Acids in Skincare Explained: Comparing AHAs, BHAs, PHAs and Other Cosmetic Acids

Let’s stir up some magic in the lab with today’s hot topic: acids in skincare, what makes them different, how they work and which ones deserve a place in your next cosmetic formulation!

Glycolic Acid, Lactic Acid, Salicylic Acid, Azelaic Acid, Kojic Acid… The skincare industry certainly loves its acids!

But if you’re just beginning your cosmetic formulation journey, choosing between them can feel like standing in front of an enormous dessert menu where everything sounds delicious, but you have absolutely no idea what to order.

Should you choose Glycolic Acid for exfoliation? Is Mandelic Acid better for sensitive skin? What’s the difference between AHAs, BHAs and PHAs? And why do some acids help with pigmentation while others are mainly antioxidants?

Well, grab your coffee because we’re about to make sense of this fascinating ingredient family!

Understanding the differences between cosmetic acids will help you develop more effective skincare products, avoid formulation mistakes and select ingredients based on chemistry rather than marketing trends.

What Are Acids in Cosmetic Formulation?

First, let’s clear up a common misconception. Not every ingredient containing the word acid is an exfoliating ingredient.

In cosmetic chemistry, acids represent a broad family of substances with very different properties and functions.

Some acids encourage the removal of dead skin cells, others help improve uneven skin tone, while certain acids provide antioxidant benefits or help adjust a formulation’s pH.

For example, Glycolic Acid is primarily associated with exfoliation, while Ferulic Acid is valued for its antioxidant properties. And Hyaluronic Acid? Despite its name, it’s primarily used for hydration rather than exfoliation.

See why understanding ingredient chemistry is so important?

Let’s start with the three major categories of exfoliating acids.

AHAs: Alpha Hydroxy Acids for Exfoliation and Skin Renewal

Alpha Hydroxy Acids, commonly called AHAs, are water-soluble acids frequently used in exfoliating skincare formulations.

They help promote the shedding of dead skin cells, improving the appearance of uneven texture, dullness and certain superficial pigmentation concerns.

However, different AHAs have different characteristics.

Glycolic Acid: The Powerful Exfoliator

Glycolic Acid is one of the best-known exfoliating acids in skincare. Its relatively small molecular size contributes to its ability to penetrate the skin, making it particularly interesting for formulations targeting uneven texture and visible signs of photoageing.

However, Glycolic Acid can also cause irritation, especially at higher concentrations or lower pH values. It’s therefore important to balance exfoliating performance with skin tolerance.

For beginner formulators, remember that Glycolic Acid concentration alone doesn’t determine exfoliating strength. The finished formulation’s pH and free-acid availability also matter.

Lactic Acid: Exfoliation Meets Hydration

If Glycolic Acid is the enthusiastic overachiever, Lactic Acid is its slightly more considerate cousin!

Lactic Acid also provides exfoliating benefits, but it has an additional advantage: it contributes to skin hydration. It’s naturally associated with the skin’s moisturising system and can help improve the appearance of dry, rough skin.

Research comparing Glycolic Acid and Lactic Acid has demonstrated that both can improve skin characteristics, although irritation potential depends on their concentration, chemical form and formulation.

Lactic Acid can therefore be an interesting option when developing exfoliating products that also emphasise moisturisation.

And it can also be used to adjust your formulation’s pH 😀

Mandelic Acid: An Interesting Option for Gentle Exfoliation

Mandelic Acid has a larger molecular structure than Glycolic Acid and is frequently positioned as a gentler exfoliating alternative. It’s particularly interesting for formulations targeting uneven skin tone, blemish-prone skin and consumers seeking milder exfoliation.

However, larger molecular size doesn’t automatically guarantee that an ingredient will be non-irritating. Formulation concentration, pH and overall product composition still matter.

From a practical perspective, Mandelic Acid also presents solubility considerations. Depending on the desired concentration, formulators may need suitable solvents or alternative processing strategies.

BHAs: Beta Hydroxy Acids for Blemish-Prone Skin

Now, let’s meet one of skincare’s most popular ingredients.

Salicylic Acid: The Blemish-Prone Skin Favourite

Salicylic Acid is commonly classified as a BHA in cosmetic skincare, although its chemical structure differs from a conventional beta-hydroxy carboxylic acid.

Unlike typical water-soluble AHAs, Salicylic Acid has limited water solubility and is particularly useful in formulations targeting oily and blemish-prone skin. Its exfoliating properties can help improve the appearance of clogged pores and uneven skin texture.

However, Salicylic Acid requires careful formulation. Its solubility, final pH and concentration must all be considered. Suitable solvents or solubilisation systems may be necessary to prevent crystallisation.

And here’s an important regulatory reminder! Salicylic Acid is restricted under European cosmetic legislation, with permitted concentrations depending on product type, intended function and other conditions.

PHAs: Polyhydroxy Acids for Gentle Exfoliation

If you’re developing skincare for consumers who find traditional exfoliating acids too aggressive, Polyhydroxy Acids deserve your attention.

PHAs generally have larger molecular structures and multiple hydroxyl groups, contributing to their water-binding properties. They’re frequently associated with gentler exfoliation and moisturising benefits.

Gluconolactone: Exfoliation and Moisturisation

Gluconolactone is one of the best-known PHAs used in skincare. It can contribute to gentle exfoliation while offering humectant properties. It’s particularly interesting for formulations targeting dry or sensitive-feeling skin.

