The Complete Guide to Types of Acids in Skincare: AHAs, BHAs, PHAs and More

If you have ever stood in a skincare aisle feeling genuinely baffled by the difference between glycolic and salicylic, or wondered whether AHA, BHA, and PHA are actually three separate things or just clever marketing, you are not alone. Skincare acids are one of the most genuinely effective ingredient categories available without a prescription - and also one of the most unnecessarily confusing. This guide exists to fix that.

First, a word on the word “acid” itself. It sounds alarming. It should not. The acids used in skincare are formulated at low concentrations, have decades of clinical research behind them, and are entirely safe when used correctly. The Glycolic Acid Toner from INKEY is £13. The PHA Toner is £13. The 10% Azelaic Acid Serum is £16. These are not aggressive, clinical-grade peels - they are well-formulated, accessible skincare products designed for everyday use at home.

What this guide covers: every major acid family you will encounter in skincare - Alpha Hydroxy Acids (AHAs), Beta Hydroxy Acids (BHAs), Polyhydroxy Acids (PHAs), hydrating acids, and specialty acids. For each one, you will find how it works, who it suits, how to use it safely, and which product to reach for based on your specific concern. If you want a broader foundation first, the Complete Skincare Routine Guide and the Complete Skincare Concerns Guide are useful companion reads.

Here is everything you need to know, broken down by acid type.

What Skincare Acids Actually Do - And Why They Work

To understand why skincare acids are so effective, it helps to understand what is happening on the surface of your skin at any given moment. Your skin is constantly renewing itself. Old, dead skin cells accumulate at the outermost layer - the stratum corneum - and naturally shed to reveal fresher cells beneath. This process is called desquamation, and when it works well, your skin looks bright, smooth, and even-toned.

The problem is that desquamation slows down. Significantly. With age, cumulative sun damage, hormonal fluctuations, and environmental stressors, dead skin cells begin to linger on the surface longer than they should. They build up, making the skin look dull and rough, clogging pores, and muting the light-reflective quality that makes skin look healthy. This is exactly where acids come in.

Skincare acids work by lowering the pH at the skin’s surface. This pH shift disrupts the bonds between dead skin cells - the same bonds that hold that outer layer stubbornly in place - and allows them to shed more efficiently. The result is accelerated desquamation: cleaner, smoother, brighter skin without the physical aggression of a scrub. And that distinction matters.

Chemical exfoliation is fundamentally more precise and consistent than physical exfoliation. A scrub, a muslin cloth, or a cleansing brush applies uneven mechanical pressure, creating micro-tears in the skin that can actually compromise the barrier over time - particularly in sensitive skin types. Acids, by contrast, dissolve the cellular bonds uniformly and selectively, acting on the dead surface layer without disturbing the living tissue underneath.

One of the most important concepts in understanding skincare acids is molecular size. It sounds technical, but the principle is straightforward: the smaller the acid molecule, the deeper it can penetrate into the skin, and therefore the more potent its effect. Glycolic acid has the smallest molecule in the AHA family, which is why it is the strongest and most effective - but also the most likely to cause irritation in sensitive skin. PHAs have the largest molecules of all exfoliating acid families, working closest to the surface with significantly lower irritation potential. Molecular size is not a flaw or a limitation - it is a feature. It is what allows you to match the right acid to the right skin type.

Concentration and pH work in tandem with molecular size to determine how powerful a product is in practice. A 10% glycolic acid toner formulated at a pH of 3.5 and used at home is a fundamentally different product from a 50% glycolic peel applied in a clinic. According to the FDA, over-the-counter AHA concentrations are established as safe for consumer use when formulated within recommended guidelines - a fact worth remembering when the word “acid” triggers unnecessary alarm.

There is one more critical distinction to establish before diving into individual acid families, and it is the point that most skincare guides miss entirely: not all skincare acids exfoliate. This is the key to understanding why this guide exists. Hyaluronic acid is a humectant that draws water into the skin. Tranexamic acid interrupts the melanin production pathway to reduce dark spots. Azelaic acid calms inflammation and redness. None of these exfoliate. Understanding which acids exfoliate and which perform entirely different functions is the entire point of what follows - and it is what will allow you to build a routine that actually addresses your real skin concerns. For more on how acids interact with other skincare ingredients, see our guide on what skincare ingredients you should not layer together.

