Types of Acids in Skincare: AHA, BHA & PHA Guide

Skincare acids are one of the most effective and widely-used categories of active ingredients available - yet for most people, the world of acids feels unnecessarily confusing. Glycolic or salicylic? AHA or BHA? What even is a PHA? If you have stood in front of a shelf of toners and serums wondering which one is actually right for your skin, this guide is for you.

First, let’s address the obvious: the word “acid” sounds alarming. It conjures images of something harsh, clinical, or dangerous. In reality, skincare acids work at carefully calibrated low concentrations, and they are backed by decades of clinical research. Used correctly, they are some of the most transformative ingredients in any routine.

This guide covers everything - every major acid family including AHAs, BHAs, PHAs, hydrating acids, and specialty acids - along with how each one works, who it is best for, how to introduce it safely, and how to match it to your specific skin concern.

Our acid range spans everything from the bestselling Glycolic Acid Toner (£13) to the calming PHA Toner (£13) and the tone-evening 10% Azelaic Acid Serum (£16) - each one built around a specific skin concern, at a price that does not require justification. For guidance on building a full routine around acids, see our Complete Skincare Routine Guideand Complete Skincare Concerns Guide.

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

What Skincare Acids Actually Do - And Why They Work

Before diving into individual acids, it helps to understand what acids actually are in a skincare context - because not all of them do the same thing. The word “acid” is a broad chemical term, and in skincare it covers an extraordinarily diverse range of ingredients with very different mechanisms of action.

At the most basic level, what makes a substance an acid in skincare is its ability to lower the pH at the skin’s surface. For exfoliating acids - the most well-known category - this lowered pH is what allows them to loosen the bonds between dead skin cells. This process is called desquamation: the natural shedding of the outermost layer of skin. Normally, skin sheds dead cells on its own, but this process slows with age, sun damage, and hormonal fluctuations. Exfoliating acids accelerate it, helping the skin resurface more consistently and efficiently.

This is what distinguishes chemical exfoliation from physical exfoliation. Physical exfoliation - scrubs, brushes, textured cloths - works by physically abrading the skin’s surface to dislodge dead cells. It is blunt, difficult to control, and carries a real risk of micro-tears in the skin, particularly when used aggressively. Chemical exfoliation, by contrast, works at a molecular level. It is precise, consistent, and - when formulated correctly - significantly gentler on the skin’s barrier. For guidance on which ingredients work well alongside acids, see our guide on what skincare ingredients you should not layer together.

One of the most important concepts to understand when thinking about acids is molecular size. Different acids have different-sized molecules, which directly determines how deeply they penetrate the skin and how potent their effect is. Glycolic acid, the smallest AHA molecule, penetrates the deepest. PHAs, the largest exfoliating acid molecules, work closest to the surface. This is not a flaw - it is a feature, and it is why different acids suit different skin types and concerns.

Equally important is the concentration and pH of a formula. A higher concentration at a lower pH means a stronger, more aggressive action. This is why a professional chemical peel at 30-70% glycolic acid is an entirely different proposition from an over-the-counter toner at 10%. The FDA notes that AHAs have been studied extensively for their exfoliating properties - the clinical foundation for these ingredients is well-established, and the safety of over-the-counter concentrations is not a matter of debate.

Critically, not all skincare acids exfoliate. Hyaluronic acid is a humectant that hydrates. Tranexamic acid interrupts melanin production to fade dark spots. Azelaic acid reduces redness and calms inflammatory responses. Understanding these distinctions is the entire point of this guide - because choosing the wrong acid for your concern will not ruin your skin, but it will mean you are not getting the results you could be.

Used correctly and consistently, skincare acids are safe, effective, and suitable across virtually all skin types. The key word is “correctly” - and that is exactly what this guide is here to address.

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

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

AHAs are where most people begin their journey with skincare acids - and for good reason. This family of water-soluble acids has one of the strongest evidence bases in skincare, with decades of clinical research supporting their ability to improve skin texture, brightness, and tone. According to a clinical review published in the journal Cosmetics, topical AHAs stimulate skin cell renewal and produce measurable improvements in surface texture, pigmentation, and fine line appearance.

