Skincare acids are one of the most effective and widely-used categories of active ingredients available - and yet, for most people, they remain one of the most misunderstood. You have probably seen glycolic acid toners, salicylic acid cleansers, and hyaluronic acid serums sitting side by side on the same shelf, each claiming to transform your skin. But what does each one actually do? Which one is right for you? And how do you use them without damaging your skin barrier?

The word “acid” can sound alarming. It conjures images of lab coats and cautionary labels. But in skincare, acids work at low concentrations that have been refined and tested across decades of clinical research. Used correctly, they are some of the most powerful tools you can put to work for your skin.

This guide covers everything: every major acid family - AHAs, BHAs, PHAs, hydrating acids, and specialty acids - what each one does at a biological level, which skin types and concerns they suit, and how to introduce them into your routine safely. Whether you are completely new to acids or looking to build a more strategic routine, this is your master reference.

Our acid range spans from the Glycolic Acid Toner ($15) to the PHA Toner ($15) and 10% Azelaic Acid Serum($19.50) - each formulated around a specific skin concern, at a price that does not require a second mortgage. 

For building a full routine around your acid of choice, visit our Skincare Routine Guide and 10 Most Common Skin Concerns. Here is everything you need to know, broken down by acid type.

What Skincare Acids Are and How They Actually Work

Before diving into individual acid families, it is worth understanding what all skincare acids have in common - and where they differ. Establishing this foundation makes every subsequent section click into place.

An acid, in chemical terms, is a substance that donates hydrogen ions when dissolved in water, lowering the pH of a solution. In skincare, this lowered pH is precisely what gives acids their power. When applied to the skin’s surface, acids reduce the local pH, which loosens the bonds that hold dead skin cells together - a process known as desquamation. The result is that dead cells shed more efficiently, revealing fresher, brighter skin underneath.

This is the fundamental mechanism behind chemical exfoliation, and it is worth contrasting with physical exfoliation to understand why it is generally the preferred approach. Physical exfoliants - scrubs, face brushes, muslin cloths - work by manually abrading the skin’s surface. The problem is that this abrasion is difficult to control. Too much pressure, too rough a texture, and you risk creating micro-tears in the skin - tiny invisible wounds that can lead to inflammation, sensitivity, and long-term barrier damage. Chemical exfoliation, by contrast, is far more precise. The acid does the work at a molecular level, and the concentration of the formula determines how powerful that action is.

This brings us to a critical point: concentration and pH both matter enormously. A higher concentration of an acid, combined with a lower pH, produces a stronger exfoliating action. This is why a professional chemical peel performed in a clinic - with concentrations sometimes exceeding 30% and a pH close to 1 - produces far more dramatic results than an at-home toner formulated at 10% with a pH closer to 3.5. Over-the-counter products are calibrated specifically for safe home use, which is why, when used as directed, they deliver results without the recovery period associated with clinical peels.

One more thing to establish clearly: not all skincare acids exfoliate. This is one of the most common misconceptions. Hyaluronic acid does not exfoliate - it hydrates. Tranexamic acid does not resurface the skin - it targets pigmentation. Azelaic acid does not primarily function as a peeling agent - it reduces redness and inhibits melanin production. Understanding the purpose of each acid type is the difference between a routine that delivers real results and one that creates confusion and frustration.

Molecular size also plays a defining role. Different acids have different molecular weights, which determines how deeply they penetrate into the skin. Smaller molecules travel further; larger molecules stay closer to the surface. This is why glycolic acid - the smallest AHA - is the most potent of its family, and why PHAs, with their comparatively large molecules, exfoliate gently enough for even reactive skin.

The FDA notes that alpha hydroxy acids have been extensively studied for their exfoliating properties and that, at concentrations approved for cosmetic use, they have a strong safety profile when used with appropriate sun protection. The science behind skincare acids is not new or experimental. It is well-established.

pH is also a relevant consideration when you start layering multiple active ingredients - for guidance on which ingredients work well alongside acids and which do not, see our guide on what skincare ingredients you should not layer together.

