The ESK blog
What’s the difference between HA, AHAs and PHAs?
01 September 2026
Dr Anne Thomson
Written by Dr. Anne Thomson
Scientists and health professionals just love a good acronym. They can be pretty useful for abbreviating long, complicated names into quick little bites that get the message across quickly. But they sure can get confusing and certainly aren’t much use if no-one knows what they stand for!
If HA makes you think of a laughing emoji, and AHA makes you think of an 80’s band (apologies to our Gen X readers who now have ‘Take On Me’ stuck in their heads), then read on as we untangle the Acronym Alphabet Soup (AAS?) to reveal some of the most effective ingredients in skincare today.
HA AKA Hyaluronic Acid
Not actually an acid, HA is a complex sugar which occurs naturally throughout our bodies in places like our skin and joints.
In the skin, it is vital for supporting the extracellular matrix – or scaffolding - of the skin, literally holding it up. It does this by promoting collagen and elastin production, skin cell regeneration, wound healing and maintaining the skin’s hydration. In fact, it can attract and bind water molecules up to 1000 times its own weight. Handy!
As we age, our skin (and joints) start to lose HA so we start to see increasing dryness, more sensitivity, and of course a loss of skin elasticity and more fine lines and wrinkles.
What does it do in skincare?
We now have good emerging evidence that using HA in skincare can yield significant improvements in the skin’s overall appearance, with fewer fine lines and wrinkles, smoother skin and a big boost in hydration. It can even help with rosacea and seborrheic dermatitis.
You’ll find HA in several forms for at-home use: serums, creams and even in microneedle patches that can be used to deliver hydration and other active ingredients to targeted areas like around the eyes (crow’s feet).
Shop ESK Hyaluronic Acid Collection
Our Hydraboost Hyaluronic Acid Serum is designed to provide deep, lasting hydration with a blend of high, medium, and low molecular weight hyaluronic acids (HA). High molecular weight HA sits on the skin’s surface, creating a protective hydration layer that feels smooth and instantly refreshing. Meanwhile, low and medium molecular weight HA molecules sink deeper, boosting hydration within the skin barrier. Studies suggest that low molecular weight HA can reduce the appearance of wrinkles and fine lines. Lightweight and versatile, Hydraboost is perfect for daily use as the first step in your routine for plump, hydrated skin.
Hydraboost HA Serum
Featuring
- Enhanced daily skin hydration
- Plumper, healthier feeling skin
Turns out size does matter…
Not all HA is created equal however. Large molecular weight HA struggles to get through the skin but does hydrate and has anti-inflammatory properties. Low molecular weight HA, does penetrate the skin and better evidence for skin aging and repair but may cause irritation. Medium weight HA can penetrate the skin and seems to be well tolerated, but studies on its effectiveness are limited. The current evidence suggests that using a combination of High, Medium and Low molecular weight HA is best.
Which skin types is HA best for?
HA (combination of all weights) is usually well tolerated but if you have sensitive skin it is a good idea to patch test any product with Low molecular weight HA to be sure. But if you’re looking for a hydration boost, smoother and plumper skin, reduced fine lines and wrinkles and boosted collagen (OK who are we kidding, that is almost everyone) HA is definitely worth a look.
AHA AKA Alpha-hydroxy Acids
Now these really ARE acids, and if you’re new to skin care (welcome!), the idea of putting acid on your face might seem a little… nuts. But bear with us, because the evidence is well and truly in on these little powerhouses of the skincare world.
AHAs are naturally occurring fruit acids that are best known in skincare as chemical exfoliators; they work by loosening the bonds that hold the superficial layer of skin cells together, allowing these dull, rough cells to slough off which speeds up the renewal of the fresh skin cells below.
But they do so much more than just exfoliate. The two best studied AHAs are glycolic acid and lactic acid which have been shown to smooth the skin, reduce wrinkles, improve skin elasticity, tone and hydration. They can also flush out excess pigment (melanin). And they enhance the effects of other skin actives like retinal. Win-win!
Which skin types are AHAs best for?
AHAs have proven benefits against the signs of ageing like fine lines, wrinkles, pigmentation and rough, dry or dull skin. They have also been shown to be effective in acne. People with sensitive or rosacea-prone skin usually need to avoid them though due to the risk of irritation.
How to use AHAs
AHA’s in high concentrations are used for in-clinic peels – the concentration is typically around 20% and whilst effective, usually causes significant after-effects such as burning, redness, peeling, even swelling and blisters.
In concentrations below 5%, they can be used at home in cleansers or as leave-on serums or creams. They increase sensitivity to UV radiation so we recommend using them at night and always using a mineral sunscreen like zinc oxide during the day.
Smooth Serum is a night treatment formulated with 3% Glycolic acid, 1% Lactic acid, and 1% Gluconolactone. This gentle AHA blend supports the appearance of skin texture and surface renewal, helping maintain the look of even skin tone. Caution: Not recommended for very sensitive skin or skin prone to rosacea.
Smooth Serum
Key features:
Our Hydroxy Cleanser is a soap-free, pH-balanced cleanser that provides gentle yet effective cleansing for your skin. Lightly foaming, it removes dirt, excess oils, and impurities without drying or irritating, making it perfect for maintaining a healthy skin barrier. Designed with a neutral to acidic pH, it’s ideal for sensitive skin types, including those with acne, aging skin and pigmentation. This cleanser helps preserve hydration, supports the skin’s microbiome, and normalises skin pH, creating the perfect base for your skincare routine. Free from harsh soaps, astringents, and irritants, Hydroxy Cleanser leaves skin feeling fresh, balanced, and ready for any treatment. Featuring Gentle, soap free syndets to leave your skin feeling clean and soft A pH of 4.5-5 to maintain the skin barrier Perfect for daily use for normal/oily skin
Hydroxy Cleanser
PHAs AKA Poly-hydroxy Acids
PHAs are similar to AHAs in that they exfoliate and smooth the skin surface, but they are much more gentle than their AHA cousins. Like AHAs, they are chemical exfoliators, meaning they break the bonds between superficial dead skin cells allowing them to slough off revealing fresher newer skin underneath.
Also like the AHAs, they do so much more than just exfoliate. Studies have shown that they have antioxidant and moisturising properties. But they also improve the skin barrier function, help reduce pigmentation, and help build collagen by inhibiting the enzymes that break it down. Plus they combat acne.
But where they differ from AHAs is that they are super gentle and can be used in the most sensitive of skin types including rosacea skin.
The two best studied ones are lactobionic acid and gluconolactone. Because they are gentler, it can take a little longer for them to take effect. Like the AHAs, we recommend using them at night.
Introducing our breakthrough skincare solution, the Gentle Glow PHA Serum, designed specifically for those with irritable, red or dry skin! - Reduces the appearance of fine lines and wrinkles and the apparent size of pores. - Helps tackle blemishes and is appropriate for irritable and red skin.
Gentle Glow PHA Serum
Harnessing the power of Polyhydroxy Acids (PHAs), which gently exfoliate and smooth the skin's surface, act as antioxidants and hydrate the skin. Unlike most exfoliation agents, PHAs are very gentle and are not only tolerated on irritable skin, but may also reduce potential irritation from other products in your skincare regimen!
Embrace the journey to a luminous, glowing complexion with the Gentle Glow PHA Serum.
- Smooths, hydrates and plumps the skin.