Skin acids: A beginners guide on how to use them in your routine
You could say that acids are the Russell Brand of skincare. Hot, with a contingent of diehard fans, but undeniably complex when you look beyond the surface.
When used correctly, they can impart radiance and banish lines like no one’s business, but the term ‘acid’ can be a scary one, eliciting thoughts of biohazard warnings, even 20 plus years after the fact, Samantha Jones’ carpaccio look post-chemical peel – despite current products posing no such risks.
‘Acids are incredible ingredients that are extremely effective, and their effects can be seen very quickly on the skin,’ says Dan Isaacs, head of research and development at skincare brand Medik8. ‘You’ll see substantial changes in the skin’s texture in as little as a week, with results improving over time.’
From exfoliating AHAs, BHAs and PHAs to moisturising acids (hello, hyaluronic) and treatment acids that specifically target skin concerns, such as sun damage (think L-ascorbic acid, aka vitamin C), the dynasty is a prodigious one. Best, then, to swot up on the best acids in skincare – the good, the great and the trendy...
What are the best exfoliating skin acids?
Alpha-hydroxy acids (AHAs) are the holy grail for exfoliation, and there are four that you need to know about. While each of them works in the same way to exfoliate the skin, they all have individual superpowers. Which AHA will work best for you depends on your skin concerns and skin type.
‘AHAs are hydrophilic, “hydro” meaning water, and “philic” meaning loving,’ explains Victoria Hiscock, product specialist at AlumierMD. ‘It means that they interact with water molecules in the upper layers of the skin, which triggers a keratolytic (exfoliating) effect.’
The interaction between water and AHA dissolves the glue-like bonds that hold dead cells to the surface of your skin. Picture your skin as a brick wall. By loosening the cement in between the bricks (cells), it allows them to fall away more easily, revealing healthier and newer skin underneath. The new cells are able to reflect light (rather than absorb it like glow-robbing dead cells), giving you a radiant complexion. So, which AHA will work best for you?
Glycolic acid
The best acid for fine lines and wrinkles
Gycolic acid has the smallest molecules of all the AHAs, so penetrates the deepest and quickest. ‘Studies show that it helps to initiate collagen synthesis and boost hyaluronic acid (more on which later) in the lower skin layers, plumping fine lines and wrinkles,’ says Paula Begoun, dermatologist and founder of skincare brand Paula’s Choice.
Just FYI: Glycolic acid is so ruthlessly efficient that it only takes one application to yield results. The downside? It works so quickly that skin can become irritated. This is where percentages come in – the higher the strength, the more likely irritation will occur.
How to use glycolic acid: If you’re a glycolic virgin, start with formulations between 3% and 5%. ‘These will hit the sweet spot for daily use, because any irritation will be very minimal and will subside after a few applications,’ says Isaacs. ‘You’ll know, because the tingling sensation will disappear. However, be sure to give your skin regular breaks. So, use one bottle of product, then have a month off.’
Once your tolerance rises, you can move on to stronger formulas, around 10%. Anything higher should be used as a one-off treatment. It’s not just percentages that are key, pH levels are equally important. Some brands will formulate their glycolic acid with a high pH level to counteract potential irritation, but this also weakens the acid. (The higher the pH, the more alkaline something is; the lower, the more acidic it is.)
‘If you have a product with 5% glycolic acid, but a high pH level, it weakens the acid, lowering it to around 2%. The ideal pH level for glycolic should be three to four. This means the acid percentage stated on the label will be true to form. ‘pH levels aren’t always stated on the label, so check the website,’ suggests Isaacs.
Lactic acid
The best acid for dry skin
Remember the tale of Cleopatra bathing in milk? Well, she was way ahead of the game, because sour milk produces lactic acid. Now created synthetically in a lab, this AHA is gaining a following because its molecules are bigger than those in glycolic, so don’t penetrate as deeply to trigger that peeling action.
If you have dry or sensitive skin, this is a good thing. ‘At low percentages, around 5%, lactic acid also acts as a humectant, drawing moisture into the skin while it exfoliates,’ says facialist Kate Kerr.
Just FYI: It won’t provide dramatic overnight results on its own, so if you have a party, job interview or date for which you want instant results, opt for a formula that combines lactic with glycolic acid and plenty of antioxidants. This will still be weak enough not to cause irritation, but strong enough that you’ll notice a difference come morning.
