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A Definitive Guide To Skincare Acids

Read, bookmark and swot up for great skin.

Consider this your beauty periodic table or acid dictionary - whichever you’d prefer.

Azelaic, hyaluronic, glycolic, lactic, mandelic and salicylic... how well do you know your acids?

Sometimes it can seem more confusing than an advanced chemistry class, but there is good reason to proceed with caution when using acids on your skin. 

But all caution considered, it hasn't slowed the tide of all skincare brands delving into the trend and like all things in life, knowledge is power when it comes to choosing what's right for your skin.

Age of Acids 

While once, the concept of acid-on-skin might have sounded like something reserved for torture scenes, we can now barely talk skincare routines without a list of ingredients ending in ‘-ic’, all promising skin-wonders. 

Without doubt, skincare acids have a whole host of benefits and there is a one suited for everyone, depending on molecular size and strength.

However, they’re not all created equal; dosage, frequency of application, skincare concerns and layering practices are all key to achieving the best results, so using them can literally be an exact science.

We've broken down the bevvy of skincare acids on the market into an easy, understandable guide, so everyone can be an expert.

Scroll on to swat up on the acids most commonly found in skincare... 


First up, in alphabetical order, are Alpha Hydroxy Acids or AHAs.

AHAs can be either naturally occurring or synthetic and are arguably the most commonly used acids; glycolic, citric, mandelic, malic, tartaric and lactic.

As a group, they offer chemical exfoliation, removing dead cells and revealing a smoother skin surface. But not all of the acids within the water-soluble AHA family do the very same thing, nor should they be approached in a similar way.

Products with low AHA concentrations are typically gentle enough for at-home use, whilst chemical peels utilize concentrations of up to 70 per cent, under the supervision of a medical professional.

Glycolic acid is derived from sugar cane and is the smallest AHA molecule, which means it can penetrate deeper into the skin and can cause change (and irritation) fast as a result. When used correctly though, glycolic can even skin tone and soften the signs of ageing.

SHOP – 3% Glycolic Solutions Cleanser, €25,40, Peter Thomas Roth

Lactic acid (historically derived from milk, but now synthesized) has a much larger molecule and works to speed up cell turnover in a more stable manner, making it the acid of choice for reactive skins and for during pregnancy. It also has hydrating properties.

SHOP – Lactic Acid 10% + HA 2% Superficial Peeling Formulation, €6.95, The Ordinary

Malic acid lacks the exfoliating punch of glycolic and lactic acids, but it does pop up in brightening treatments, so if skin tone is one of your main concerns, it might be worth investigating. Mandelic acid is antibacterial and is effective in combating hyperpigmentation, especially melasma – pick one in an opaque container, as it is light-sensitive.


Moving on to beta hydroxy acids, or BHAs.

There is actually only one acid within this chemical class: salicylic acid, which is a derivative of aspirin. Like AHAs, salicylic acid is an exfoliant, often used to fight acne, thanks to its anti-inflammatory and anti-microbial properties. Derived from willow bark, it’s oil-soluble and can penetrate deep into sebaceous pores.

As well as treating existing blemishes, it helps to prevent future breakouts by neutralizing bacteria before it has the chance to develop into spots and can be useful in regulating sebum secretion.

Salicylic acid is also thought to manage keratosis pilaris (chicken skin) and ingrown hairs, both caused when dead cells aren’t exfoliated fully and a clogging of pores ensues. Due to its drying qualities, it’s best used on oilier skin and should be avoided if you’re allergic to aspirin or are pregnant.

SHOP – Hydrolat Anti Blemish Tonic, €70, 111 Skin @ Fetch Beauty 


While AHAs and BHAs are in countless skincare formulations, there’s a third, lesser-known acid group that’s recently seen a surge in popularity. Polyhydroxy acids or PHAs are being touted as the second coming of AHAs. If you’ve ever experienced an adverse acid reaction, have sensitive skin, eczema or rosacea, these are the liquid exfoliants you’ve been waiting for.

Two to look out for are lactobionic acid and gluconolactone, both offer slower penetration and a much gentler exfoliation. PHAs are also humectants, meaning they can retain moisture and hydrate the skin, and when used regularly, can strengthen barrier function, making the skin stronger over time, plus they don’t increase your skin’s sun sensitivity like AHAs do.

SHOP - Multi-Action Penta Peel, €74, DCL Skincare at Arnotts


Lastly: a word on hyaluronic acid (HA).

HA isn’t in the business of exfoliating or peeling. It is found naturally in the body, but our natural HA supplies dwindle as we get older, leaving skin drier and therefore more susceptible to showing signs of wear and tear.

It can absorb up to 1,000 times its own weight in water, and when a low molecular weight HA is applied to the skin, it can draw moisture up from the lower dermal layers to plump and give long-term hydration.

When applied at a high molecular weight, it creates a protective film that reduces the amount of water that evaporates from the skin, known as Trans Epidermal Water Loss (TEWL), which is regarded as one of the main causes of premature ageing.

SHOP - Hyaluronic Acid Intensifier, €92, SkinCeuticals

So, now you know! All that’s left is to go forth and reveal a fresh new face! 

Main image by @aabbeylee

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