Now that you understand what acids do and why they work, let us break down each acid family - starting with the most widely used: Alpha Hydroxy Acids.

Alpha Hydroxy Acids (AHAs) - Glycolic, Lactic and Mandelic Explained

Alpha Hydroxy Acids are water-soluble acids that work on the outermost surface of the skin by dissolving the bonds between dead skin cells. Because they are water-soluble, they do not penetrate into the pore lining - that is the job of BHAs, which we will come to shortly. What AHAs do exceptionally well is improve the look and feel of the skin’s surface: smoothing texture, brightening tone, improving light reflection, and over time reducing the visible signs of sun damage and early ageing.

The natural origins of AHAs are worth knowing because they are a useful way to remember what each one does. Glycolic acid is derived from sugarcane, lactic acid from milk, and mandelic acid from bitter almonds. All three are AHAs. All three exfoliate. But they differ meaningfully in molecule size, potency, and suitability for different skin types. If you are working on skin texture, our guide on how to improve skin texture is a useful companion read, and if you want a direct AHA-versus-BHA breakdown before going further, see our AHA vs BHA guide. Published research in cosmetics science has confirmed that AHAs measurably stimulate cell renewal and produce quantifiable improvements in texture, pigmentation, and fine lines with consistent use.

AHAs are generally best suited to normal, dry, dull, or sun-damaged skin. For oily or congested skin, they play a supporting role rather than leading it - that responsibility falls to BHAs. Within the AHA family, there are three key acids to know.

Glycolic Acid - The Most Potent AHA for Texture and Brightness

Glycolic acid has the smallest molecule of all AHAs, which means it penetrates most deeply and delivers the most potent exfoliating effect. The practical result of that potency is impressive: with consistent use, glycolic acid accelerates cell turnover, smooths rough skin texture, brightens an uneven complexion, refines the appearance of pores, reduces the visibility of blackheads at the surface, and - over weeks of regular use - visibly softens fine lines. It is the most results-driven of the AHA family.

Because of that potency, glycolic acid is best suited to normal, combination, and oily skin types. If your skin is on the sensitive side, starting with lactic or mandelic acid is the wiser first step.

The Glycolic Acid Toner (£13) contains 10% glycolic acid combined with 5% witch hazel. It is a no-rinse PM toner - apply after cleansing, leave it on, and follow with your moisturiser. Start at one to two times per week and build gradually as your skin adjusts.

For the body, the Glycolic Acid Exfoliating Body Stick (£15) applies the same exfoliating principle to keratosis pilaris bumps, ingrown hairs, and rough patches on arms, legs, and shoulders - with clinically proven results visible in as little as seven days.

One non-negotiable note: glycolic acid increases photosensitivity by removing the outermost layer of dead skin cells that would otherwise absorb some UV radiation. Use it in your evening routine only, and apply a broad-spectrum sunscreen every single morning - the Dewy Sunscreen SPF 30 is the daily essential to pair with it.

Lactic Acid - The Gentler Entry Point Into AHA Exfoliation

Lactic acid has a larger molecule than glycolic, which means it penetrates less deeply and acts more gently at the skin’s surface. For most people new to acids, this is the right starting point. It delivers the core AHA benefits - smoother texture, a brighter, more even complexion - while being significantly more tolerable for skin that has not built up a resistance to chemical exfoliation.

What sets lactic acid apart from other AHAs is its secondary function as a humectant. While it exfoliates, it simultaneously helps attract and retain moisture in the skin. This makes it uniquely suited to dry skin types, who might otherwise find even gentle exfoliation mildly dehydrating. If your skin is normal to dry and you are new to the world of acids, lactic acid is the logical and comfortable first step before progressing to glycolic.