Gluconolactone is also readily soluble in water, making it relatively convenient to incorporate into many aqueous formulations. However, its behaviour depends on pH and its conversion to Gluconic Acid in water.

Lactobionic Acid and Maltobionic Acid

Lactobionic Acid and Maltobionic Acid belong to the family of bionic acids, often discussed alongside PHAs. Both are valued for their moisturising properties and potential antioxidant benefits.

Lactobionic Acid is particularly interesting in formulations designed to support skin hydration and improve the appearance of roughness.

Maltobionic Acid offers similar formulation possibilities, although the available clinical evidence is less extensive than for some better-known exfoliating acids.

PHAs can be excellent formulation options, but gentle doesn’t mean irritation-free. As always, the complete formulation determines the finished product’s performance.

Azelaic Acid and Its Derivatives: More Than Exfoliation

Now we’re moving beyond traditional exfoliating acids!

Azelaic Acid

Azelaic Acid is a dicarboxylic acid widely recognised for its applications in products targeting blemishes and uneven skin tone. It’s also used in dermatological treatments for certain skin conditions.

In cosmetic formulation, one of its main challenges is its limited water solubility. This means formulators must carefully consider whether to use a suspension, an appropriate solvent system or another delivery approach.

Potassium Azeloyl Diglycinate

Potassium Azeloyl Diglycinate is an azelaic acid derivative with different physicochemical properties. Unlike Azelaic Acid, it’s water-soluble and is commonly used in formulations targeting uneven skin tone, sebum balance and hydration.

However, it shouldn’t be treated as a direct replacement for Azelaic Acid. The two ingredients have different chemical structures, formulation requirements and supporting evidence.

Always consult your supplier’s technical documentation before selecting concentrations or establishing your formulation’s pH.

Ferulic Acid: The Antioxidant Specialist

Not all acids are designed to exfoliate!

Ferulic Acid is a phenolic compound valued primarily for its antioxidant properties. It’s particularly interesting in formulations designed to help protect against oxidative stress. Ferulic Acid is frequently associated with antioxidant combinations containing Vitamins C and E.

However, its limited water solubility can make formulation challenging. Solvent selection, pH, ingredient compatibility and packaging all influence the stability of antioxidant formulations.

And remember, antioxidant ingredients don’t replace approved UV filters or justify sunscreen protection claims without appropriate testing.

Kojic Acid and Kojic Acid Dipalmitate: Targeting Uneven Skin Tone

Kojic Acid is primarily used in cosmetic formulations targeting the appearance of hyperpigmentation and uneven skin tone. Its activity is associated with interference in melanin production pathways.

However, Kojic Acid can present stability challenges, including discolouration and sensitivity to certain formulation conditions.

In the European Union, Kojic Acid is restricted to a maximum concentration of 1% when used as a skin-lightening agent in face and hand products.

Kojic Acid Dipalmitate is an oil-soluble derivative developed to offer different stability and formulation characteristics. However, the two ingredients aren’t interchangeable, and evidence supporting one cannot automatically be applied to the other.

Tranexamic Acid: An Acid That Doesn’t Exfoliate

Here’s another ingredient that frequently confuses beginner formulators! Despite its name, Tranexamic Acid isn’t used as a conventional exfoliating acid. Instead, it’s used in skincare formulations targeting uneven pigmentation and the appearance of dark spots.

It’s water-soluble, but its formulation requirements differ considerably from those of Glycolic Acid or Salicylic Acid.

Tranexamic Acid also has pharmaceutical applications, so cosmetic formulators must carefully evaluate ingredient status, intended use and product claims in their target markets.

Its presence in a cosmetic formula doesn’t automatically justify claims relating to the treatment of melasma or other medical conditions.

How to Choose the Right Acid for Your Cosmetic Formula

So, which acid should you choose? Well, that depends on what you’re trying to achieve!

If your goal is visible exfoliation and smoother skin texture, AHAs such as Glycolic Acid or Lactic Acid may be suitable.

For oily, blemish-prone skin, Salicylic Acid could be interesting.

If you’re developing a gentler exfoliating concept, PHAs such as Gluconolactone deserve consideration.

For uneven skin tone, you might investigate Azelaic Acid, Kojic Acid or Tranexamic Acid, depending on the formulation and regulatory requirements.

And if antioxidant protection is your priority, Ferulic Acid may be more relevant than an exfoliating acid.

But here’s my favourite formulation lesson: the best acid isn’t necessarily the strongest one. It’s the ingredient that performs appropriately within a well-designed, safe and stable formula. Before launching any acid-based cosmetic product, evaluate concentration, pH, solubility, skin tolerance, stability and applicable regulations.

And please, don’t forget the importance of appropriate product testing!

Final Thoughts: Understanding Acids Makes You a Better Cosmetic Formulator

Acids are fascinating cosmetic ingredients because their functions extend far beyond exfoliation.

Some help improve skin texture, others support hydration, while certain acids are particularly interesting for antioxidant protection or uneven skin tone.

Understanding these differences allows you to formulate with intention rather than simply following popular skincare trends.

And that’s what separates a beginner mixing fashionable ingredients from a cosmetic formulator who truly understands what they’re creating.

So, the next time you see an exciting new acid trending in skincare, don’t immediately add it to your shopping basket!

Explore its chemistry, understand its formulation requirements and decide whether it genuinely contributes to your product’s purpose.

Because beautiful cosmetic formulations begin with informed ingredient choices.

Here’s to formulas that work and brands that thrive!

From my lab to yours,

Rose