As a family, AHAs work on the skin’s surface. They dissolve the bonds between dead skin cells, allowing the outer layer of dull, built-up skin to shed more efficiently. The result is brighter, smoother skin that better reflects light - and over time, a more even, refined complexion. Most AHAs are derived from natural sources: glycolic from sugarcane, lactic from milk, mandelic from bitter almonds. They are best suited to normal, dry, dull, and sun-damaged skin types. Because they are water-soluble, they do not penetrate into pores - which is why someone with oily, congested skin may find them less transformative than a BHA.

If texture is your primary concern, our guide on how to improve skin texture covers this in further detail alongside the role AHAs play.

For a direct head-to-head comparison of how AHAs measure up against BHAs, see our AHA vs BHA breakdown.

Glycolic Acid - The Most Potent AHA

Glycolic acid is the most widely studied and most potent member of the AHA family, and its potency comes directly from its molecular size. It has the smallest molecule of all the AHAs, which means it penetrates more deeply into the skin than lactic or mandelic acid - making it faster-acting and more impactful, but also more likely to cause irritation in sensitive skin.

What does glycolic acid do? It accelerates cell turnover, dissolves the bonds between dead skin cells, and over time encourages the skin to produce fresh, renewed cells at a faster rate. The results are visible and wide-ranging: smoother texture, visibly brighter tone, refined pores, reduced appearance of blackheads, and - with consistent use - a measurable improvement in the look of fine lines and uneven pigmentation.

Glycolic acid is best suited to normal, combination, and oily skin types. If your skin leans sensitive or reactive, lactic or mandelic acid will serve you better.

Our Glycolic Acid Toner (£13) delivers 10% glycolic acid alongside 5% witch hazel - a no-rinse toner applied after cleansing in your PM routine, one to three times per week. It is one of the most straightforward ways to introduce glycolic acid without needing to redesign your entire routine.

Glycolic acid is not only for the face. If rough body skin, keratosis pilaris (KP) bumps, or ingrown hairs are a concern, our Glycolic Acid Exfoliating Body Stick (£15) is clinically proven to tackle these concerns in as little as seven days - applied directly to dry skin on the arms, legs, or anywhere KP is present.

One non-negotiable when using glycolic acid: SPF the morning after. Glycolic acid increases photosensitivity by removing the outermost dead skin cell layer that provides a minimal natural barrier to UV exposure. Always follow with a broad-spectrum SPF - our Dewy Sunscreen SPF 30 is an excellent daily option.

Lactic Acid - The Gentler Entry Point

Lactic acid has a larger molecule than glycolic acid, which means it penetrates the skin less deeply and acts more gently - making it the preferred starting point for those new to AHAs, or those with slightly more sensitive skin.

Its benefits are similar to glycolic but more subtle in pace: smoother surface texture, a brighter, more even tone, and improved hydration - because lactic acid has humectant properties alongside its exfoliating action. It attracts water molecules to the skin as it exfoliates, which makes it uniquely kind to those who find pure exfoliating acids drying.

Lactic acid is best for dry, normal, or mildly sensitive skin types, and is often the first AHA recommended to anyone who wants to start with acids but is unsure how their skin will respond. If you are new to chemical exfoliation, lactic acid is the logical first step in the AHA family before progressing to glycolic acid.

Mandelic Acid - The Gentlest AHA With Dual Action

Mandelic acid is the largest-molecule AHA - and therefore the gentlest. It penetrates the skin the most slowly of the three, producing a mild but consistent exfoliating effect with the lowest risk of irritation or redness.

What makes mandelic acid particularly notable is its dual action: alongside surface exfoliation, it has antibacterial properties, which gives it relevance not just for dull or uneven skin but for those with occasional blemishes. It is one of the few AHAs that is routinely recommended for sensitive skin and for darker skin tones - where stronger AHAs like glycolic carry a higher risk of triggering post-inflammatory hyperpigmentation (PIH) if they cause irritation.

Benefits include gentle surface exfoliation, improvement in skin tone and texture, and a gradual reduction in the appearance of post-blemish marks. It is the ideal AHA for anyone who wants to start exfoliating but has concerns about sensitivity or skin tone.

Our Mandelic Acid Treatment delivers all of these benefits in a targeted, easy-to-use format.