Used correctly, skincare acids are safe, effective, and genuinely transformative across all skin types. 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 - Glycolic, Lactic, and Mandelic Acid Explained

Alpha Hydroxy Acids, or AHAs, are the most familiar acid family in skincare - and for good reason. They have decades of clinical backing, a well-understood mechanism of action, and a proven track record across a wide range of skin concerns. According to a topical AHA clinical review published in the journal Cosmetics, AHAs stimulate skin cell renewal and demonstrably improve surface texture, tone, and the appearance of fine lines with regular use.

AHAs are water-soluble, which is the first thing to understand about how they work. Being water-soluble means they function at the skin’s surface - they dissolve the bonds between dead skin cells in the outermost layer, encouraging those cells to shed and accelerating the natural renewal process. They do not penetrate into pores, which means they are excellent for surface concerns like dullness, uneven texture, and tone - but less suited to congestion and oiliness than oil-soluble acids like BHAs.

Most AHAs are derived from natural sources. Glycolic acid comes from sugarcane. Lactic acid is derived from milk. Mandelic acid is extracted from bitter almonds. This natural origin is part of what makes the AHA family feel approachable, but it is the chemistry - not the source - that produces results.

The key benefits of AHAs as a family:

• Improved skin texture and smoothness
• Brighter, more even skin tone
• Reduced appearance of fine lines over time
• Fading of dark marks and post-blemish discoloration
• Increased cell turnover, which supports overall skin health

If texture is your primary concern, our guide on how to improve skin texture covers this in more detail. For a direct head-to-head comparison of AHAs and BHAs, see our AHA vs BHA breakdown.

Glycolic Acid - The Most Potent AHA

Glycolic acid has the smallest molecular size of all the AHAs. This seemingly minor detail has major implications. Because its molecule is so small, glycolic acid penetrates more deeply into the skin than any other member of its family - making it the most powerful AHA available in cosmetic formulations. If you want meaningful, visible results from an AHA, glycolic acid is where you start.

What does glycolic acid do? It accelerates cell turnover, dissolves dead skin cell bonds at the surface, improves skin texture, visibly brightens the complexion, reduces the appearance of enlarged pores, and over time, helps diminish fine lines and uneven pigmentation. It is a genuinely multi-tasking ingredient.

Glycolic acid is best suited to normal, combination, and oily skin types. Its potency makes it less suitable for sensitive skin - those with reactive complexions are better served by lactic or mandelic acid, or a PHA. If you are new to acids entirely, glycolic is not the place to start unless your skin is resilient.

Our Glycolic Acid Toner ($15) delivers 10% glycolic acid alongside 5% witch hazel, providing both exfoliation and pore-minimizing action in a single leave-on formula. Use it in the evening only, one to three times per week to begin with, applied after cleansing. No rinsing required. Always follow with a broad-spectrum SPF the next morning.

Glycolic acid also performs exceptionally well on the body. Our Glycolic Acid Exfoliating Body Stick ($19.50) is clinically proven to address keratosis pilaris (those stubborn rough bumps on the backs of arms and thighs), ingrown hairs, and rough skin texture - with visible results within seven days. It is one of the most effective body exfoliants available at any price point.

Lactic Acid - The Gentler Entry Point

Lactic acid shares glycolic acid’s mechanism but has a larger molecular size - meaning it penetrates less deeply and acts more gently on the skin. This makes it the natural starting point for anyone who wants to try an AHA but is cautious about sensitivity or reactivity.

Beyond exfoliation, lactic acid has a secondary property that sets it apart from glycolic: it is a humectant. This means it attracts water to the skin as it exfoliates, making it a particularly good choice for those with dry or dehydrated skin who want the brightening and smoothing benefits of an AHA without compromising their moisture levels.

Lactic acid is best for dry, normal, and mildly sensitive skin types. It targets dullness, mild texture irregularities, early fine lines, and dehydration-related flatness. For first-time acid users who are not confident about how their skin will respond, lactic acid is frequently the recommended starting point - a gentler introduction to the AHA family before progressing to glycolic acid.

Mandelic Acid - The Most Gentle AHA

Mandelic acid is the largest-molecule AHA, which makes it the slowest to penetrate the skin and the gentlest of the three. But its value goes beyond just being a mild exfoliant - mandelic acid has a unique dual action that makes it particularly interesting. It is both a surface exfoliant and antibacterial, which gives it relevance for acne-prone skin as well as for those simply seeking texture improvement.