Mandelic Acid - The Gentlest AHA With Dual Exfoliating and Antibacterial Action

Mandelic acid is the largest-molecule AHA, which makes it the gentlest of the three. It penetrates most slowly, produces the mildest exfoliating effect, and carries the lowest risk of irritation. For people with sensitive skin, reactive skin, or darker skin tones where there is a heightened risk of post-inflammatory hyperpigmentation from stronger actives, mandelic acid is the clear choice.

What makes mandelic acid genuinely interesting beyond its gentleness is its dual action: alongside surface exfoliation, it has documented antibacterial properties, making it a good option for those dealing with occasional blemishes alongside skin tone and texture concerns. The gradual exfoliation it provides improves tone and texture over time, and its antibacterial function makes it quietly effective on post-blemish marks without the intensity of a dedicated treatment acid.

The Mandelic Acid Treatment is the INKEY formulation for this acid - worth exploring if you fall into any of the groups above.

Quick reference - AHA comparison:

Glycolic acid: Smallest molecule, deepest penetration, highest potency. Best for normal, combination, oily skin. Key benefits: texture, brightness, pore refinement, fine lines.
Lactic acid: Medium molecule, moderate penetration, gentle + hydrating. Best for dry, normal, mildly sensitive skin or beginners. Key benefits: texture, tone, moisture.
Mandelic acid: Largest AHA molecule, slowest penetration, gentlest effect. Best for sensitive, darker skin tones, beginners. Key benefits: gentle exfoliation, antibacterial, tone and texture.

AHAs work on the surface - but if your concern is oiliness, congestion, or breakouts, you need an acid that can work inside the pore. That is exactly what Beta Hydroxy Acids do.

Beta Hydroxy Acids (BHAs) - How Salicylic and Succinic Acid Clear Congested Skin

The single most important thing to know about BHAs is this: they are oil-soluble. Every other significant difference between BHAs and AHAs flows from that one fact.

Because AHAs are water-soluble, they work on the skin’s surface. They dissolve in the water component of the skin’s environment and get to work on the outermost layer. BHAs, being oil-soluble, can dissolve in sebum - the natural oil your skin produces. This allows them to travel through the opening of the pore, penetrate the pore lining, and get to work dissolving the trapped combination of excess oil and dead skin cells that causes congestion, blackheads, and blemishes at its actual source. AHAs sweep the surface. BHAs go inside the pore.

Salicylic Acid - The Gold Standard for Oily and Congested Skin

Salicylic acid is derived from willow bark and has decades of dermatological use behind it. It is the primary and most well-researched BHA, and it is the acid of choice for anyone with oily, congested, or blemish-prone skin. To understand the full scope of what it does, see our complete ingredient guide: What is Salicylic Acid?

Its oil-solubility allows it to penetrate the pore lining and dissolve the trapped plug of sebum and dead skin cells at the root of blackheads and whiteheads. This is called keratolytic and comedolytic action - breaking down the keratin protein structure and dissolving the comedone (blocked pore). Beyond clearing existing congestion, salicylic acid has mild anti-inflammatory properties that calm the redness and irritation around blemishes, not just the blemish itself. It also has antibacterial properties that reduce the presence of blemish-causing bacteria in the pore environment.

The Salicylic Acid Cleanser (£12) contains 2% salicylic acid combined with 1% zinc and 0.5% allantoin. It is a rinse-off format, which makes it ideal for daily use in both AM and PM routines, and it works equally well on the chest, back, and shoulders for body blemishes. The Beta Hydroxy Acid (BHA) Serum (£10) is the leave-on counterpart - applied after cleansing, it works overnight for deeper pore exfoliation. Used together, these two products form one of the most effective congestion-clearing routines available at this price point. For how salicylic acid specifically targets blackheads, see our dedicated salicylic acid for blackheads guide.

Alongside salicylic acid, niacinamide is the other ingredient worth knowing for oily skin - it regulates sebum production and minimises pore appearance through a complementary mechanism. See What is Niacinamide? for the full ingredient breakdown on how these two work in combination.

