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The (Almost) A-Z Guide to All the Different Types of Skincare Acid

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When you think of the word acid in relation to skincare, it might seem a little scary. Acid on my skin? No thanks.

But before you take a giant leap backwards from your screen, don’t panic. Because the acids discussed in this article are the gentle kind. They’re the ones that- used properly- should only do good for the skin. The complexion do-gooders, if you will. 

So, whether it’s improving texture, increasing radiance or clearing up acne, AHAs, BHAs, LHAs and PHAs are here to help. And don’t worry, if all you just read was a load of letters, we will clear up what they mean too.

Here, you will be able to get a better idea of which acid is best for your skin, how each one works and how often you should use them.

With expert advice from world experts Dr Sonia Khorana, Akis Ntonos, Dr Geeta Yadav, Ian Michael Crumm, Dr Michele Green, Dr Beth Goldstein and Dr Tiina Meder, consider this article the Holy Grail in skincare acids. 

 

Image – Hannahcriswell/Stocksy

 


What exactly are AHAs, BHAs, LHAs and PHAs?

You’ve probably seen one or two of these written on skincare products either in shops, online or even in your collection at home. But if you’re thinking AH-ay?! Allow me to explain. 

AHA, BHA and PHA are umbrella acid categories. LHA is a single acid.  The last two letters of each of them stand for the same thing – hydroxy acid. The first letter is what differentiates them. 

  • AHA = Alpha Hydroxy Acid

“Water-soluble acids (like glycolic and lactic acids) used to exfoliate the skin’s surface, which is excellent for gentle skin refresh,” explains Ntonos.

  • BHA = Beta Hydroxy Acid

“Oil-soluble acids (like salicylic acid) that penetrate deeper into pores, making them ideal for oily and acne-prone skin.”

  •  PHA = Poly Hydroxy Acid

“Larger molecules than AHAs, providing gentler exfoliation,” he explains. “It is suitable for sensitive skin and offers additional antioxidant properties.”

  • LHA = Lipo Hydroxy Acid

“A derivative of salicylic acid, more lipophilic, works slower and is suitable for sensitive skin types,” he says.

 

Read on for the full details of the most popular types of acids, whether they’re right for you and what they can do for your skin!

 


Ascorbic acid

You might recognise this one better by its other name, vitamin C. “Ascorbic acid is the chemical name for vitamin C, a powerful antioxidant that helps neutralise the effects of harmful free radicals,” explains Dr Green

 

Image – Angelarober/Stocksy

What does it do?

“Ascorbic acid prevents UV damage from prematurely ageing skin and works to brighten areas of discolouration,” she continues. “Additionally, ascorbic acid promotes skin cell turnover and supports collagen synthesis to improve skin texture and tone.”

“It is best for reducing further damage, reduce abnormal pigmentation such as uneven skin tone and improve collagen production,” adds Dr Goldstein.

Who is ascorbic acid best for?

“It can be tolerated by most individuals although some formulations may be irritating as well as those mixed with fragrances may cause allergic reactions,” warns Dr Goldstein.  

Who shouldn’t use it?

Anyone prone to allergies or a reaction to strong fragrances.

How often should you use it?

“Usually, it is used in the morning underneath SPF products,” says Dr Goldstein.

 


Azelaic acid

Azelaic acid is a dicarboxylic acid found naturally in grains,” Ntonos explains. “It’s used to treat acne, rosacea and hyperpigmentation and has antibacterial, anti-inflammatory and keratolytic properties.”

 

Image – Guillefaingold/Stocksy

 

What does it do?

Oh-so much good stuff, starting with making the skin healthier. “Azelaic acid works to increase skin cell turnover, exfoliating dead skin cells to reveal healthy new cells that are more even in skin texture and tone,” explains Dr Green.

“It works to inhibit tyrosinase, an enzyme that controls melanin production, to minimize discoloration and inflammatory hyperpigmentation,” she adds.

“Additionally, azelaic acid carries antimicrobial and anti-inflammatory properties to regulate bacterial levels and reduce inflammation.”

Who is azelaic acid best for?

Everyone! “Especially those with skin conditions such as acne, hyperpigmentation and rosacea,” Dr Green says. I can personally vouch for the fact that, alongside a prescription of antibiotics, azelaic acid completely cleared up my acne after a year of major skin disruption. 

Who shouldn’t use it?