Because mandelic acid penetrates slowly and sits predominantly at the skin’s surface, it carries a significantly lower risk of post-inflammatory hyperpigmentation than glycolic acid. This makes it one of the safest AHA choices for darker skin tones, where inflammation from stronger acids can trigger unwanted darkening of the skin.

Mandelic acid is best for sensitive skin, darker skin tones, and anyone approaching acids for the first time. Its benefits include gentle exfoliation, improved skin tone, reduced appearance of post-acne marks, and gradual brightening - without the intensity that puts many people off acid use entirely.

Our Mandelic Acid Treatment ($14) delivers targeted mandelic acid action for those who need effective but genuinely gentle exfoliation.

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

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

Beta Hydroxy Acids - BHAs - are fundamentally different from AHAs in one defining way: they are oil-soluble. Where AHAs are water-soluble and work on the skin’s surface, BHAs can cut through sebum (the skin’s natural oil) and penetrate directly into the pore lining. This makes them an entirely different category of exfoliant, suited to an entirely different set of concerns.

According to the FDA, beta hydroxy acids have been widely studied for their ability to penetrate oily skin and exfoliate within the pore - reducing congestion, preventing blockages, and improving the overall clarity of acne-prone complexions. For anyone dealing with oily skin, blackheads, enlarged pores, or frequent breakouts, a BHA is almost always the more effective choice over an AHA.

BHA vs AHA - the key differences at a glance:

• AHAs are water-soluble - they work on the skin’s surface, best for dullness, texture, and uneven tone.
• BHAs are oil-soluble - they penetrate into pores, best for oiliness, congestion, blackheads, and acne.
• If your concern is predominantly surface-level, choose an AHA. If it lives inside the pore, choose a BHA.
  

Salicylic Acid - The Gold Standard for Oily and Acne-Prone Skin

Salicylic acid is the most widely used BHA in skincare, and it has earned that position entirely on the strength of its results. Derived from willow bark, it works by penetrating the pore lining and dissolving the mixture of excess sebum and dead skin cells that accumulate inside and cause blockages. The result: clearer pores, fewer blackheads, reduced oiliness, and a measurable decrease in acne frequency over time.

What does salicylic acid do beyond unclogging pores? It also has mild anti-inflammatory properties, which means it can reduce the redness and swelling associated with active acne - not just prevent it from forming. It helps smooth skin texture, tighten the appearance of enlarged pores, and control the excess oil production that makes congestion an ongoing problem for many people.

Salicylic acid is best for oily, combination, and acne-prone skin. It is generally well-tolerated, but those with dry or sensitive skin should use it with care - starting once or twice a week and building frequency based on how their skin responds.

INKEY offers two salicylic acid formats, each serving a different step in your routine:

• Our Salicylic Acid Cleanser ($14) delivers 2% salicylic acid alongside 1% zinc for additional oil-control support. Use it as your first or second cleanse in your PM routine - or daily if your skin is resilient. It can also be used on the chest, back, and decolletage, making it genuinely versatile for body acne.
• Our Beta Hydroxy Acid (BHA) Serum ($11) is a leave-on serum that provides more targeted, sustained salicylic acid action. Because it stays on the skin rather than being rinsed away, it works for longer - making it the stronger of the two options for congestion and blackhead clearance.

Succinic Acid - A Gentler Option for Reactive Skin

Succinic acid is a dicarboxylic acid that functions similarly to BHAs in its action on acne-prone skin, though it takes a gentler approach. Derived from amber, it works primarily by calming the skin, reducing redness around blemishes, and helping to balance oil production. INKEY’s formulation also includes 1% salicylic acid - giving it dual-action effect, the calming properties of succinic alongside the pore-clarifying action of salicylic.

If you have found salicylic acid too strong, or if your skin is on the more sensitive end of the oily spectrum, succinic acid is worth considering. It is also a good option for those who experience occasional breakouts rather than persistent congestion - providing targeted support without the daily strength of a full BHA routine.

Our Succinic Acid Treatment ($16) is formulated as a targeted spot treatment, designed to be applied directly to areas of concern rather than across the whole face.

