What Are Hydroxy Acids? AHA, BHA And PHA Explained

Understanding hydroxy acids in skincare can make choosing an exfoliant much easier. These ingredients are used in cleansers, toners, serums, masks and at-home peels to help remove dull surface build-up and improve the look and feel of uneven skin texture. The best-known groups are alpha hydroxy acids, or AHAs, beta hydroxy acids, or BHAs, and polyhydroxy acids, known as PHAs.

Although all three groups are associated with exfoliation, they are not interchangeable. The type of acid, concentration, pH, overall formulation, whether the product is rinsed off or left on the skin, and how often it is used can all affect how a product performs and how well your skin tolerates it.

What Are Hydroxy Acids?

Hydroxy acids are a broad group of ingredients used in skincare and professional treatments. Rather than physically scrubbing the skin, exfoliating acids help loosen the connections between older cells at the surface so they can shed more readily.

This can leave skin feeling smoother and may improve the appearance of dullness, uneven texture and some types of visible congestion. Results depend on the particular acid and formulation, so stronger is not automatically better.

Hydroxy acids are used both in everyday cosmetic products and in stronger professional chemical peels. These are not the same thing. Professional peels can use different concentrations, combinations and application methods and should be carried out according to professional protocols rather than copied at home.

What Are Alpha Hydroxy Acids?

Alpha hydroxy acids, usually shortened to AHAs, are water-soluble acids commonly used to exfoliate the surface of the skin. Two of the best-known examples are glycolic acid and lactic acid.

Common AHAs used in skincare include:

• Glycolic acid
• Lactic acid
• Mandelic acid
• Citric acid
• Malic acid
• Tartaric acid

Glycolic acid has a relatively small molecular size and is widely used in products designed for dullness, rough texture and uneven-looking tone. Lactic acid is another established AHA and is also associated with moisturising properties within suitable formulations.

The older version of this article listed where each acid supposedly comes from, such as milk, apples or grapes. That can be misleading because cosmetic ingredients may be manufactured or sourced in different ways. An ingredient's name does not necessarily tell you how the acid in a particular finished product was produced.

Is Phytic Acid An AHA?

No. Phytic acid is sometimes discussed alongside AHAs because it is used in exfoliating and brightening skincare formulas, but chemically it is not an alpha hydroxy acid.

It may still be included alongside glycolic, lactic, salicylic or other acids in a multi-acid formula. Dermalogica Liquid Peelfoliant, for example, combines glycolic and lactic AHAs, salicylic acid, the PHA gluconolactone, phytic acid, tranexamic acid and a fermented pomegranate enzyme.

This is a useful example of why it is better to look at the whole formula rather than assuming every ingredient described as an acid belongs to the same family.

What Are Beta Hydroxy Acids?

In skincare, BHA usually refers to salicylic acid. Unlike water-soluble AHAs, salicylic acid is oil-soluble, which allows it to work effectively in oilier areas of the skin and within the environment of pores.

This makes salicylic acid particularly useful in products designed for oily, congested or breakout-prone skin and for the appearance of blackheads and blocked-looking pores.

The old description of salicylic acid acting like a "corkscrew" and diving into pores is not a useful scientific explanation. A simpler way to understand it is that its oil solubility makes it well suited to exfoliating where excess sebum and surface build-up are present.

Salicylic acid is used in many different product types, including cleansers and leave-on treatments. The concentration and contact time differ considerably between them, so a salicylic acid cleanser should not automatically be compared directly with a leave-on serum based only on the percentage shown on the label.

What Are Polyhydroxy Acids?

PHAs, or polyhydroxy acids, are another group of exfoliating acids. Examples include gluconolactone and lactobionic acid.

They are often formulated as a gentler alternative to more traditional AHAs. PHAs have larger molecular structures than ingredients such as glycolic acid and have also been studied for their moisturising and skin-conditioning properties.

This does not mean every PHA product will automatically suit sensitive skin. The complete formula still matters, and anyone with very reactive skin should introduce exfoliating products carefully.

AHA Vs BHA Vs PHA: Which Should You Choose?

There is no single acid that is best for everyone.

• AHAs: Often chosen when dullness, rough texture or uneven-looking tone are the main concerns.
• BHA: Salicylic acid is commonly used when excess oil, visible congestion and blackheads are concerns.
• PHAs: Often used when someone wants surface exfoliation but prefers a formula designed with gentler exfoliation in mind.

Your skin type alone does not determine the answer. The strength of the product, frequency of use and what else is already in your routine can matter just as much.

Does A Higher Acid Percentage Mean Better Results?

No. Percentage is useful information, but it does not tell you everything about how strong or suitable a product will feel.

Factors that can influence the effect of an exfoliating acid include:

• The type of acid
• The concentration
• The pH of the finished formula
• Whether the product is rinsed off or left on
• How long it remains on the skin
• The other ingredients in the formulation
• How frequently you use it
• Your own skin tolerance

This is why comparing two products purely by choosing the one with the highest percentage is not a reliable way to decide which is more suitable.

Does Tingling Mean An Acid Is Working?

Not necessarily. A mild temporary tingling sensation can occur with some exfoliating products, particularly stronger formulas, but discomfort is not a measure of effectiveness.