Succinic Acid - A Gentler Option for Reactive or Blemish-Prone Skin

Succinic acid is technically classified as a dicarboxylic acid, but it functions in a way that is best understood alongside BHAs when considering its role in blemish-prone skin. It is gentler than salicylic acid, working primarily by calming inflammation, reducing redness, and helping to balance oil production rather than exfoliating aggressively inside the pore.

The Succinic Acid Treatment (£11) from INKEY includes 1% salicylic acid alongside succinic acid, delivering a dual-action effect - gentle enough for reactive skin, but not without targeted blemish benefit. It is an ideal option for those who want to address blemish-prone skin without the intensity of the full BHA Serum, or as an alternating treatment during the process of building tolerance to stronger exfoliating actives.

BHAs work deep inside the pore. But what if your skin is too sensitive for either AHAs or BHAs? That is exactly what PHAs were developed for.

Polyhydroxy Acids (PHAs) - Effective Exfoliation Without the Irritation

PHAs are the newest of the three main exfoliating acid families, and arguably the most misunderstood. The shorthand description - “a gentler version of AHAs” - is technically accurate, but it dramatically undersells what PHAs offer and why they exist as a distinct category. They are not a compromise. They are the correct tool for a specific group of skin types, and understanding them properly changes how you think about sensitive skin and exfoliation entirely.

The defining structural characteristic of PHAs is their large molecular size - the largest of all exfoliating acid families. Large molecules penetrate the skin slowly and shallowly, working closest to the outermost surface. This means PHAs exfoliate effectively without triggering the depth of cellular activity that can cause redness, stinging, or irritation in reactive skin. For anyone who has tried an AHA and found it too much, PHAs are not the fallback option - they are the right option.

What sets PHAs apart from other exfoliating acids entirely is their dual function. PHAs are also humectants. While they exfoliate, they simultaneously attract and retain moisture in the skin. For dry, dehydrated, or compromised-barrier skin types, this is not a minor detail - it is the difference between an exfoliant that depletes the skin and one that actively supports it. No other exfoliating acid family does both.

The primary PHA used in skincare is gluconolactone, derived from gluconic acid found naturally in honey, fruit, and wine. It delivers genuine surface exfoliation, improved texture, a brighter complexion, and a hydration boost - with minimal irritation potential. Clinical comparisons show PHAs offer surface exfoliation comparable to gentle AHAs like lactic acid, but with a significantly improved tolerance profile.

The PHA Toner (£13) contains 3% gluconolactone and can be used more frequently than stronger exfoliating acids - making it suitable as a near-daily gentle exfoliant for sensitive or dry skin types that cannot tolerate even weekly AHA use. It is one of the most accessible entry points to chemical exfoliation available.

For the body, the PHA Body Water Cream applies gluconolactone exfoliation in a hydrating cream format - ideal for sensitive body skin, dry patches, and anyone who wants the benefits of body exfoliation without any irritation risk.

AHA / BHA / PHA at a glance:

AHAs - Water-soluble. Surface exfoliation. Best for dullness, texture, uneven tone, dry or sun-damaged skin. Use 1-3x per week.
BHAs - Oil-soluble. Pore-penetrating. Best for oiliness, congestion, blackheads, blemishes. Use 1-3x per week.
PHAs - Large molecule. Surface exfoliation + humectant. Best for sensitive, dry, or reactive skin. Use more frequently; lower irritation threshold.

PHAs are not a consolation prize - they are the right tool for the right skin type. Beyond exfoliating acids, there are other acid types in skincare that serve very different purposes - from deep hydration to targeting hyperpigmentation and redness. Here is what you need to know.

Hydrating and Specialty Acids - Hyaluronic, Azelaic and Tranexamic Acid

Not every acid in a skincare routine is there to exfoliate. In fact, some of the most effective widely-used acid-type ingredients in modern skincare work through entirely different mechanisms - and many people using them do not even realise they are technically acids at all. Understanding these specialty acids is what separates a good routine from a genuinely optimised one.

