and rosacea in particular, as it delicately fights back both redness and oiliness.
Beta hydroxy acids or BHAs – for pore unblocking
Salicylic acid for pores and breakouts
This comes from willow or birch bark or wintergreen leaves, is the only BHA really used in cosmetics. Its USP is that it’s oil-soluble, which means it can go places AHAs can’t, namely the lining of your pores, where it effectively dissolves sebum alongside that ‘glue’ that keeps dead cells stuck both inside pores and on the skin surface. Salicylic acid is also anti-inflammatory and anti-bacterial, so it’s a superstar ingredient par excellence/for spot-prone skin. It’s not quite as gentle as azelaic acid, but it is generally well-tolerated, even by sensitive skins. Find it mainly in cleansers, toners and spot treatments as well as products to exfoliate a flaky scalp.
Polyhydroxy Acids (PHAs) non-irritating for reactive skins, good hydrators, suitable for ever day use
This is the most recent generation of acids. Larger in particle size that AHAs or BHA, they work in the skin’s top layers without disturbing the delicate deeper ones and cause little to know irritation, even if you use them every day. So, if your skin is reactive or sensitive, these are the acids to stick to.
They’re highly effective at increasing cell turnover and normalising the natural exfoliation process, though, and count as some of the most effective humectants in skincare, making them a popular addition to moisturisers. And there are a few other benefits as well…
Found naturally in the skin (like lactic acid), this PHA exfoliates, traps water, strengthens the skin barrier and has powerful, protective antioxidant benefits. It protects from UV damage as well as glycation (the stiffening of skin fibres caused by consuming too much sugar), so is a real anti-ageing molecule.
Bionic acids (lactobionic acid and maltobionic acid)
Derived from natural sugars, these gently exfoliate away at age spots, enlarged pores and deep lines, act as antioxidants (particularly targeting skin-degrading enzymes), humectants (hydrating skin; bionics are a top choice in moisturisers) and chelators (fighting off industrial pollutants).
Which acids aren’t exfoliating acids?
There are many acids in skincare that aren’t exfoliating acids at all, so they won’t remove any skin cells and, on the whole, pose no threat of irritation and in most cases can be used alongside your exfoliating acid. Here’s a (very) quick round-up.
Hyaluronic acid – the hydrator
Hyaluronic acid is a humectant naturally present in the skin; it famously holds 1000 times its weight in water to keep the skin surface hydrated. Despite its chemical name, it’s not remotely acidic and you can’t really use too much of it. Lately, it’s had some competition from polyglutamic acid, another non-acidic hydrator said to be three times more effective than hyaluronic.
L-Ascorbic acid – vitamin C
Pure vitamin C, this is very acidic, which you will notice when you put it on skin – it can bite for a while. But it’s not an exfoliating acid. It can temporarily sensitise skin, though, so if you are going into the summer sunshine with vitamin C, perhaps choose a non-acidic vitamin C compound such as THD ascorbate, and of course use a high SPF on top. Once absorbed, vitamin C is an excellent antioxidant that actually protects cells from sun damage, and boosts the protection you get from your SPF.
Retinoic acid – the age-proofer
The active compound in all retinoids (forms of vitamin A) including retinol, retinoic acid boosts collagen production and increases cell turnover, but it does it via a very different mechanism from exfoliating acids. Like exfoliating acids, it requires daily use of a high SPF to prevent fresh new baby cells from burning to oblivion as soon as they reach the skin surface. Because of the irritation potential, best err on the safe side and don’t use it at the same time as an exfoliating acid.
Amino acids – the peptide powerhouses
There are 20 different amino acids and they perform loads of essential functions in the skin, helping to hydrate, working as antioxidants, reducing signs of ageing, and more. Chains of them form peptides, which function as cell messengers, ‘telling’ the skin to do this or that. But amino acids don’t exfoliate and don’t irritate.
Essential fatty acids (EFAs) – the barrier builders
These lipids found in plant oils act as building blocks for skin cells, are an essential component of the protective skin barrier, smooth, soothe, nourish, moisturise and regulate oil production. Omega 9 (oleic acid) can have barrier-penetrating and exfoliating properties in high doses, but the other EFAs (omega 3 and 6, most commonly found in skincare) don’t. In fact, skin rich in EFAs is so resilient and healthy that it can better withstand exfoliation without experiencing any irritating side effects from it.