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 - The Gentle Exfoliant That Works for Sensitive Skin

Polyhydroxy Acids - PHAs - are the youngest of the three main exfoliating acid families, and in many ways the most misunderstood. They are often described simply as “a weaker AHA,” which fundamentally undersells what makes them clinically interesting and practically valuable. PHAs are not just a diluted version of glycolic acid - they are a distinct acid category with their own unique set of benefits.

The defining characteristic of PHAs is their molecular size. PHA molecules are significantly larger than those of AHAs or BHAs, which means they penetrate the skin slowly and remain predominantly at the surface. This results in effective exfoliation - clearing dead skin cells, improving texture, and gradually brightening the complexion - but with considerably less irritation potential than the deeper-penetrating acid families. For skin types that have historically reacted poorly to AHAs or BHAs, PHAs offer a genuinely viable alternative rather than an inferior substitute.

What truly sets PHAs apart is their dual function. Unlike most exfoliating acids, PHAs are also humectants - they attract and retain moisture. This means they exfoliate and hydrate simultaneously, a combination that is unusually well-suited to dry, compromised, or reactive skin. You get the benefits of chemical exfoliation without the dryness or tightness that some people experience with AHAs.

The primary PHA used in skincare is gluconolactone - the active ingredient in our PHA Toner.

PHAs are best suited to:

• Sensitive and reactive skin types
• Dry or dehydrated skin
• Anyone who has had a bad reaction to AHAs or BHAs in the past
• First-time acid users who want a gentle introduction
• Those with a compromised skin barrier
• Pregnant skin (PHAs are generally considered pregnancy-safe - though always check with your doctor or midwife)

The benefits of regular PHA use include:

• Gentle surface exfoliation without stripping
• Improved skin texture and smoothness
• A brighter, more even complexion over time
• A hydration boost that supports the skin barrier
• Minimal risk of post-inflammatory reactions

Our PHA Toner ($15) delivers 3% gluconolactone in a gentle, leave-on toner format. Because of its inherently lower irritation potential, it can be used more frequently than AHAs or BHAs - though, as with all acids, starting gradually and building frequency based on tolerance is always the right approach. Our Glycolic Acid Toner product page itself recommends the PHA Toner as the alternative for those with sensitive skin - a real, substantiated recommendation based on how the two products perform across different skin types.

For body use, our PHA Body Water Cream brings the same gentle exfoliating and hydrating properties of PHA to the body - ideal for sensitive skin that cannot tolerate stronger glycolic acid body formulas.

Comparing the three exfoliating acid families:

• AHAs (e.g. Glycolic, Lactic, Mandelic): Water-soluble. Surface exfoliation. Moderate-to-strong penetration depending on molecule size. Best for dull, dry, and sun-damaged skin. Sensitivity level: low to moderate.
• BHAs (e.g. Salicylic): Oil-soluble. Penetrates into the pore. Strong, targeted action. Best for oily, congested, and acne-prone skin. Sensitivity level: moderate.
• PHAs (e.g. Gluconolactone): Water-soluble. Slow, surface-level penetration. Gentle action with added hydration. Best for sensitive, dry, or reactive skin. Sensitivity level: low.

PHAs offer comparable surface exfoliation to gentle AHAs like lactic acid, but with significantly lower irritation potential - making them ideal for those who find AHAs too strong.

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. This is one of the most important distinctions to understand, because it shapes how you approach building a routine. Hyaluronic acid, azelaic acid, and tranexamic acid are each classified as acids by chemistry - but their functions in skincare are completely different from AHAs, BHAs, or PHAs. Understanding what each one does allows you to address multiple skin concerns simultaneously without the risk of over-exfoliation.

A quick reference for the specialty acids:

Hydrate it: Hyaluronic Acid

Calm it: Azelaic Acid

Brighten it: Tranexamic Acid

Hyaluronic Acid - The Skin’s Master Hydrator

Let’s be completely clear from the start: hyaluronic acid does not exfoliate. It is not an active exfoliant in any sense. It is a humectant - a substance that attracts and binds water molecules - and it is one of the most effective hydrating ingredients available in skincare.