Hydrate it: Hyaluronic Acid | Calm it: Azelaic Acid | Brighten it: Tranexamic Acid

Hyaluronic Acid - The Hydration Powerhouse Your Skin Already Makes

Hyaluronic acid does not exfoliate. Full stop. It belongs in the acid family by chemical classification, but its role in skincare is entirely about hydration. It is a humectant - a substance that attracts water molecules and binds them to whatever surface it is applied to. What makes hyaluronic acid remarkable is its capacity to hold up to 1,000 times its own weight in water. It is also naturally produced by the body, which is why the skin responds so well to it.

Applied topically, hyaluronic acid delivers immediate and lasting hydration, visibly plumps the skin, reduces the appearance of fine lines caused by dehydration (as opposed to structural ageing), supports the skin barrier, and improves the overall luminosity and feel of the skin. Multi-weight formulations - those containing hyaluronic acid molecules at different sizes - reach different depths within the skin’s layers, providing more comprehensive hydration than single-weight alternatives.

Hyaluronic acid suits every skin type without exception. And crucially, it can and should be used alongside exfoliating acids - applied first to damp skin to maximise water binding before your exfoliating serum or toner follows. For a deeper dive into how it works, see our full ingredient guide: What is Hyaluronic Acid?

The Hyaluronic Acid Serum (£16 for 60ml) contains 2% pure hyaluronic acid at three molecular weights, combined with Matrixyl 3000 peptide for an added anti-ageing dimension. Apply it to damp skin for the deepest possible moisture binding.

Azelaic Acid - For Redness, Post-Blemish Marks and Uneven Tone

Azelaic acid is a dicarboxylic acid with a genuinely impressive range of functions - and none of them are exfoliation. It inhibits the production of melanin (the pigment responsible for dark marks and uneven tone), calms the inflammatory responses that cause persistent redness and skin sensitivity, and has an antibacterial effect that makes it quietly effective on blemish-prone skin. It does three significant jobs simultaneously, which is why it earns its place in a wide range of skin concerns.

For a full breakdown of what azelaic acid does and how to use it, see our complete guide: What is Azelaic Acid?

What makes azelaic acid particularly valuable is its tolerance profile. It is one of the most well-tolerated actives available in skincare - suitable for sensitive skin, reactive skin, rosacea-prone skin, and darker skin tones where there is a heightened risk of further discolouration from stronger actives. It is also safe during pregnancy, though as always, checking with a medical professional is advised.

Unlike exfoliating acids, azelaic acid does not increase photosensitivity, which means it can be used in both AM and PM routines without any additional SPF concern beyond standard daily sun protection. It can also be used alongside retinol in a routine - see our guide on can you use azelaic acid with retinol for how to approach that combination. For those working on both skin tone and texture, our how to improve skin texture guide provides useful additional context.

The 10% Azelaic Acid Serum (£16) is a lightweight serum with an effective 10% concentration. It works progressively to calm persistent redness and fade post-blemish marks over consistent use.

Tranexamic Acid - The Targeted Brightening Acid for Uneven Tone

Tranexamic acid is a synthetic amino acid derivative and one of the most effective brightening ingredients in modern skincare. Like azelaic acid, it does not exfoliate. Instead, it works by interrupting the chemical communication pathway between keratinocytes (skin cells) and melanocytes (the cells responsible for producing pigment) - a pathway that, when disrupted by sun damage, hormonal changes, or post-blemish inflammation, leads to excess melanin production and the dark spots or patches that result.

For anyone with dark spots, hyperpigmentation, post-blemish marks, or uneven complexion caused by any of the above triggers, tranexamic acid addresses the issue at the source. It is particularly effective on melasma and post-inflammatory hyperpigmentation - two of the most stubborn pigmentation concerns. For a complete understanding of what hyperpigmentation is, how it forms, and the most effective ways to address it, see our guide: What is Hyperpigmentation?

Tranexamic acid is well-tolerated by sensitive skin and by darker skin tones, which makes it a more accessible alternative to some of the more aggressive brightening actives that carry a risk of further discolouration. For those dealing with both texture and pigmentation concerns simultaneously, alternating glycolic acid with tranexamic acid on different nights is an effective combination approach.