There’s good news there. “Azelaic acid is a gentle acid and can be used by all individuals, even those with sensitive skin,” says Dr Green

“Azelaic acid may exacerbate eczema symptoms, so it is important to perform patch tests and gradually increase usage, discontinuing if any irritation occurs.”

How often should you use it?

“Azelaic acid products can be used twice a day,” she says. “If you experience any irritation, it is best to decrease the frequency of usage to once daily or every other day.” 

I used mine in the morning and evening and made sure I wasn’t using any other acids in my skincare regime. If I did, my oily (sometimes sensitive) skin would itch. So, it’s best to make this your only acid at one time.

 


Citric acid

“Citric acid is an alpha hydroxy acid derived from (you guessed it!) citrus fruits,” explains Dr Yadav.

“It’s worth noting that citric acid appears in many skincare formulations and is often used to adjust a product’s pH. You’ll know if it’s being used as an AHA if it’s one of the first few ingredients on the ingredient list. When used as a pH stabilizer/adjuster, it’s used in very small amounts and found much lower on the ingredients list.”

 

Image – Hannahcriswell/Stocksy

What does it do?

“Alpha hydroxy acids like citric acid work by breaking down the bonds securing dead, dull skin cells to the skin’s surface, resurfacing the skin to reveal the fresh, bright skin underneath and promoting cellular turnover,” Dr Yadav says. “It is often used in cleansers and toners,” adds Dr Goldstein

Who is citric acid best for?

Anyone wanting more radiance, especially as they mature. “When used as an AHA, it can be a very effective exfoliant and is best for someone looking for an instant glow and wanting to stimulate cellular turnover, which slows as we age,” explains Dr Yadav.

Who shouldn’t use it?

It’s the usual story with AHAs. “Those with sensitive skin, particularly rosacea prone skin may want to avoid AHAs as they can be irritating,” Dr Yadav warns.

How often should you use it?

Dr Yadav says to go easy. “Chemical exfoliants are best used once or twice a week to minimise irritation,” she says. 

And Dr Goldstein agrees. “At high concentrations it can be irritating and cause burning, stinging and redness,” says Dr Goldstein. “It typically is not used daily unless the product has low concentrations.”

 


Ferulic acid

Here’s one for the organic lovers. “Though it may sound like an alpha hydroxy or beta hydroxy acid, ferulic acid is actually an antioxidant that’s derived from various, including nuts, fruits and seeds,” explains Dr Yadav.

 

Image – Annatabakova/Stocksy

What does it do?

As you go about your day, your skin is constantly being challenged by things like pollution and other bacteria. Ferulic acid is the great skin protector! 

“Antioxidants are free radical scavengers, meaning they neutralise free radicals emitted by environmental factors like pollution and UV and protect the skin against it,” Dr Yadav explains.

Who is ferulic acid best for?

As it turns out, everyone can benefit from a bit of ferulic acid. “Antioxidants like ferulic acid are important for nearly everyone to use on a daily basis as we’re constantly exposed to free radicals.”

Who shouldn’t use it?

“Antioxidants, especially in very high concentrations, can be irritating on easily sensitised skin, particularly those that are rosacea prone or eczema prone,” Dr Yadav. Feeling unsure? She suggests doing a patch test to “determine whether or not your skin can tolerate it before trying it on your face.”

How often should you use it?

Daily! “Apply it every morning, ideally in a formula that includes vitamin C and E, which all work synergistically to make the others more effective,” Dr Yadav says. 

But remember, it may protect from the effects of environmental factors but it’s not an SPF. “Using it under sunscreen is also critical – not only SPF is a must but pairing it with these ingredients can actually make them all stronger, including the sunscreen.”

 


Glycolic acid

Glycolic acid is an AHA. “It’s a chemical exfoliant and belongs to a family of naturally occurring ‘fruit acids’ called alpha hydroxy acids,” explains Dr Khorana. “It is considered the golden standard of AHAs.”

 

Image – Ohlamourstudio/Stocksy

What does it do?

First of all, it’s your dead skin cells’ worst enemy. “Glycolic acid works by gently dissolving the bonds between the dead skin cells on the skin’s surface which eventually shed/exfoliate and paves the way for newer/smoother skin underneath,” Dr Khorana explains.

It’s effective at fading hyperpigmentation. “It encourages skin cell turnover and exfoliates the pigmented skin revealing brighter skin making it a great ingredient for hyperpigmentation and discolouration,” she continues. 