Hyaluronic acid is a naturally occurring polysaccharide found in the skin, connective tissue, and eyes. In its natural state in the body, it holds up to 1,000 times its own weight in water. In skincare, it functions by drawing moisture from the environment and from deeper layers of the skin to the surface, providing immediate and sustained hydration. The result is plumper, more supple skin, a visible reduction in fine lines caused by dehydration, and improved overall skin texture and feel.

One of the more sophisticated aspects of hyaluronic acid formulations is the role of molecular weight. Not all hyaluronic acid molecules are the same size - and different molecular weights reach different depths in the skin. High molecular weight hyaluronic acid sits on the surface and provides immediate plumping. Low molecular weight versions penetrate more deeply and provide lasting hydration within the skin’s layers. Multi-weight formulations deliver hydration across multiple levels simultaneously.

Hyaluronic acid suits every skin type - oily, dry, combination, sensitive, and everything in between. It is one of the few truly universal skincare ingredients. And critically, it is compatible with exfoliating acids - it can be used in the same routine, applied to damp skin before your exfoliating acid step to support hydration throughout.

Our Hyaluronic Acid Serum ($10) delivers 2% pure hyaluronic acid at three molecular weights, alongside Matrixyl 3000 - a peptide complex that supports collagen production. Apply to damp skin for maximum absorption and deepest penetration. It can be used morning and evening.

Azelaic Acid - The Redness and Tone-Evening Acid

Azelaic acid is one of the most underrated ingredients in skincare. It does not exfoliate in the conventional sense, and it does not hydrate like hyaluronic acid. What it does is more specific and, for the right person, transformative: it reduces visible redness, fades post-acne marks, and helps even out skin tone through a mechanism that most other skincare acids cannot replicate.

Azelaic acid works by inhibiting the production of melanin - the pigment responsible for dark marks and uneven tone - and by calming inflammatory responses in the skin. It has antibacterial properties that make it relevant for acne-prone skin, and it has been studied extensively for its efficacy in reducing the visible signs of rosacea. What makes azelaic acid particularly notable is not just what it does, but how it does it: gently, with a high tolerance profile that makes it one of the safest actives available.

Azelaic acid is suitable for sensitive skin, redness-prone and rosacea-prone skin, and is one of the few actives considered safe during pregnancy (though always check with your doctor or midwife). It is also considered safe for darker skin tones - it does not carry the risk of worsening hyperpigmentation that some stronger exfoliating acids present.

For incorporating azelaic acid into your routine: apply after cleansing, before your moisturizer. It can be used in the morning or evening - or both, if your skin tolerates it well. It pairs well with hyaluronic acid and is generally compatible with most other skincare ingredients.

Our 10% Azelaic Acid Serum ($19.50) delivers a clinically effective concentration in a lightweight serum format, targeting redness, post-acne marks, and uneven skin tone with consistent use.

For more on improving skin texture alongside brightening, see our guide on how to improve skin texture.

Tranexamic Acid - The Targeted Brightening Acid

Tranexamic acid is perhaps the least immediately recognizable name in this guide - but it is increasingly being regarded by skin experts as one of the most effective brightening ingredients available in cosmetic skincare, particularly for stubborn pigmentation.

Tranexamic acid is a synthetic amino acid derivative that works by interrupting the biochemical signaling pathway between keratinocytes (skin cells) and melanocytes (pigment-producing cells). In simpler terms: it blocks the messages that tell the skin to produce excess melanin, which is what causes dark spots, hyperpigmentation, and uneven tone. It does not exfoliate the skin, and it does not increase photosensitivity - it works at a cellular communication level.

This mechanism makes tranexamic acid particularly effective on stubborn pigmentation that other brightening approaches have failed to shift - including melasma, post-inflammatory hyperpigmentation, and sun-induced dark spots. It is also notably well-tolerated by sensitive and darker skin tones, where some other brightening agents can cause irritation.

Tranexamic acid is best for uneven skin tone, hyperpigmentation, dark spots, and dull complexions. It works well alongside exfoliating AHAs - using them on alternating nights can compound brightening results over time.