The Tranexamic Acid Serum (£16) is a targeted formula designed specifically for uneven tone, dark spots, and a dull or discoloured complexion. It is straightforward to integrate into an existing routine.

Now that you know what each acid does, the next question is how to actually start using them - especially if acids are new to your routine.

How to Add Acids to Your Skincare Routine Safely

Knowing which acid is right for you is only half the equation. How you introduce it matters just as much. Done thoughtfully, acids are some of the most rewarding ingredients in skincare. Done carelessly, they cause unnecessary irritation and put people off what could genuinely transform their skin. These five steps are how you do it right.

Step 1 - Start With One Acid and Give It Time

The single most common mistake people make when starting with acids is introducing too many actives at once. The logic feels sound - if one acid is good, two or three must be better - but in practice, it makes it impossible to know what is working, what is causing irritation, and what your skin actually needs.

Choose one acid that matches your primary skin concern. Use it consistently for a minimum of four to six weeks before introducing any additional active ingredient. Some people experience a temporary adjustment period in the first few weeks - skin may look slightly worse before it improves as the exfoliation process accelerates. This is sometimes called skin purging, and it is entirely different from a genuine reaction. Our complete guide to skin purging explains exactly what it looks like, why it happens, and when to be concerned versus when to persist.

Step 2 - Less Is More When You Begin

Start exfoliating acids - AHAs and BHAs - at one to two uses per week. If after two to four weeks your skin shows no adverse reaction (no persistent redness, no increased sensitivity, no disrupted barrier), you can begin building to three times per week.

The PHA Toner is the exception to this gradual frequency rule - its gentler nature allows more frequent use from early on, though starting slowly is still advisable for anyone with particularly reactive skin. Hydrating acids such as hyaluronic acid, and specialty acids such as azelaic acid and tranexamic acid, carry no exfoliation-related tolerance-building requirement and can generally be used daily from the outset.

Step 3 - Always Patch Test First

Before applying any new acid product to your full face, patch test it. Apply a small amount to the inside of your forearm or behind your ear and wait 24 to 72 hours. If there is no sign of irritation, persistent redness, or adverse reaction in that window, proceed to full-face use. This step is especially important for exfoliating acids. Learn exactly how to patch test and why it is a non-negotiable step in our dedicated guide: why do I need to do a patch test?

Step 4 - Get the Layering Order Right

The order in which you apply products in your routine significantly affects how well each one performs. As a rule, apply water-based serums from thinnest to thickest consistency. Hyaluronic acid applied to damp skin comes first - it creates a hydrated base that allows subsequent ingredients to absorb more effectively. Exfoliating acids follow. Moisturiser comes last to seal in everything applied before it.

Do not layer multiple exfoliating acids in the same routine. Using glycolic acid and salicylic acid together on the same evening dramatically increases the risk of over-exfoliation and barrier disruption. Alternating them on different nights is the correct approach - and this principle is actually the basis of a structured weekly practice known as skin cycling. Read our skin cycling guide for a practical breakdown of how to structure your week across different actives.

Exfoliating acids should also not be used in the same routine as retinol or vitamin C. These combinations are not dangerous, but they can cause unnecessary irritation and reduce the efficacy of both ingredients. Alternate them instead - see our guide on what not to mix with retinol for detailed guidance. For a full picture of what retinol is and how it fits into an acid-containing routine, see What is Retinol?, and for vitamin C layering guidance, see What is Vitamin C?. One useful note: azelaic acid and tranexamic acid are generally compatible with most other actives and carry fewer layering restrictions than exfoliating acids do.

Step 5 - Wear SPF Every Single Morning

This is non-negotiable. Exfoliating acids - particularly AHAs - increase your skin’s photosensitivity by removing the outermost dead cell layer that would otherwise absorb some UV radiation. Using glycolic acid at night without applying SPF the following morning actively undoes some of the benefit and increases your risk of sun damage and hyperpigmentation.

