Alpha hydroxy acids (AHAs), beta hydroxy acids (BHAs), polyhydroxy acids (PHAs) and lipohydroxy acids (LHAs) are types of acid found in many chemical exfoliants. They all help remove dead skin cells from the top layer of the skin, but they work in different ways — and each has its own benefits, ideal use cases and customer profile.
For brands and retailers, the AHA/BHA/PHA/LHA category is one of the most-searched but worst-understood in skincare ecommerce. Customers know they want "an acid", but they don't know which one, in what strength, or how to layer it with the rest of their routine — and the consequence is a high rate of mismatched purchases, barrier damage, and abandoned baskets. This guide breaks down how each acid actually works, and where the merchandising and personalization gaps tend to sit.
How each acid works
- AHAs work on the surface layer of the skin to dissolve dead skin cells, which can even skin tone, improve radiance and target fine lines. Some also have hydrating properties.
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BHAs (best known as salicylic acid) have antibacterial properties and are oil-soluble, so they sink deeper into the skin to unclog pores, dissolve excess oil and prevent blackheads and breakouts.
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PHAs have a larger molecular structure than AHAs and BHAs, which means they take longer to penetrate and don't penetrate as deeply — working on the surface layer of the skin and making them more suitable for sensitive skin.
- LHAs are a derivative of salicylic acid that is much gentler than a standard BHA. They can be used more often than AHAs or BHAs, but work more slowly.
Common AHA, BHA, PHA and LHA ingredients
AHAs:
- Glycolic acid
- Lactic acid
- Mandelic acid
- Citric acid
BHAs:
- Salicylic acid (or related ingredients like willow bark extract)
PHAs:
- Gluconolactone
- Lactobionic acid
- Maltobionic acid
- Galactose
LHAs:
- Capryloyl salicylic acid
Matching the acid to the customer
These acids treat different skin challenges and are suited to different skin types:
- AHAs are best for less congested skin looking to improve radiance and even tone.
- BHAs work best for oilier skin that's prone to congestion.
- PHAs are better for sensitive skin types — including those with rosacea, eczema or compromised barriers.
- LHAs are best suited to combination or oilier skin prone to congestion, but may be too stripping for drier skin types.
Increasingly, brands are formulating combination products — AHA + BHA, or AHA + PHA — to target multiple concerns in one step. For customers, choosing a carefully formulated combination product is far less risky than mixing and matching different exfoliating acids on their own.
What this means for brands and retailers
Exfoliating acids are one of the highest-intent, highest-confusion categories in skincare. A customer typing "best acid for breakouts" into a search bar is signaling buying intent — but they're also signaling that they don't know what to choose. Three patterns we see across brand and retailer sites:
- Category pages are a wall of options. A customer with sensitive skin looking for a PHA gets shown the same lineup as a customer with oily, congested skin who needs a BHA. The information needed to choose correctly — skin type, sensitivity, what else is in their routine — isn't being captured.
- The wrong choice damages the relationship. A customer who buys a 10% glycolic acid serum when they should have started with a 5% lactic acid (or a PHA) will likely experience redness, dehydration or breakouts. They then conclude "this brand doesn't work for me" — when in fact, they were never sold the right SKU.
- Layering creates compounding risk. Acids combined incorrectly with retinoids, vitamin C or benzoyl peroxide cause significant barrier disruption. Customers can't reliably self-diagnose what's compatible with what they already own.
This is a category where personalization moves the needle measurably. Surfacing the right acid for the right customer — and flagging incompatible combinations against the rest of their routine — turns confusion into confident purchase.
Safe use guidance to embed in brand education
Whether through onsite content, product copy or AI-powered guidance, the core safe-use principles brands should communicate are:
- Phase in gradually. Start AHAs and BHAs 1–2 times per week and build up over several weeks. PHAs can be used 3–4 times a week from the start because they're gentler.
- Daily SPF is non-negotiable. All exfoliating acids increase photosensitivity. UVA and visible light penetrate windows, so even indoor days require protection.
- Patch test reactive skin. Apply a small amount behind the ear or on the inner wrist; if there's no reaction after 24 hours, proceed.
- Stop if the barrier is compromised. Redness, dehydration, itching or sudden breakouts are signs to pause active ingredients and focus on barrier repair.
What a dermatologist says
Dr Justine Kluk, Renude's consultant dermatologist, runs her own respected clinic on Harley Street and specializes in treating acne. She regularly recommends acids as part of clinical and at-home protocols.
"Exfoliating acids have become increasingly popular with skincare enthusiasts and those looking to improve their skin over the last couple of years. They are also one of the areas where there is most confusion. Potential pitfalls are being overzealous when starting out — too much too soon — and not being cautious about combining with other active skincare ingredients. My top tip: go slow when starting out and keep the rest of your routine gentle and simple."
For brands, the takeaway is that the customer needs guidance at the point of selection, not just a product description. Education and personalization are part of the product.
PHA vs LHA: which works for sensitive skin?
Both PHAs and LHAs are useful for sensitive skin because they are gentler and work more slowly than AHAs and BHAs. However, the right choice depends on the customer's broader skin profile:
- PHAs are preferred for dry skin, rosacea or eczema. Their larger molecular structure means they work only on the surface layers of the skin, making them more gentle. PHAs also help retain moisture and can deliver visible improvements in sun-damaged skin. They're safe to use during pregnancy.
- LHAs are oil-soluble, so they suit combination or oilier skin prone to congestion. They can be too stripping for drier skin because they dissolve the skin's natural oils. The right call also depends on the specific formulation and the rest of the routine.
How Renude helps brands sell acids more confidently
Renude's AI Skin Analysis and AI Skin Advisor are trained to identify a customer's skin type, sensitivity level and existing routine — then recommend the right acid (or combination) from your specific product catalog. The AI flags incompatible combinations, suggests appropriate starting frequencies, and answers ingredient-level questions in real time, so customers reach the right SKU with confidence instead of bouncing or guessing.
Across our brand and retailer deployments, Renude's AI delivers +150% AOV uplift (SVR), +63% conversion and +79% AOV (Ella & Jo), and a 91% email opt-in rate — turning one of skincare's most confusing categories into one of its highest-converting.
If you'd like to see how Renude could help your customers navigate exfoliating acids with confidence, book a demo.