Our Tranexamic Acid Serum ($18) is formulated to be used morning or evening, either alone or as part of a broader brightening 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 Introduce Acids Into Your Skincare Routine Safely

Knowing which acid is right for your skin concern is only half the equation. The other half is knowing how to use it without overwhelming your skin. Done correctly, introducing acids is straightforward. Done incorrectly, it can lead to sensitivity, irritation, and the kind of bad experience that puts people off active ingredients entirely. Here is how to get it right.

Step 1 - Start With One Acid Only

The most common mistake people make when starting with acids is introducing multiple products at once. It is tempting when you are excited about results, but it is counterproductive. If your skin reacts, you will not know which product caused the problem. If your skin adapts well, you will not know which ingredient is delivering the benefit.

Choose the single acid that best matches your primary skin concern - using the guide in the next section to help you - and commit to it alone for a minimum of four to six weeks before considering adding anything else. Patience here is not a limitation. It is strategy.

Step 2 - Start Slowly With Frequency

More is not better with exfoliating acids. Starting too frequently is one of the most reliable ways to disrupt your skin barrier and end up red, tight, and flaky - none of which is the goal.

For AHAs and BHAs, begin with once or twice per week. Stick at that frequency for two to four weeks, then increase to three times per week if your skin is responding well. PHAs can be introduced more frequently than AHAs or BHAs, given their inherently lower irritation potential - but the same logic applies: start slowly and build. Hydrating acids like hyaluronic acid and specialty acids like azelaic acid and tranexamic acid do not exfoliate, so they can generally be used daily from the outset without the same risk.

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 sign of reaction - redness, itching, swelling, or unusual sensitivity. This step takes less than a minute and can save you significant discomfort.

Patch testing is especially important with exfoliating acids - AHAs and BHAs - which are active ingredients capable of causing irritation when your skin is not prepared for them. Learn exactly how to patch test and why it matters in our guide: why do I need to do a patch test?

Step 4 - Get Your Routine Order Right

Layering acids correctly within your routine matters. A few key rules to follow:

1. Apply hyaluronic acid first, on damp skin, before any exfoliating acid steps. This provides a hydration base and helps offset any potential dryness from AHAs or BHAs.
2. Apply exfoliating acids (AHA toners, BHA serums) after cleansing and any hydrating layers.
3. Do not use multiple exfoliating acids in the same routine - for example, do not apply a glycolic acid toner and a BHA serum on the same evening. Alternate them on different nights instead.
4. Avoid using exfoliating acids in the same routine as retinol or vitamin C. These are powerful actives that need space to perform without competing for absorption or compounding irritation risk. For detailed guidance on what not to layer with retinol specifically, see our guide on what not to mix with retinol.
5. Azelaic acid and tranexamic acid are generally more forgiving when it comes to layering - they are compatible with most other actives - but always patch test when combining anything new.

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

Step 5 - SPF Is Non-Negotiable

Exfoliating acids - particularly AHAs - increase the skin’s sensitivity to UV radiation. This happens because they remove the outermost layer of dead skin cells, which provides a small but meaningful natural barrier against sun exposure. Remove that layer and your skin is more vulnerable to UV damage, including the very hyperpigmentation that many people use acids to address in the first place.

This does not mean you cannot use acids. It means daily SPF is non-negotiable when you do. Use exfoliating acids in your PM routine, and apply a broad-spectrum SPF every morning without exception. PHAs, azelaic acid, tranexamic acid, and hyaluronic acid do not increase photosensitivity - but daily SPF is always recommended as a fundamental of skin health, regardless of your routine.

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

Which Acid Is Right for Your Skin Concern?

This is the practical section - the one to come back to, save, and share. Each entry below matches a common skin concern to the right acid, with a brief explanation of why it works and a direct link to the INKEY product that delivers it. You do not need every acid. Start with the one that addresses your biggest concern, and go from there.

Dull Skin and Uneven Texture

The acid: Glycolic Acid
Why: Glycolic acid’s small molecule size makes it the most effective surface exfoliant in the AHA family. It accelerates cell turnover, removes the build-up of dead cells that cause dullness, and reveals noticeably brighter, smoother skin with consistent use.
Start here: Our Glycolic Acid Toner ($15). Use 1-3x per week, PM only.