“It also works to reduce the appearance of fine lines and wrinkles due to its exfoliating effect, which accelerates skin cell renewal and can help boost collagen.” Dr Khorana says it helps with breakouts as well. “Glycolic acid fights acne by exfoliating dead skin cells that can block pores.”

And finally, it can be great for moisture. “It’s classed as a humectant which means it draws moisture to your skin,” she adds. 

Who is glycolic acid best for?

“Glycolic acid can be used by any skin type, but its full benefits are most obvious in those with oily, dull, combination or ageing skin,” explains Dr Khorana.

Who shouldn’t use it?

“It may not be suitable for individuals with susceptible skin, eczema or rosacea as it can irritate,” warns Ntonos. “People with darker skin can still use glycolic acid but should be cautious with product overuse.”

How often should you use it?

According to Ntonos it depends on your skin type. “On average, starting with 1-2 times per week and slowly increasing until daily tolerance is achieved is recommended,” he says. “If the glycolic acid has a higher concentration, the product should be used less frequently and under the guidance of a skin expert or dermatologist.”

 


Hyaluronic acid

Hyaluronic acid is probably the acid you’ve heard the most about. “It is a natural substance produced by the human body with a unique capacity to retain water in tissues when it’s presented,” explains Dr Meder

“We have a lot of hyaluronic acid in our joints, connective tissues, eyes and skin. An average person has around 15 grams of it in their body, a third of which renews on a daily basis,” she continues.

 

Image – Ohlamourstudio/Stocksy

What does it do?

First and foremost, it’s a brilliant skin hydrator. “Like a hydration powerhouse, it is able to hold up to 1000 times its weight in water,” says Dr Meder. “When applied, it dives deep into your skin, hydrating and stimulating cell communication that helps to reduce fine lines and wrinkles while giving your skin a smooth, supple feel.”

It also helps to give your skin more ‘bounce’ too. “It’s an amazing collagen booster, which is the protein that gives your skin structure and elasticity,” she continues. “Hyaluronic acid jumps in to stimulate collagen bringing back firmness and helping your skin radiate that youthful glow.”

You could say hyaluronic acid is a bit of an over-achiever because it protects the skin from free radicals too. “It is an antioxidant superhero, battling skin-damaging free radicals and keeping your skin looking fresh and lively,” Dr Meder explains. 

“It is microbiome friendly, thriving while the skin surface is well hydrated as free water helps promote growth of good bacteria to maintain healthy skin,” she continues. “And finally, hyaluronic acid is a natural prebiotic that helps to soothe irritated skin, making it a must-have in skincare products such as face moisturisers or active serums.”

On a personal level, my skin has been transformed since using hyaluronic acid. It is smoother, my fine lines are definitely less visible and my skin usually feels moisturised and supple for the duration of the day.

Who is hyaluronic acid best for?

“Everyone, no exception,” she says. “HA is a universal ingredient, used largely in skincare, makeup and eye care products. It’s friendly to all skin types – sensitive, acne-prone, dry, mature, you name it!”

Who shouldn’t use it?

Honestly? There is no one who needs to avoid it. “It is light, non-greasy, and won’t clog pores or cause breakouts,” Dr Meder says. “It is truly a rare ingredient that has no side effects! Hyaluronic acid products are also absolutely safe to use in pregnancy.” Hallelujah! 

How often should you use it?

Because it’s so good for the skin and won’t irritate, you can use it twice a day.

 


Kojic acid

“Kojic acid is a skin-brightening ingredient derived from various species of fungi,” says Dr Green. “It is also a by-product of rice wine and fermented soy sauce.”

 

Image – Ohlamourstudio/Stocksy

What does it do?

“Kojic acid is a tyrosinase inhibitor and blocks the production of melanin to reduce hyperpigmentation from UV damage, melasma, and acne scars,” she continues. 

It also acts as an effective protective barrier for the skin. “It contains antioxidant properties to protect the skin from free radical damage caused by UV damage and environmental stressors.”

Who is kojic acid best for?

Anyone whose skin has been affected by the physical side effects from things like UV or acne. “Kojic acid is best for individuals looking to improve the appearance of discoloration from sun damage, melasma, and acne scarring,” explains Dr Green.

Who shouldn’t use it?

Similarly to azelaic acid, Dr Green says “all individuals generally tolerate kojic acid well, however, kojic acid products should be discontinued if any irritation occurs.”