Use your exfoliating acids in your PM routine only. Then, every single morning without exception, apply a broad-spectrum SPF. The Dewy Sunscreen SPF 30 is the daily essential to pair with an acid routine - and for more on why SPF is particularly critical if pigmentation is one of your concerns, see our guide to SPF for hyperpigmentation.

PHAs, azelaic acid, tranexamic acid, and hyaluronic acid do not increase photosensitivity. But daily SPF is a non-negotiable skin health fundamental regardless - not just when using acids. For building these steps into a complete routine structure, the Complete Skincare Routine Guide is the place to go.

Which Acid Is Right for Your Skin Concern?

With the safety framework in place, here is a direct, concern-by-concern reference for matching the right acid to the right need.

Dull skin or uneven texture: Glycolic acid is your best-matched AHA for this. It accelerates cell turnover and smooths the surface more effectively than any other over-the-counter exfoliant. Start with the Glycolic Acid Toner(£13) two to three evenings per week.

Oily skin, congested pores or blackheads: This is BHA territory. Salicylic acid penetrates the pore lining and dissolves trapped sebum and dead skin cells at the source. The Salicylic Acid Cleanser (£12) for daily use and the Beta Hydroxy Acid (BHA) Serum (£10) for leave-on overnight exfoliation are the core pairing. Not sure whether you are dealing with blackheads or something that looks similar? See our guide: Sebaceous Filaments vs Blackheads.

Blemishes and breakouts: The Beta Hydroxy Acid (BHA) Serum (£10) and the 360 Skin Clearing Serum are the targeted options here. For a full breakdown of blemish and breakout types and causes, see our guide: Blemishes and Breakouts. If you are trying to understand the science of why breakouts happen, our guides on what is acne vulgarisand adult blemishes - why they happen are worth reading.

Sensitive skin or first-time acid use: Start with the PHA Toner (£13) for the gentlest effective exfoliation available, or the Mandelic Acid Treatment if you want the additional antibacterial benefit of a gentle AHA.

Dehydration or dryness: This is not an exfoliation concern - it is a hydration concern. The Hyaluronic Acid Serum(£16 for 60ml) is the direct answer.

Visible redness or redness-prone skin: Azelaic acid is the most targeted option for this. The 10% Azelaic Acid Serum(£16) works progressively to calm persistent redness and is one of the most well-tolerated actives for reactive skin.

Dark spots, hyperpigmentation or uneven tone: Tranexamic acid addresses the melanin production pathway directly. The Tranexamic Acid Serum (£16) is the targeted formula for this concern. For a deeper understanding of what causes hyperpigmentation and how to treat it comprehensively, see What is Hyperpigmentation?

Rough body skin, keratosis pilaris or ingrown hairs: The Glycolic Acid Exfoliating Body Stick (£15) is specifically developed for this - clinically proven results in seven days on KP bumps, ingrown hairs, and rough patches.

Early signs of ageing or fine lines: Glycolic acid used consistently is the most evidence-backed OTC option for improving skin texture and softening fine lines. For more significant anti-ageing results, pairing it with a Retinol Serumon alternate nights is a well-established approach. For full guidance on incorporating retinol alongside your acid routine, see What is Retinol?

One final reminder: do not try to address every concern simultaneously. Pick the one that matters most to you right now, build your routine around it, and give it genuine time to work. The Complete Skincare Concerns Guide is the place to go if you want help understanding and prioritising your full range of concerns.

You now know how to build your acid routine. Here are the most common questions answered, so you can get started with confidence.

Your Acids Questions, Answered

What is the best acid for beginners in skincare?

Mandelic acid or a PHA are the best starting points for most beginners. If your skin is sensitive or dry, the PHA Toner is the clearest first choice - effective exfoliation with the lowest possible irritation risk and the added benefit of hydration. If your skin is normal to combination and you want a gentle AHA with brightening and antibacterial benefits, mandelic acid is the better fit. Either way, start at one to two uses per week and build from there.

Can I use AHA and BHA together in the same routine?

