AHA and BHA get all the attention. There's a third family on the shelf that rarely gets explained, and it's arguably the most useful one if your skin is easily upset: the polyhydroxy acids, or PHAs.
The short answer: PHAs deliver effects similar to alpha hydroxy acids but cause less irritation.[1] They achieve that through size — PHA molecules are much larger than other exfoliating acids, so they enter skin more slowly, which makes them gentler and a good option for sensitive skin.[2]
What actually makes an acid a PHA
The name is more descriptive than it sounds. Polyhydroxy acids are acids that carry two or more hydroxyl groups on their molecular structure.[1] Those extra groups make the molecule bigger and change how it behaves once it meets skin.
The one you'll actually encounter is gluconolactone — the most widely marketed polyhydroxy acid.[1] If a product lists a PHA, gluconolactone is usually what's meant.
Bigger molecule, slower entry, less sting
This is the mechanism in one line, and it's the same principle that makes mandelic acid gentler than glycolic acid — just taken further.
A small acid molecule enters skin quickly. Quick entry means a faster drop in local pH and a greater chance of stinging. PHA molecules are much larger, so they enter more slowly, and that slower entry is exactly why they're better tolerated.[2]
Crucially, slower doesn't mean ineffective. PHAs deliver effects comparable to AHAs — they simply get there without the same irritation.[1]
The evidence for "gentler but just as good"
This is the claim you most want tested, so it's worth saying what the evidence does and doesn't show.
In a 12-week head-to-head comparison of consumer skincare regimens, a larger-molecule PHA regimen was better tolerated than an AHA regimen while delivering comparable skin-smoothing benefit.[3] That's the strongest direct support for the proposition, and it used consumer-strength products over a realistic timeframe rather than in-clinic peels.
One caveat worth stating plainly: that study was conducted by authors affiliated with a company that markets PHA products, testing their own range.[3] The finding is consistent with everything the molecular-size science predicts, but it isn't independent, and it would be overstating things to present it as settled.
Where PHAs sit against the other two families
| Molecule size | Solubility | Best suited to | |
|---|---|---|---|
| AHA (glycolic, mandelic) | Small to large | Water (mandelic partly oil) | Surface texture and tone |
| BHA (salicylic) | Small | Oil | Congestion, surface oil |
| PHA (gluconolactone) | Largest | Water | Sensitive, easily irritated skin |
Most well-built exfoliants use more than one, because they work at different depths and suit different concerns. A PHA is often the component that makes a blend tolerable for daily use.
Who PHAs particularly suit
- Skin that stings at other acids. The slower entry is the entire point.
- Skin that's already dry or reactive. PHAs are commonly used in products aimed at sensitive skin.[4]
- Anyone new to exfoliating acids. A sensible place to start before deciding whether you need something faster.
- Skin in a demanding climate. Constant heat, humidity and air-conditioning leave less margin for a harsh product.
Where this shows up in the Cetaphil SA range
Gluconolactone is one of three acids in the Cetaphil SA blend, alongside salicylic acid and mandelic acid — three different molecule sizes working at three different depths.
The Cetaphil Gentle Exfoliation SA Lotion is suitable for sensitive skin and gentle enough for everyday use, helps strengthen and protect the skin barrier, and leaves skin softer and smoother after just one use. It also offers a progressive decrease in skin sensitivity over time — and in clinical testing it was proven to reduce skin sensitivity by 55% in 7 days.[5]
The Cetaphil Gentle Exfoliating SA Cleanser uses the same approach in a rinse-off format, and is suitable for daily exfoliation, even for sensitive skin.
Frequently asked questions
Are PHAs weaker than AHAs?
Slower rather than weaker. In a head-to-head consumer comparison, a PHA regimen delivered comparable smoothing benefit while being better tolerated.[3]
Can I use a PHA every day?
Many PHA-containing products are formulated for daily use. As with any acid, build up gradually rather than starting at maximum frequency.
Is gluconolactone the only PHA?
It's the most widely marketed one.[1] Lactobionic acid is another you may see on labels.[1]
Do PHAs make skin sun-sensitive?
Sun protection is sensible with any exfoliating acid, and in Singapore daily sunscreen is the baseline regardless of what else you use.
Should I use a PHA instead of an AHA or BHA?
Usually alongside rather than instead. Each family reaches a different depth and addresses a different concern, which is why blends exist.
The takeaway
PHAs are the largest exfoliating acid molecules, and that size is precisely why they're the gentlest — slower entry, less stinging, comparable results. Gluconolactone is the one you'll meet in practice. If acids have stung you before, a PHA-containing formula is the sensible next thing to try, built up gradually and paired with daily sunscreen. If your skin stays irritated despite a gentle routine, see a doctor or dermatologist.
Product information: Cetaphil Gentle Exfoliating SA Cleanser · Cetaphil Gentle Exfoliation SA Lotion
References
- Zhang C, et al. "Applications of hydroxy acids: classification, mechanisms, and photoactivity."
- Tang SC, Yang JH. "Dual Effects of Alpha-Hydroxy Acids on the Skin." Molecules.
- Green BA, Edison BL, Sigler ML. "A polyhydroxy acid skin care regimen provides antiaging effects comparable to an alpha-hydroxy acid regimen." Cutis.
- Ablon G. "Hydroxy Acids." Journal of Clinical and Aesthetic Dermatology, 2023.
- Based on consumer self-assessment. Galderma data on file.