Oily Skin, Congested Pores, and Blackheads

The acid: Salicylic Acid
Why: Oil-soluble BHAs are the only exfoliating acid family that can penetrate inside the pore and dissolve the sebum-and-dead-cell build-up at the root of congestion and blackheads. No surface acid can match them for this concern.
Start here: Our Salicylic Acid Cleanser ($14) for a daily active cleanse, and/or our Beta Hydroxy Acid (BHA) Serum($11) for more targeted leave-on action.

Acne and Breakouts

The acid: Salicylic Acid (with optional succinic acid for gentler targeted treatment)
Why: Salicylic acid unclogs the pores where acne forms, reduces the bacterial environment that allows it to develop, and has mild anti-inflammatory action to calm redness around existing breakouts.
Start here: Our Beta Hydroxy Acid (BHA) Serum ($11). For a more targeted approach on individual breakouts, consider our Succinic Acid Treatment ($16). For a comprehensive acne routine, explore our 360 Acne Skin Clearing Serum.

Sensitive Skin and First-Time Acid Use

The acid: PHA (Gluconolactone) or Mandelic Acid
Why: PHAs deliver effective exfoliation at the skin’s surface without the deeper penetration - or the irritation risk - of AHAs or BHAs. Mandelic acid offers gentle exfoliation with additional antibacterial benefits, at a lower irritation risk than glycolic acid.
Start here: Our PHA Toner ($15), 1-3x per week to begin. For those who want an AHA with very low irritation risk, our Mandelic Acid Treatment ($14) is the gentlest option in that family.

Dehydration and Dryness

The acid: Hyaluronic Acid
Why: Hyaluronic acid does not exfoliate - it hydrates. If dryness and dehydration are your primary concern rather than texture or congestion, this is your starting point. It can also be used alongside any exfoliating acid to support moisture levels.
Start here: Our Hyaluronic Acid Serum ($10). Apply to damp skin, morning and evening.

Redness and Redness-Prone Skin

The acid: Azelaic Acid
Why: Azelaic acid reduces visible redness through its anti-inflammatory mechanism, unlike exfoliating acids which can temporarily increase skin sensitivity. It is one of the most well-tolerated actives for reactive skin types.
Start here: Our 10% Azelaic Acid Serum ($19.50). Use AM or PM, before moisturizer.

Dark Spots, Hyperpigmentation, and Uneven Tone

The acid: Tranexamic Acid (optionally combined with Glycolic Acid on alternating nights)
Why: Tranexamic acid addresses pigmentation at a cellular signaling level - blocking the process that causes excess melanin production. Paired with a surface exfoliant like glycolic acid on alternating nights, it provides a comprehensive approach to uneven tone.
Start here: Our Tranexamic Acid Serum ($18). Use AM or PM. Alternate with our Glycolic Acid Toner ($15) on opposite evenings for compounded brightening.

Rough Body Skin, Keratosis Pilaris, and Ingrown Hairs

The acid: Glycolic Acid (body)
Why: Glycolic acid’s small molecule size and potent exfoliating action make it highly effective on the thicker skin of the body, where surface cell build-up causes the rough, bumpy texture characteristic of keratosis pilaris and ingrown hairs.
Start here: Our Glycolic Acid Exfoliating Body Stick ($19.50). Clinically proven to deliver visible improvement within seven days.

Early Signs of Aging and Fine Lines

The acid: Glycolic Acid (for exfoliation) paired with a dedicated anti-aging step
Why: AHAs, particularly glycolic acid, support cell turnover and can reduce the appearance of fine lines over time by revealing fresher skin at the surface. For a more targeted anti-aging approach, pair glycolic acid in your PM routine with a retinol product on alternating nights - not the same night.
Start here: Our Glycolic Acid Toner ($15) on some evenings; introduce a retinol on alternate evenings.

A final reminder: you do not need every acid in this list. Skin concerns are often interconnected, and a single well-chosen acid, used consistently, will deliver more results than five mediocre ones used inconsistently. Start with your biggest concern, be patient, and build from there. For a deeper exploration of common skin concerns and the right ingredients for each, visit our 10 Most Common Skin Concerns guide.

Frequently Asked Questions About Skincare Acids

What is the best acid for beginners in skincare?