A quick guide to the AHA family:

Glycolic acid - smallest molecule, deepest penetration, highest potency. Best for normal to oily, experienced acid users. Key benefits: texture, brightness, pore refinement, fine lines.
Lactic acid - mid-size molecule, gentler action, added hydration. Best for dry or mildly sensitive skin, beginners. Key benefits: smooth texture, even tone, hydration.
Mandelic acid - largest AHA molecule, slowest penetration, gentlest action. Best for sensitive skin, darker skin tones, beginners, blemish-prone. Key benefits: gentle exfoliation, tone, antibacterial.

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 what Beta Hydroxy Acids do.

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

If AHAs are the brightening acids, BHAs are the clearing acids. The fundamental difference between the two families comes down to one word: solubility. AHAs are water-soluble. BHAs are oil-soluble - and that distinction changes everything.

Because BHAs can dissolve in oil, they are able to penetrate through the sebum sitting inside pores, reaching the pore lining itself. While AHAs sweep the surface of the skin, BHAs go deeper - exfoliating from within the pore to dissolve the trapped oil, dead skin cells, and debris that cause congestion, blackheads, and blemishes. According to the FDA, beta hydroxy acids have been widely studied for their ability to penetrate oily skin and exfoliate within the pore - making them the clinical standard for oily and congestion-prone skin types.

BHA vs AHA - the key differences at a glance:

AHAs work at the surface - best for dullness, texture, pigmentation
BHAs work inside the pore - best for oiliness, congestion, blackheads, blemishes
AHAs are water-soluble - suited to normal, dry, and surface-concern skin
BHAs are oil-soluble - suited to oily, combination, and blemish-prone skin

Salicylic Acid - The Gold Standard for Oily and Congested Skin

Salicylic acid is the most widely used BHA in skincare, and it has one of the strongest track records of any active ingredient in the category. Derived from willow bark, it has been used in dermatology for decades - long before it became a fixture in high-street skincare.

Its mechanism is precise: salicylic acid penetrates into the pore lining, where it dissolves excess sebum and dead skin cells that have become trapped. This directly unclogs pores, reduces the appearance of blackheads, controls excess oil production at the surface, and - with consistent use - helps to prevent new blemishes and breakouts from forming.

What does salicylic acid do beyond clearing pores? It also has mild anti-inflammatory properties, which means it can help to calm the redness and irritation that often accompanies breakouts, not just the breakouts themselves. It is, quite simply, the most effective acid for oily and congested skin.

INKEY offers two ways to use salicylic acid, depending on your routine and the level of action you want. Our Salicylic Acid Cleanser (£12) delivers 2% salicylic acid alongside 1% zinc - an active first or second cleanse that you rinse off, making it a low-commitment, high-frequency option. It can also be used on the chest, back, and décolletage - particularly useful for body breakouts. For more targeted, leave-on action, our Beta Hydroxy Acid (BHA) Serum (£10) sits in the routine after cleansing and works continuously while the skin rests overnight. When used together, they form one of the most effective congestion-clearing routines available at this price point.

Succinic Acid - A Gentler Option for Reactive Skin

Not everyone’s skin can tolerate salicylic acid at full strength - particularly those with reactive, easily-irritated skin who still deal with occasional blemishes or oiliness. This is where succinic acid becomes relevant.

Technically a dicarboxylic acid, succinic acid is often grouped alongside BHAs because of how it functions on blemish-prone skin. It is gentler than salicylic acid, working primarily by calming inflammation, reducing redness around blemishes, and helping to balance oil production at the surface. INKEY’s formulation also includes 1% salicylic acid, giving it a dual-action edge without the full intensity of a dedicated salicylic acid product.

Our Succinic Acid Treatment (£11) is the ideal choice for those who want targeted blemish support without the risk of over-exfoliation - or as a complementary product to alternate with the BHA serum for those who want to build tolerance gradually.

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 they are arguably the most misunderstood. They are frequently described as “the gentle version of AHAs” - which is technically accurate, but undersells what makes them genuinely useful in their own right.