How often should you use it?

“Kojic acid can be used twice daily in the morning and night,” she explains. But don’t forget your SPF. “Kojic acid should always be used with sunscreen in the daytime, as it can make the skin more sensitive to the sun. If irritation occurs, usage should be reduced.”

 


Lactic acid

“Lactic acid is from fermented fruits or milk and is classified as an alpha hydroxy acid, similar but less irritating than glycolic acid,” says Dr Goldstein.  

 

Image – Annatabakova/Stocksy

What does it do?

“Creams, lotions or other products with this ingredient can help with exfoliation and improvement of the structure of the top part of the epidermis, the stratum corneum, to improve retention of moisture by the skin as well as helping to remove dead skin cells,” she explains. 

“This can also assist with improving all over skin tone and texture with some boosting of collagen production.”

Who is lactic acid best for?

Lactic acid is less irritating than other acids as the molecular size is larger than other AHAs so it’s just right for sensitive skin types or anyone just starting out with chemical exfoliants. And because of its hydrating benefits, it’s particularly beneficial for dry skin types too.

Who shouldn’t use it?

Those with skin conditions like rosacea and eczema should check the concentration of their lactic acid before use, as anything over 5% can be too potent in these cases. Also, choose your timing wisely. “It can sting if applied to irritated skin or recently shaved skin,” warns Dr Goldstein.

How often should you use it?

“It can be used daily as a moisturizer,” she adds. If it’s higher in strength though, use it twice a week.

 


Lipohydroxy acid

“Lipohydroxy acid  – or LHA – is a derivative of salicylic acid,” explains Dr Meder. “What makes it unique is its ability to penetrate into the skin very slowly and stay active in the superficial layers of the skin for up to 4-5 days after one application.” 

 

Image – Ohlamourstudio/Stocksy

What does it do?

Being a derivative of salicylic acid, it helps to clear up acne and excess oil. “It is exfoliating and keratolytic, is able to speed up skin renewal, reduce comedones and thicken a skin structure via stimulating synthesis of collagen,” she says.

Who is lipohydroxy acid best for?

“It is best for people who are suffering from acne, for people who have oily skin that is prone to hyperkeratosis (rough skin) and for people with mature oily skin,” explains Dr Meder.

Who shouldn’t use it?

“I don’t recommend LHA based products to people with dry or sensitive skin, especially for older people with dry and thin skin.”

How often should you use it?

Dr Meder says to use it as a treatment first then apply it occasionally when the treatment has worked. “I suggest using it as an active course in acne treatment for a period of 10-12 weeks and [possibly] use it after treatment a couple of times a week to maintain healthy skin renewal.

 


Malic acid

Not to be confused with mandelic acid, “malic acid is an alpha hydroxy acid derived from apples,” says Dr Yadav. Who knew?!

 

Image – Juno/Stocksy

What does it do?

“It exfoliates the skin, aiding in dead skin cell remove,” says Crumm. “This can enhance skin texture and appearance, potentially improving self-tanning results.”

“Like citric acid, in lower concentrations, it can be used to adjust the pH of a skincare formula,” adds Dr Yadav

Who is malic acid best for?

“AHAs are best for someone looking to promote luminosity in their skin for a fresher, healthier-looking appearance,” she continues. Malic acid in particular is “ideal for those aiming to improve skin texture, reduce ageing signs and achieve a brighter complexion,” Crumm explains.

Who shouldn’t use it?

Watch out if you have sensitive skin. “Individuals with sensitive skin or conditions like eczema should avoid malic acid or use it cautiously,” he warns. “Always patch test and consult a professional.”

How often should you use it?

As always with acids, introduce it into your regime gradually. “Start with a lower concentration and less frequent application, such as once or twice a week, adjusting based on your skin’s reaction,” advises Crumm

 


Mandelic acid

Ntonos says mandelic acid is another AHA, derived from bitter almonds, and is one of the gentler acids. “It’s more prominent in molecular size compared to other AHAs which makes it penetrate the skin more slowly and less intensely, often resulting in less irritation overall,” he explains.

 

Image – Annatabakova/Stocksy

What does it do?

“It’s an exfoliant that helps accelerate cellular turnover of the skin,” Ntonos explains. “It can have a positive impact in reducing acne, fine lines and hyperpigmentation and improving skin texture.” So, similar to glycolic but works slower and much more gently.