Persistent burning, significant redness, swelling or prolonged irritation should not be treated as evidence that the product is doing a better job. If a product repeatedly irritates your skin, reduce the frequency or stop using it and follow the manufacturer's directions.

Your skin does not need to feel sore or visibly peel for exfoliation to be effective.

Can You Use Several Acids At The Same Time?

Some finished products are deliberately formulated with more than one acid, and these can be perfectly reasonable to use according to their instructions. Problems are more likely to occur when several separate exfoliating products are layered together without considering the combined effect.

For example, using an exfoliating cleanser, leave-on acid toner, strong peel and retinoid in the same routine may be more than your skin needs.

If you are introducing acids for the first time, start with one exfoliating product and see how your skin responds before adding another. A simpler routine can make it much easier to identify what is helping and what may be causing irritation.

How Often Should You Use Hydroxy Acids?

There is no universal schedule. Some products are designed for daily use, while stronger treatments may be intended for only a few applications each week.

Follow the directions for the individual product and pay attention to how your skin feels. If you notice increasing tightness, burning, flaking or persistent sensitivity, using more exfoliant is unlikely to help.

It can be sensible to reduce the frequency of acids when introducing other active ingredients, particularly retinoids or additional exfoliating treatments.

Do Hydroxy Acids Make Skin More Sensitive To The Sun?

AHAs such as glycolic and lactic acid can increase sensitivity to ultraviolet radiation while they are being used. Research reviewed by the US Food and Drug Administration found that this effect can continue for a short period after stopping an AHA product.

Sun protection is therefore particularly important when AHAs form part of your routine. In the UK, NHS guidance recommends choosing sunscreen with at least SPF30 and at least four-star UVA protection, alongside sensible use of shade and protective clothing when needed.

Sun protection is worthwhile throughout the year regardless of whether you use exfoliating acids.

Current Hydroxy Acid Products At John And Ginger

If you want to introduce acids into your routine, choose the product according to what your skin needs rather than trying to use every type at once. These are current examples from the John And Ginger range.

Dermalogica Daily Glycolic Cleanser 150ml

Dermalogica Daily Glycolic Cleanser 150ml is an AHA cleanser containing glycolic acid. It is designed to cleanse while helping dull and uneven-looking skin appear smoother and brighter.

Dermalogica Skin Resurfacing Cleanser 150ml Pump

Dermalogica Skin Resurfacing Cleanser 150ml Pump uses lactic acid in an exfoliating cleanser designed for skin concerned with dullness, rough texture and visible signs of ageing.

Dermalogica Clearing Skin Wash 250ml

Dermalogica Clearing Skin Wash 250ml contains salicylic acid and is designed for oily and combination skin that is prone to visible congestion and breakouts.

Dermalogica Daily Liquid Peelfoliant 59ml

Dermalogica Daily Liquid Peelfoliant 59ml is a stronger rinse-off treatment combining AHAs, salicylic acid, the PHA gluconolactone, other acids and enzymes. Dermalogica recommends introducing it gradually and monitoring how your skin responds.

Dermalogica Daily Microfoliant Exfoliator 74g

Dermalogica Daily Microfoliant Exfoliator 74g is a rice-based powder exfoliant containing salicylic acid alongside papain, rice enzymes and other ingredients. Its current size is 74g, rather than the 75g size referred to in the older version of this article.

Dermalogica Age Bright Clearing Serum 30ml

Dermalogica Age Bright Clearing Serum 30ml is a lightweight leave-on serum containing 2% salicylic acid. It is designed for adult breakout-prone skin where visible congestion and uneven-looking tone are concerns.

You can also browse our wider AHA and BHA skincare range if you want to compare acids across different brands and product types.

What About Professional Chemical Peels?

Professional chemical peels should be treated separately from everyday home exfoliation. Dermalogica's current Pro Power Peel professional treatment uses a combination of acids including glycolic, lactic and salicylic acid, with treatment selected and adjusted by a trained professional.

Professional peel concentrations and protocols should not be recreated using several home products together. If you are considering a professional peel, follow the pre-treatment and aftercare guidance provided by the practitioner carrying out your treatment.

When Should You Be More Cautious With Acids?

Be cautious if your skin is already irritated, damaged, sunburnt or reacting to another product. Exfoliating more is unlikely to solve a compromised or uncomfortable skin barrier.

You should also seek appropriate advice before adding strong exfoliating acids if you are using prescription skincare or treatments that already affect skin renewal. If you have moderate or severe acne, painful spots, nodules or scarring, the NHS recommends speaking to a GP rather than relying solely on cosmetic skincare.

People with very reactive skin, rosacea, eczema or another diagnosed skin condition may find acids irritating, particularly during a flare-up. Skincare cannot replace medical treatment for these conditions.

Keeping An Acid Routine Simple

Hydroxy acids can be useful when they are chosen for a clear reason and used at a frequency your skin tolerates. You do not need an acid cleanser, toner, serum and peel all in the same routine.

Start with the concern you actually want to address. An AHA may suit a routine focused on dullness and rough texture, salicylic acid may be useful for visible congestion and oily areas, while a PHA-containing product may appeal if you want a gentler approach to surface exfoliation.

Whichever type you choose, follow the product directions, moisturise when your skin needs it and use appropriate sun protection during the day. Comfortable, consistent use is more useful than chasing the strongest formula available.