Polyhydroxy acids have the largest molecule size of all the exfoliating acid families. This large molecular size means they penetrate the skin more slowly and work closer to the surface than AHAs or BHAs - producing effective exfoliation with significantly lower irritation potential. For anyone who has tried glycolic or salicylic acid and experienced redness, stinging, or peeling, PHAs offer a way to exfoliate without triggering the same response.

But what truly distinguishes PHAs is their secondary function: they are also humectants. Unlike AHAs or BHAs, PHAs attract and retain moisture in the skin as they exfoliate - meaning they can improve skin texture and brightness without compromising hydration or the skin barrier. For dry, dehydrated, or compromised-barrier skin types, this is not a minor detail. It is a meaningful clinical difference.

The primary PHA used in skincare is gluconolactone - a polyhydroxy acid derived from gluconic acid, which occurs naturally in honey, fruit, and wine. It provides gentle surface exfoliation, improved skin texture, a brighter complexion, and a hydration boost - all with minimal risk of irritation or sensitivity.

PHAs offer comparable surface exfoliation to gentle AHAs like lactic acid, but with significantly lower irritation potential - making them the ideal first step for anyone who has found AHAs too strong.

Our Glycolic Acid Toner page itself recommends the PHA Toner as the alternative for sensitive skin - a direct, substantiated recommendation that speaks to how clearly differentiated these two products are. Our PHA Toner (£13) delivers 3% gluconolactone and can be used more frequently than most exfoliating acids - making it ideal as a near-daily gentle exfoliant for those who want consistent results without the recovery time that higher-strength acids can require.

PHAs are also well-suited to body use. For sensitive body skin, dry patches, or anyone wanting to exfoliate without risk of irritation, our PHA Body Water Cream brings the same gluconolactone exfoliation to the body in a hydrating cream format.

AHA, BHA, and PHA - the complete picture:

AHA - water-soluble, surface exfoliation, moderate penetration. Best for: normal, dry, dull, sun-damaged skin. Sensitivity: moderate.
BHA - oil-soluble, penetrates pores, deeper action. Best for: oily, combination, congested, blemish-prone skin. Sensitivity: low-moderate.
PHA - large molecule, surface exfoliation, hydrating. Best for: sensitive, dry, reactive, beginners. Sensitivity: very low.

PHAs are not a compromise - 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 your skincare routine is there to exfoliate. Some of the most effective and widely-used acid-type ingredients in modern skincare work by entirely different mechanisms - hydrating, brightening, calming, and targeting specific skin concerns that exfoliating acids simply cannot address. Understanding these specialty acids is what separates a good skincare routine from a great one.

Hyaluronic Acid - The Hydration Powerhouse

Let’s start with the most well-known: hyaluronic acid. It does not exfoliate. Full stop. Hyaluronic acid is a humectant - a substance that works by attracting water molecules and binding them to the skin. It is a naturally occurring substance in the body, found in the connective tissues, eyes, and skin, and it is capable of holding up to 1,000 times its own weight in water.

In skincare, hyaluronic acid delivers immediate and lasting hydration, plumping the skin and reducing the visible appearance of fine lines caused by dehydration. Over time, consistent use supports the skin barrier, improves the overall feel and texture of skin, and creates a more luminous, healthy complexion. It is effective at different depths depending on molecular weight - multi-weight hyaluronic acid can reach multiple layers of the skin for a more comprehensive hydrating effect.

Hyaluronic acid is suitable for all skin types without exception. It can - and should - be used alongside exfoliating acids: apply it first to damp skin to maximise water binding, then follow with your AHA, BHA, or PHA step. This combination keeps the skin’s hydration levels stable while exfoliating acids do their work.

Our Hyaluronic Acid Serum (£16 for 60ml) delivers 2% pure hyaluronic acid at three molecular weights, alongside Matrixyl 3000 - one of the most well-studied peptide complexes for supporting skin firmness. Applied to damp skin for deepest penetration, it is one of the simplest and most universally beneficial additions to any routine.

Azelaic Acid - For Redness, Blemish Marks and Uneven Tone

Azelaic acid is a dicarboxylic acid with a genuinely impressive range of functions - and yet it remains one of the most under-discussed actives in mainstream skincare. It works by inhibiting melanin production (the process that creates dark marks and uneven pigmentation), by calming the inflammatory responses that cause redness and sensitivity, and by exerting antibacterial effects on blemish-prone skin. The result is an acid that targets redness, post-blemish marks, and uneven tone simultaneously - without exfoliating.