Who is mandelic acid best for?

“This acid type is particularly beneficial for those with acne-prone, sensitive or darker skin tones due to its gentle nature and lower risk of irritation and hyperpigmentation,” Ntonos says.

Who shouldn’t use it?

Much like with glycolic acid, those with skin conditions like eczema and rosacea should avoid it. “Individuals with susceptible skin and specific allergies to almonds,” warns Ntonos

How often should you use it?

“Like glycolic acid start with 1-2 times per week, gradually increasing as tolerated,” he says. “The frequency can also depend on the product’s concentration.”

 


Salicylic acid

You may have heard of salicylic acid in relation to treating and clearing up acne. “It is the BHA hero,” Ntonos says. “Known for penetrating pores and dissolving sebum, making it highly effective for treating acne and blackheads.”

 

Image – Ohlamourstudio/Stocksy

What does it do?

Quite a lot as it happens. “Think about it as a mini facial,” Ntonos explains. “It exfoliates the skin, clears clogged pores, reduces sebum secretion and has anti-inflammatory properties.”

Who is salicylic acid best for?

You won’t be surprised to hear that those with oily, acne-prone skin can benefit the most from using salicylic acid. “It’s also practical for those dealing with blackheads and large pores.”

Who shouldn’t use it?

“People with dry, susceptible skin or those allergic to aspirin (as salicylic acid is similar to aspirin),” Ntonos warns. ‘Pregnant or breastfeeding women are often advised to use it cautiously.”

How often should you use it?

It’s best to wean your skin onto it. “Start with 1-2 times a week, gradually increasing as tolerated,” he recommends. “Overuse can lead to dryness and irritation, so listen to your skin, adjust accordingly and always follow the direction of your healthcare provider.”

Ntonos also reiterates the importance of sunscreen when using salicylic acid. “[Acids] can increase the skin’s sensitivity to the sun,” he says. “Additionally it’s always a good idea to patch-test new products and consult a healthcare provider first.”

 


The takeaway

As you can see there are *a lot* of acids to consider using to help improve your skin. But whatever your skin concern, there is an acid out there for you. 

Hyaluronic acid is the one everyone can use, with ‘no exception’, to quote Dr Meder. So, if you suffer from conditions like eczema or rosacea, hyaluronic is the safer acid for you. 

Wearing a daily SPF is crucial, but even more so if you are layering it over an acid. And remember that it’s usually a good idea to do a patch test before trying something new as well as introducing it gradually into your regime. 

 

Meet the experts

Dr Sonia Khorana is a GP with a special interest in dermatology, working as an aesthetic doctor, laser specialist and wellness & menopause lead. She is also the Dermatology Expert for Olay UK and Hero Cosmetics UK and a judge for this year‘s Glamour Beauty Power List Awards and Get The Gloss Beauty Awards.

 

Akis Ntonos is a dermatology nurse practitioner, injectable specialist, and co-founder of Aion Aesthetics, a premier New York aesthetic and injectable clinic.

 

Dr. Geeta Yadav is a board-certified dermatologist and founder of FACET Dermatology

 

Ian Michael Crumm is a celebrity aesthetican and beauty expert as well as co-host of the BeautyCurious podcast with Dr. Elyse Love. He is known for his passion for skincare and sun safety, is actively involved in philanthropic efforts to promote skin cancer awareness and believes that #ProtectedSkinWins.

 

Dr Michele Green is a New York-based, board-certified Cosmetic Dermatologist and the founder of MGSkinLabs.

 

Dr Beth Goldstein is a board-certified dermatologist and the co-founder of Modern Ritual

 

Dr Tiina Meder began her medical career in 1995 as a cardiologist specialising in treating pregnant women with heart conditions. Later on she switched to dermatology and in 2009 she launched her own brand, Meder Beauty, from her clinic in Antibes, France. 

 

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Beauty Editor

The former Beauty Editor of Glamour UK, Philippa has been a beauty and lifestyle journalist for over 16 years, picking up countless tips and tricks from makeup artists, hair stylists, dermatologists and celebrities. In that time she’s written for names like Cosmopolitan, The Sunday Times Style, The Telegraph, Grazia, Refinery 29 and Byrdie. Philippa lives in the UK with her husband, two children and their hyperactive cockapoo, Paddy.

Expertise: Makeup, hair care
Education: Oxford Brookes University
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