Tranexamic acid – the pigmentation buster
This minimises pigmentation but it’s not an exfoliating acid. It’s a ‘tyrosinase inhibitor’, which means it stops melanin - the brown pigment in your skin often caused by sun damage or spots - from coming to the surface and becoming visible as uneven dark marks. It’s also an anti-inflammatory.
The best chemical exfoliating products for face, whatever your skin type
Best chemical exfoliant for oily, congested skin: Trinny London Find Your Balance BHA Exfoliant, £36 for 75ml
High levels of salicylic and mandelic, plus oil-regulating botanicals and niacinamide, make this lightly vinegary-smelling leave-on serum the smart woman’s choice keeping for adult breakouts and oil slicks at bay.
Best chemical exfoliant for sensitive spot-prone skin: Paula’s Choice 10% Azelaic Acid Booster, £37 for 30ml
Azelaic acid is an anti-inflammatory, anti-oxidant, breakout buster, brown spot and redness reducer and gentle exfoliant. Combined with salicylic acid in this very light cream, you apply it alone or under moisturiser to settle breakouts without inflammation.
Best chemical exfoliant for combination skin: Dennis Gross Alpha Beta Ultra Gentle Daily Peel, £19 for 5
A gentle but pore-purging and hydration-boosting blend of lactic, mandelic and salicylic acid, these handy post-cleanse, single-dose wipes will keep your t-zone clear but your dry cheeks feeling comfortable.
Best chemical exfoliant for very dry skin: Neostrata Ultra Moisturising Face Cream, £35 for 40g
With 10% of the gentle, humectant polyhydroxy acid plus vitamin E and nourishing but light plant oils, this non-greasy cream, which you can use every day, delicately exfoliates and deeply hydrates at the same time.
Best chemical exfoliant for sun-damaged skin: Revolution x Sali Hughes Placid Five Acid Daily Exfoliant, £14 for 150ml
Here, glycolic acid peels roughened skin, tranexamic fades dark spots, lactic and malic brighten and hydrate, salicylic and phytic deal with congestion – this hard-working liquid toner (apply with a cotton pad) fights back all the scourges of sun damage. The odd smell is because it’s unscented – that’s a good thing.
Best chemical exfoliant for rosacea-prone skin: Willowberry PHA Liquid Exfoliator, £28.99 for 30ml
An unscented liquid serum that teams super-mild exfoliants and hydrators gluconolactone and lactobionic acid with pumpkin enzymes to gobble up dead cells, Pacman-like. There’s lots of humectants and soothing botanicals, too.
Best everyday chemical exfoliant: Wildsmith Time-release Pre-Serum Drops, £48 for 50ml
A ‘pre’serum because it goes on before all other skincare, these weightless, unscented drops have a micro-dosed blend of glycolic, lactic and malic acid gentle enough to use every day, plus encapsulated vitamin C to shield your face from environmental stressors.
Best chemical exfoliant for ageing skin: Ren Glycol Lactic Radiance Renewal Mask, was £40 now £26 for 50ml
Fruit-derived glycolic and lactic acids plus papaya enzymes in a juicy-smelling orange gel – leave it one for 30 minutes and even tired skin emerges soft, radiant and gleaming. With time and patience (use it once a week) it will plump out lines and minimise discolouration.
Best chemical exfoliant for dark skin tones: The Inkey List Mandelic Acid Treatment, £9.99
Formulated to tackle post-inflammatory hyperpigmentation (dark spots due to mild trauma like acne blemishes) without aggravating skin and risking more trauma, this scent-free, leave-on gel is quite safe for dark skins that need to keep inflammation at bay.
Best chemical exfoliant for teen skin: The Elements ABC Exfoliating Peel, £8
One to impress the chemistry teacher with, based as it is on the periodic table. This two-minute wash-off peel has salicylic and glycolic acid for intense pore-clearing, alongside charcoal for Hoovering out impurities. It tingles satisfyingly (always a winner for teens) but doesn’t irritate, acts fast and adds an element of fun by turning your pores black while it’s working (“cool”). Our editorial director’s 14-year-old son deems it a winner: it makes his pores look smaller. By the way, this works just as well on adult skin.