What is azelaic acid good for? Primarily: visible redness, post-blemish marks, uneven skin tone, and reactive or rosacea-prone skin. It is one of the most well-tolerated actives available - genuinely suitable for sensitive skin, and considered safe during pregnancy (though as always, we recommend checking with your doctor before using any active ingredient during pregnancy).

Unlike AHAs and BHAs, azelaic acid does not increase photosensitivity, which means it can be used in both your AM and PM routine. Apply it after cleansing and before your moisturiser.

Our 10% Azelaic Acid Serum (£16) delivers an effective 10% concentration in a lightweight serum format - a meaningful dose that works progressively to calm redness and fade the appearance of post-blemish marks with consistent use. For skin texture improvement alongside tone correction, also see our guide on how to improve skin texture.

Tranexamic Acid - The Targeted Brightening Acid

Tranexamic acid is a synthetic amino acid derivative that has emerged as one of the most effective brightening ingredients in skincare - particularly for stubborn, hard-to-shift pigmentation. It does not exfoliate. Instead, it works by interrupting the communication pathway between skin cells that triggers excess melanin production - the process responsible for dark spots, hyperpigmentation, and the uneven tone that follows breakouts, sun exposure, or hormonal changes.

What does tranexamic acid do in skincare? It visibly fades dark spots and areas of hyperpigmentation, evens out skin tone, and brightens a dull or discoloured complexion over time. It is particularly effective on melasma and post-inflammatory hyperpigmentation - and crucially, it is well-tolerated by sensitive and darker skin tones, where some brightening ingredients carry a risk of further discolouration if they cause irritation.

Tranexamic acid can be used alongside AHAs: for those dealing with both texture and pigmentation, alternating glycolic acid with tranexamic acid on different nights is an effective combination approach.

Our Tranexamic Acid Serum (£16) delivers a targeted, results-focused formula for anyone whose primary concern is uneven tone, dark spots, or a dull, uneven complexion.

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

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

One of the biggest mistakes people make with skincare acids is not that they use them - it is that they use them too quickly, too often, or in the wrong combination. Acids are genuinely effective, but they are also active ingredients, which means they require a degree of intention when introducing them. Here is a straightforward, practical guide to doing it right.

Step 1 - Start With One Acid

Before anything else: choose one acid that matches your primary skin concern, and start there. Introducing multiple acids at once - or piling an AHA, a BHA, and a vitamin C serum into the same week - is one of the fastest ways to disrupt your skin barrier and end up with more sensitivity than you started with.

Give your skin a minimum of four to six weeks to adjust to a new acid before introducing another active. Your skin needs time to build tolerance, and the results you are looking for take consistency, not complexity.

Step 2 - Less Is More at the Beginning

Start exfoliating acids - AHAs and BHAs - at one to two times per week. After two to four weeks with no adverse reaction, you can gradually increase to three times per week based on your skin’s tolerance. Do not rush this. Skin that adapts slowly to acids is more likely to show sustained results without barrier disruption.

The PHA Toner is an exception - its gentler nature means it can be used more frequently from the start, though we still recommend beginning slowly. Hydrating acids (hyaluronic acid) and specialty acids (azelaic acid, tranexamic acid) do not exfoliate, so they can generally be used daily from the beginning without issue.

Step 3 - Always Patch Test First

Before committing any new acid product to your full face routine, patch test. Apply a small amount to the inside of your forearm or behind your ear, and wait 24 to 72 hours for any reaction. This is especially important for exfoliating acids - they are active ingredients, and a patch test is the simplest way to understand how your skin will respond before it matters.

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

As a general rule, apply water-based serums from thinnest to thickest. Hyaluronic acid goes on first, on damp skin. Exfoliating acids follow. Moisturiser seals everything in.

Do not layer multiple exfoliating acids in the same routine. If you want to use both a glycolic acid toner and a BHA serum, alternate them on different nights rather than using both simultaneously. The same logic applies to retinol and vitamin C - do not use exfoliating acids in the same routine as either of these; alternate them instead. For detailed guidance on what not to combine with retinol, see our guide on what not to mix with retinol.