In Sunday Riley Good Genes, £85, lactic and glycolic are combined with squalane to retexturise and hydrate.
How to use lactic acid: In the evenings after cleansing.
Mandelic acid
The best acid for pigmentation and acne
This is the newest AHA on the block. Research published in Dermatologic Surgery showed that it was as effective as glycolic at treating pigmentation from sun damage, but with less redness and irritation. And further studies show that it also reduces melasma by as much as 50% in four weeks.
Mandelic’s molecules are twice the size of glycolic’s and a third bigger than lactic’s, so irritation is reduced, as it takes a long time to penetrate the skin. But don’t be fooled by its softly-softly approach. Like other AHAs, mandelic’s micro-exfoliating properties help lift excess pigment from the skin’s surface.
However, it’s the only AHA to work in the skin’s deeper layers to inhibit melanin production. So what it might lack in speed, it makes up for in depth.
Just FYI: Its gentle approach also makes it a winner for those with darker skin tones, who need to be cautious in their approach to glycolic and lactic acids because the irritation they cause can lead to post-inflammatory hyperpigmentation if used incorrectly. ‘This is because melanin in the skin, which means there are also more melanocytes to react to irritation and trigger excess pigmentation,' adds Dija Ayodele, Founder of the Black Skin Directory.
If that wasn’t enough, it’s also being championed by cystic acne sufferers who are preaching its benefits on internet forums. ‘As well as exfoliating, it also has antibacterial properties, which help to regulate sebum production,’ says Dr Wei Chen, senior research and development manager at Dermatologic Cosmetic Laboratories. This stops acne forming. Products with 5% mandelic acid will be gentle enough for everyday use.
How to use mandelic acid: ‘If the formulation contains 10% mandelic acid, it should be applied two or three times a week, always in the evening,’ says Shabir Daya, co-founder of victoriahealth.com. That’s because AHAs increase your skin’s sensitivity, so you’ll also need to boost your UV protection with a good SPF.
Fears around AHAs aren’t totally misplaced. ‘I’ve seen a rise in patients coming to me with concerns about irritation from overusing or misusing acids,’ says Dr Sarah Shah, founder of the Artistry Clinic.
Her advice? If you haven’t used acids before, start by working one into your routine with a wash.’ Something like Peter Thomas Roth 3% Glycolic Solutions Cleanser, £36.60. ‘This limits the amount of contact time with your skin and avoids over-drying.’ Then you can move on to a serum or peel pads.
Just make sure you’re only using one acid based product in your regime. ‘You also don’t need to start on a single acid first [products containing a mix of acids are fine], but it’s beneficial to help you understand which ones work best on your skin,’ adds Isaacs.
Retinoic acid
The best acid for acne and wrinkles:
‘Retinol is a vitamin A derivative,’ explains Dr Rachael Eckel, cosmetic dermatologist. ‘When absorbed by cells, it turns into retinoic acid, which gets superb results on a multitude of skin issues. Think of any problem – wrinkles, texture, acne – and retinoic acid helps.’
We’re talking DNA level fine-tuning: ‘It strengthens your moisture-retaining lipid barrier, regulates pigment, exfoliates the epidermis and stimulates collagen and hyaluronic acid within the skin,’ says Dr Eckel. Research in the Journal of the American Academy of Dermatology showed it’s the only topical ingredient that can strengthen blood vessels, boosting flow to the skin’s surface.
Retinoic acid is prescription-only in the UK, but retinol, its less-irritating precursor, is widely available. Biochemically it does the same thing – just taking longer to get there. The downside? ‘Retinoids do incite reactions, which can be off-putting,’ says Dr Eckel. ‘Some peeling is expected, but it eases after two weeks.’
Just FYI: Keep it somewhere cool away from direct light; in combination, light and heat render retinol molecules biologically inactive and useless for the skin.
How to use retinoic acid: As a night treatment only. At-home products are available in strengths up to 0.5%. Start applying once a week, then build up to every night.
Salicylic acid
The best acid for oily skin and acne
It’s not just AHAs that will exfoliate your skin – salicylic is a beta-hydroxy acid (BHA), and it’s acne’s kryptonite. Unlike AHAs, it’s oil-soluble, meaning it can cut through excess oil on the skin’s surface.