It is best to alternate rather than layer them in the same routine. Using both an AHA and a BHA on the same evening significantly increases the risk of over-exfoliation and barrier disruption - even if neither acid feels strong on its own. Use your AHA on some nights and your BHA on others, and give your skin at least one or two nights per week with no exfoliating acids at all.

What does glycolic acid do for skin?

Glycolic acid exfoliates the surface of the skin by dissolving the bonds between dead skin cells, accelerating the natural process of cell turnover. The visible results of consistent use include smoother texture, a brighter and more even complexion, refined pore appearance, and a gradual reduction in the visibility of fine lines. It is the most potent AHA and works best for normal, combination, and oily skin types.

What does salicylic acid do for skin?

Salicylic acid is an oil-soluble BHA that penetrates the pore lining and dissolves the trapped combination of excess sebum and dead skin cells that causes congestion, blackheads, and blemishes. It unclogs pores, reduces blackhead visibility, calms the inflammation around blemishes, and has mild antibacterial properties that help reduce the skin environment in which blemishes form. It is the most effective over-the-counter acid for oily and congested skin.

What is the difference between AHA, BHA, and PHA?

AHAs are water-soluble acids that work on the skin’s surface - best for dullness, texture, uneven tone, and sun-damaged or dry skin. BHAs are oil-soluble acids that penetrate inside the pore - best for oiliness, congestion, blackheads, and blemishes. PHAs are the largest-molecule exfoliating acid family, working at the outermost surface with the added benefit of being humectants - best for sensitive, dry, or reactive skin types who need effective exfoliation without irritation risk.

When should I use acids in my skincare routine?

Most exfoliating acids - AHAs and BHAs - should be used in your PM routine only, because they increase photosensitivity and it is not appropriate to apply them before sun exposure. Apply after cleansing, before serums and moisturiser. PHAs can sometimes be used in the AM when followed by SPF, given their lower irritation profile. Hyaluronic acid, azelaic acid, and tranexamic acid can be used in both AM and PM routines without photosensitivity concern.

Can I use hyaluronic acid and glycolic acid together?

Yes - and this is actually a well-matched pairing. Apply hyaluronic acid first to damp skin, then follow with your glycolic acid product. The hyaluronic acid helps maintain hydration levels in the skin and can offset any mild dryness that glycolic exfoliation might otherwise cause. The two ingredients complement rather than conflict with each other.

What is azelaic acid good for?

Azelaic acid is best suited to reducing visible redness, fading post-blemish marks, and evening out an uneven skin tone. It has antibacterial properties and is one of the most well-tolerated actives available - making it suitable for sensitive, rosacea-prone, and darker skin tones. Unlike exfoliating acids, it does not increase photosensitivity and can be used in both morning and evening routines.

Do I need SPF when using acids?

Yes, without exception. Exfoliating acids - especially AHAs - increase UV sensitivity by removing the outermost dead cell layer that normally absorbs some sun exposure. Use exfoliating acids in your evening routine and apply a broad-spectrum SPF every morning, regardless of weather or season. The Dewy Sunscreen SPF 30 is the recommended daily SPF to pair with an acid routine.

With every question answered, here is the bottom line.

The Bottom Line on Skincare Acids

There is an acid for every skin concern. That is not a marketing claim - it is the practical reality of what this ingredient category, in its full breadth, actually delivers. From accelerating cell turnover and clearing congested pores to binding moisture, calming persistent redness, and interrupting the melanin pathways behind dark spots - acids are the most functionally diverse category in skincare.

The challenge has never been a lack of effective options. It has always been a lack of clear information. The word “acid” carries associations that do not belong in the context of a well-formulated skincare product, and that misplaced anxiety has kept too many people from ingredients that could genuinely transform how their skin looks and feels.

Once you understand how each acid works, who it is designed for, and how to use it safely, the decision becomes straightforward. You do not need a complicated ten-step acid routine. You need one well-chosen acid, used consistently and correctly, and enough patience to let it do what it is designed to do. That is what results actually look like - not complexity, but clarity.

If you are still unsure where to start, the askINKEY team is available to give personalised guidance based on your specific skin concerns. You do not have to work this out alone.