Azelaic acid and tranexamic acid are generally compatible with most other actives - but always patch test when introducing any new combination.

Step 5 - Wear SPF Every Morning, Without Fail

Exfoliating acids - particularly AHAs - increase the skin’s photosensitivity. By removing the outermost layer of dead skin cells, they reduce the skin’s minimal natural buffer against UV exposure. This does not mean you cannot use acids; it means daily SPF is not optional when you do.

Use exfoliating acids in your PM routine only - cleanse, apply your acid step, and follow with moisturiser. The next morning, apply a broad-spectrum SPF before anything else. Our Dewy Sunscreen SPF 30 offers reliable daily protection without the heavy, white-cast texture that puts people off wearing SPF consistently.

PHAs, azelaic acid, tranexamic acid, and hyaluronic acid do not increase photosensitivity - but daily SPF remains a skin health fundamental regardless of which acids you use.

For step-by-step guidance on building a complete routine around your acid of choice, visit our Complete Skincare Routine Guide.

You now know how to start - but which acid should you start with? Here is a straightforward guide to matching each acid to your specific skin concern.

Which Acid Is Right for Your Skin Concern?

You do not need every acid in this guide. You need the right one - or at most, two - matched to your actual skin concerns. Here is a direct, scannable reference to help you decide.

Dull Skin or Uneven Texture

Glycolic acid is your starting point. Its small molecule size and deep surface penetration make it the most effective AHA for resurfacing dull, rough, or uneven skin. Our Glycolic Acid Toner (£13) is a proven first step, used two to three times per week in your PM routine.

Oily Skin, Congested Pores or Blackheads

This is the BHA category. Salicylic acid - oil-soluble and pore-penetrating - is the only acid that can reach inside the pore to dissolve the debris causing congestion and blackheads. Start with our Salicylic Acid Cleanser (£12) for a daily active cleanse, or upgrade to our Beta Hydroxy Acid (BHA) Serum (£10) for leave-on action.

Blemishes and Breakouts

Salicylic acid remains the core recommendation - our Beta Hydroxy Acid (BHA) Serum (£10) provides targeted, overnight action. For a comprehensive blemish-clearing formula, our 360 Skin Clearing Serum is also worth considering as part of a complete blemish routine.

Sensitive Skin or First-Time Acid Use

Two options, depending on your goals. Our PHA Toner (£13) delivers gentle surface exfoliation with added hydration - ideal for sensitive or dry skin types who are new to acids. Our Mandelic Acid Treatment suits those who want gentle AHA exfoliation with some brightening action and antibacterial benefit, without the intensity of glycolic acid.

Dehydration or Dryness

Hyaluronic acid, without question. This is not an exfoliating acid - it is a humectant that locks water into the skin. Our Hyaluronic Acid Serum (£16 for 60ml) is suitable for all skin types and can be used daily, morning and night, on damp skin.

Visible Redness or Redness-Prone Skin

Azelaic acid is the most effective choice for calming persistent redness and reactive skin. Our 10% Azelaic Acid Serum(£16) works progressively to reduce visible redness and calm the skin’s inflammatory response - suitable for sensitive skin and rosacea-prone skin alike.

Dark Spots, Hyperpigmentation or Uneven Tone

Tranexamic acid is the targeted brightening choice. Our Tranexamic Acid Serum (£16) interrupts the melanin production process that causes dark spots and uneven pigmentation - and can be alternated with glycolic acid for those dealing with both pigmentation and texture concerns.

Rough Body Skin, Keratosis Pilaris or Ingrown Hairs

This is a glycolic acid job - but for the body. Our Glycolic Acid Exfoliating Body Stick (£15) is clinically proven to address KP bumps, ingrown hairs, and rough skin in as little as seven days, applied directly to dry skin on the arms, legs, or back.

Early Signs of Ageing or Fine Lines

Exfoliating AHAs - glycolic acid in particular - support cell turnover and progressively improve the appearance of fine lines with consistent use. Pair your glycolic acid step with a dedicated anti-ageing ingredient such as retinol (used PM, on alternate nights to your acids) for a comprehensive approach to visible ageing.