Mandelic acid or PHA are the best starting points for first-time acid users. Both exfoliate gently with a low risk of irritation. PHAs are particularly ideal for sensitive or dry skin, while mandelic acid suits those who want gentle exfoliation alongside some brightening action. Start with once or twice per week and build from there as your skin adapts.

Can I use AHA and BHA together?

It is best to alternate AHAs and BHAs rather than layer them in the same routine. Using both together significantly increases the risk of over-exfoliation and barrier disruption, which can result in sensitivity, redness, and peeling. Use an AHA on some evenings and a BHA on others - your skin will still benefit from both without the risk of 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 and revealing brighter, smoother skin underneath. With consistent use, it reduces the appearance of uneven texture, enlarged pores, fine lines, and dull tone. It is the most potent AHA available in cosmetic skincare, 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 into the pore lining and dissolves the excess sebum and dead skin cells that cause blockages. It unclogs pores, reduces the appearance of blackheads, helps prevent acne and breakouts from forming, and controls excess oil production over time. It is the most effective acid choice for oily and acne-prone skin.

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

AHAs are water-soluble acids that exfoliate the skin’s surface - best for dullness, uneven texture, and uneven tone. BHAs are oil-soluble and penetrate into pores - best for oiliness, congestion, blackheads, and acne. PHAs are the largest-molecule exfoliating acids, providing gentler surface exfoliation with the added benefit of hydration - best for sensitive, dry, or reactive skin. All three exfoliate, but they do so 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 the skin’s photosensitivity. Apply after cleansing, before serums and moisturizer. PHAs can sometimes be used in the AM with SPF due to their gentler nature. Hydrating acids like hyaluronic acid and specialty acids like azelaic acid and tranexamic acid can be used AM or PM without photosensitivity concerns.

Can I use hyaluronic acid and glycolic acid together?

Yes - hyaluronic acid and glycolic acid are compatible and work well together in the same routine. Apply hyaluronic acid first to damp skin, then follow with your glycolic acid step. The hyaluronic acid helps maintain skin hydration, which can offset the dryness that some people experience when using glycolic acid - making the combination more comfortable and effective than using glycolic acid alone.

What is azelaic acid good for?

Azelaic acid is best for reducing visible redness, fading the appearance of post-acne marks, and evening out skin tone. It has antibacterial properties that make it useful for acne-prone skin and anti-inflammatory properties that make it valuable for redness-prone and rosacea-prone complexions. It is one of the most well-tolerated actives in skincare, suitable for sensitive and darker skin tones, and is generally considered safe during pregnancy.

Do I need to use SPF when using acids?

Yes - daily SPF is essential when using exfoliating acids, particularly AHAs. These acids remove the surface layer of dead skin cells, which increases the skin’s vulnerability to UV radiation. Use exfoliating acids in your PM routine and apply a broad-spectrum SPF every morning without exception. PHAs, azelaic acid, tranexamic acid, and hyaluronic acid do not increase photosensitivity - but daily SPF is always recommended as a skin health fundamental regardless of your routine.

The Right Acid, Used Well, Will Change Your Skin

There is an acid for every skin concern. The key - and it really is this simple - is knowing which one is right for you and how to introduce it into your routine in a way that lets it do its job without overwhelming your skin. That is what this guide has set out to give you.

Acids are not complicated. They have been made to feel complicated by an industry that sometimes prioritizes mystique over clarity. At INKEY, the approach has always been the opposite: give people the information they need, strip away the noise, and let the ingredients speak for themselves. The science behind AHAs, BHAs, PHAs, and specialty acids is robust, well-understood, and genuinely accessible - and now, so is your understanding of it.

You do not need a cabinet full of acids to see results. You need one well-chosen acid, used consistently, at the right frequency, with SPF in the morning. That single decision, made correctly, has the power to meaningfully improve your skin over time.

If you are still unsure where to begin, INKEY’s askINKEY team is available 24/7 on live chat - staffed by real people who know their ingredients and are there to help you find the right starting point for your skin.

Build a routine around your acid of choice using our Skincare Routine Guide, or browse 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 personalized routine recommendation in two minutes.

Explore the most common skin concerns and how to address them in our 10 Most Common Skin Concerns guide.