Just FYI: ‘This doesn’t necessarily mean it reduces oily skin better than AHAs or PHAs (which we’ll get to), but it’s the only acid able to infiltrate the pore lining, so it can then flush out dirt, dead cells and trapped sebum,’ explains Begoun. This quickly restores oil flow out of the pore, so it’s less likely to get clogged with the debris that leads to blackheads, whiteheads and acne.
How to use salicylic acid: Strengths of 0.5% to 1% are usually gentle enough for use at home every day.
Polyhydroxy acids
The best acid for sensitive skin
Just as you’ve started to get a handle on understanding AHAs and BHAs, enter polyhydroxy acids (PHAs), which are being billed as new, but that’s not strictly true. The scientists who discovered them patented them in the 90s before marketing their own skincare ranges. This meant that other brands didn’t bother including PHAs as they were too expensive. Now the patents have expired, sparking a surge of products full of them, such as Medik8 Press and Glow Daily Exfoliating PHA Tonic.
PHAs’ large particle size means they take longer to penetrate the skin compared with AHAs, and they only work on the very top layer of the skin, without disturbing the delicate layers beneath. While they may not have the same deep-down exfoliating skills as AHAs, they boast other benefits.
Gluconolactone is the most powerful PHA – it’s also an antioxidant and a brilliant multitasker. Its properties protect skin from pollution and UV damage and, unlike AHAs, which can weaken the skin barrier, it actually helps to strengthen it, so skin is less likely to become inflamed by external and internal aggressors. A powerful humectant, it also ensures the skin stays well hydrated and impedes elastase, an enzyme that causes skin sagging. Skills, right? And wait, there’s more.
The other PHA, lactobionic acid, promotes skin firmness by stopping the degradation of collagen. And we’re still not done. Iron in the blood can be deposited in the cutaneous layer of skin, speeding up the ageing process.
Just FYI: PHAs bond with the iron in your skin, helping to banish this causal factor of ageing. But the biggest pull of PHAs is that they don’t increase photosensitivity, so your skin won’t become more vulnerable to sun damage, and they can be used on every skin type. PHAs don’t just exfoliate, they’re impressively reparative, too, which gives them an edge.
How to use PHAs: three times a week. Sweep over skin after cleansing and before moisturising.
What are the best moisturising acids?
Hyaluronic acid
The best acid for all skin types
Hyaluronic acid occurs naturally in the body and hydrates the skin by binding water to collagen. It’s a magnet for moisture, drawing it from the environment to keep cells plump and healthy. It can retain over a thousand times its weight in water within skin cells.
Adding it your skincare arsenal is paramount because, as you age, you naturally lose collagen and hyaluronic acid, so the skin becomes dehydrated more easily. Also, extreme weather and underlying skin conditions can cause tiny breaks in the protective skin barrier, allowing water to escape.
Just FYI: Look for products that boast HA in a 'low molecular weight' - that's how you know it has those easily absorbed small molecules.
How to use hyaluronic acid: In serums, mists (when applied on clean skin,) masks and moisturisers. Twice a day is a good shout;
What are the best treatment acids?
L-ascorbic acid
The best acid for free-radical damage
L-ascorbic acid (better known as vitamin C) is a potent antioxidant that wards off free-radical damage caused by environmental factors such as sun exposure and pollution. Percentages range from 10% to 20%, but the stability of the vitamin C within a formula is much more important than the percentage.
Just FYI: If vitamin C had a star sign, it would be Gemini, because it’s utterly two-sided. On one hand, L-ascorbic acid is the strongest form of vitamin C when it comes to dealing with sun damage and fine lines, yet, on the other, it’s also the weakest, because once it comes into contact with air and heat, it oxidises, rendering it useless. Therefore, a stable 5% vitamin C serum will be more effective than an unstable 25% serum.
So, how do you look for stable formulations? The packaging is key. AlumierMD EverActive C&E, £149, contains 15% L-ascorbic acid, stored in a separate cap above the serum. You only mix the concentrated vitamin C powder with the rest of the serum when you want to use it, ensuring its efficacy. Stable formulations won’t contain water, either.
How to use vitamin C: Apply your vitamin C serum in the AM day ideally before your moisturiser.
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