Remember: you do not need to address every concern at once. Start with the acid that matches your most pressing skin concern. For a complete breakdown of skin concerns and the ingredients that address them, see our Complete Skincare Concerns Guide.

Your Acids Questions, Answered

What is the best acid for beginners in skincare?

Mandelic acid or PHA are the best starting points for beginners. Both exfoliate gently with a low risk of irritation. PHAs are ideal for sensitive or dry skin types; mandelic acid suits those who want gentle exfoliation with some brightening action. Introduce either one or two times per week and build from there based on how your skin responds.

Can I use AHA and BHA together?

It is best to alternate rather than layer them in the same routine. Using both together significantly increases the risk of over-exfoliation and barrier disruption. Use an AHA toner on some nights and a BHA serum on others - your skin will still benefit from both acids without the risk of cumulative irritation.

What does glycolic acid do for skin?

Glycolic acid exfoliates the skin’s surface by dissolving the bonds between dead skin cells, accelerating cell turnover. The result is visibly smoother texture, a brighter and more even tone, refined pores, and - with consistent long-term use - a reduction in the appearance of fine lines. It is the most potent AHA and works best for normal to oily skin types.

What does salicylic acid do for skin?

Salicylic acid is a BHA that penetrates into the pore lining and dissolves excess oil and dead skin cells from within. It unclogs pores, reduces the visibility of blackheads, and helps prevent blemishes and breakouts from forming. It is the most effective acid for oily and congested skin.

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

AHAs are water-soluble acids that exfoliate the skin’s surface - best for dullness, texture, and uneven tone. BHAs are oil-soluble and penetrate into pores - best for oiliness, congestion, and breakouts. PHAs are the largest-molecule exfoliating acids, providing gentler surface exfoliation with added hydration - best for sensitive skin. All three exfoliate, but they work at different depths and suit different skin types.

When should I use acids in my skincare routine?

Most exfoliating acids - AHAs and BHAs - should be used in your PM routine only, as they increase photosensitivity. Apply after cleansing, before serums and moisturiser. PHAs can sometimes be used in the AM when followed by SPF. Hydrating acids like hyaluronic acid and specialty acids like azelaic and tranexamic acid can be used in both AM and PM routines.

Can I use hyaluronic acid and glycolic acid together?

Yes - hyaluronic acid and glycolic acid work well together. Apply hyaluronic acid first to damp skin, then follow with glycolic acid. The hyaluronic acid helps maintain hydration levels, which can offset any dryness that glycolic acid may cause over time.

What is azelaic acid good for?

Azelaic acid is best for reducing visible redness, fading post-blemish marks, and evening out skin tone. It has antibacterial properties and is one of the most well-tolerated actives in skincare - suitable for sensitive, rosacea-prone, and darker skin tones. It can be used morning and evening and does not increase photosensitivity.

Do I need SPF when using acids?

Yes. Exfoliating acids - particularly AHAs - increase the skin’s sensitivity to UV exposure by removing the surface layer of dead skin cells. Daily SPF is essential. Use exfoliating acids in your PM routine and apply broad-spectrum SPF every morning without exception.

The Bottom Line on Skincare Acids

There is an acid for every skin concern. That is not a marketing line - it is the practical reality of what this category of ingredients offers. Whether your goal is brighter skin, clearer pores, less redness, fewer dark spots, or better hydration, there is a specific acid - backed by clinical evidence - that addresses it directly.

The challenge has never been a lack of effective options. It has been a lack of clear information. Once you understand how each acid works, who it is for, and how to use it safely, the decision becomes straightforward. One well-chosen acid, used consistently and correctly, is all you need to start seeing results. You do not need a ten-step acid routine. You need the right one.

INKEY exists to give people that information without the noise - and if you are still unsure where to begin, the askINKEY team is available to help you work it out.

Build a routine around your acid of choice using our Complete Skincare Routine Guide, or explore all of INKEY’s acid products in Shop Skincare.

Not sure which acid is right for your skin? Take our Skincare Quiz and get a personalised routine in just 2 minutes.

Explore all skin concerns and the right ingredients for each in our Complete Skincare Concerns Guide.