50ml full size, 15ml travel size
ESK · AHA night serum
Smooth Serum
ESK Smooth Serum · an AHA night serum with glycolic acid 3%, lactic acid 1% and a PHA
A night serum built on glycolic acid 3%, lactic acid 1% and gluconolactone 1% at pH 3.5 to 4, for the look of smoother texture, surface renewal and a more even tone. ESK's stronger exfoliating serum, for skin that is not very sensitive or rosacea-prone. Suitable for deeper skin tones (Fitzpatrick V to VI), introduced gradually.
- Glycolic acid 3% with lactic acid loosens dead surface cells so skin looks smoother and brighter; ESK notes glycolic acid also helps a retinal work.
- Gluconolactone (PHA) softens the blend and adds hydration.
- Night only, after cleansing and before your night cream. Start every second night.
- Not for very sensitive or rosacea-prone skin, per ESK: choose Gentle Glow. Daily SPF is essential. Contains essential oils.
New to acids? Try the 15ml first for £35
The travel size lasts 3 to 4 weeks at every-other-night use, which is long enough to know whether a glycolic serum suits your skin. If it stings, Gentle Glow is the PHA alternative.
Free UK delivery over £65 · Tracked £3.49 · Sent tracked, 2 to 4 working days
- Good to know
- Contains essential oils (rose, geranium, lavender, lemon myrtle) and witch hazel water. Glycolic acid increases sun sensitivity: daily SPF is essential.
- Stockist
- Melatone Skin Clinic is an authorised ESK stockist. Genuine product with full traceability.
If it stings for more than a few seconds, or your skin goes red or flaky, stop, and switch to Gentle Glow. On deeper skin tones, irritation from an acid can leave marks, so do not push through. Message us.
Not sure if this is right for your skin? Message us on WhatsApp or book a skin assessment and we will confirm the right routine first.
A glycolic acid serum, honestly
Most people who reach for it have skin that looks dull or feels rough, with the uneven tone that dead surface build-up leaves, and want something that works faster than a PHA. That is what glycolic acid does: the smallest AHA, it loosens the bonds holding dead cells on the surface, so skin looks smoother and brighter within weeks.
What it will not do is suit everyone. ESK is explicit that it is not for very sensitive or rosacea-prone skin, and it contains essential oils. It also makes skin more sensitive to the sun for as long as you use it, so it is a night product with a non-negotiable SPF the next morning.
On deeper skin tones, an acid used too often is one of the classic causes of dark marks. Used every second night, built up slowly, under SPF, a 3% glycolic serum is well within what most skin tolerates; rushed, it is not. Gentle Glow is the safer first step if your skin has ever marked after irritation.
Quick facts
- What it is
- An AHA exfoliating night serum.
- Sizes
- 50ml (£69.00, around 3 to 4 months) and 15ml travel size (£35.00, around 3 to 4 weeks).
- Best for
- The look of rough texture, dullness and uneven tone; normal, combination and oily skin.
- Skin types
- All skin types except very sensitive or rosacea-prone, per ESK. Suitable for deeper skin tones (Fitzpatrick V to VI), introduced slowly.
- Key ingredients
- Glycolic acid 3%, lactic acid 1%, gluconolactone 1%, witch hazel water, hyaluronic acid.
- pH
- 3.5 to 4.0.
- How to use
- 1 to 2 pumps, night only, after cleansing and before your night cream. Start every second night.
- Daily SPF
- Essential. AHAs increase sun sensitivity.
- Free from
- Parabens and sulphates. Non-comedogenic. Contains essential oils.
- Pregnancy
- Ask your midwife, GP or pharmacist before using a leave-on acid.
Where it fits in a night routine
Night: cleanse, Smooth Serum, then your night cream. With a retinal such as Ultimate A Gold, ESK says the glycolic acid works well alongside the retinal unless you get irritation; introduce them on separate nights first.
Morning: cleanse, your day moisturiser, then SPF such as Zinc Shade. Never skip it while using an acid.
If your skin is sensitive or rosacea-prone: Gentle Glow is the PHA version of this step, and the one in the Rosacea Kit. For congestion with a retinal built in, Ultimate A+.
The detail
Ingredients, and what each one does
- Glycolic acid (AHA), 3%
- The smallest AHA. Loosens the bonds between dead surface cells so they shed, for smoother, brighter-looking skin, and ESK says it increases the effectiveness of retinal. Increases sun sensitivity. Widely studied.
- Lactic acid (AHA), 1%
- A slightly larger AHA with gentler surface exfoliation and some hydrating action. Widely studied.
- Gluconolactone (PHA), 1%
- A large-molecule acid that exfoliates gently and hydrates, softening the blend. Widely studied.
- Witch hazel water, bamboo and saffron extracts
- Traditional skin-conditioning botanicals.
- Hyaluronic acid (sodium hyaluronate), glycerin
- Humectants that offset the drying effect of the acids.
- Menthyl lactate
- A cooling agent that gives the serum its fresh feel on application.
- Essential oils
- Rose, geranium, lavender and lemon myrtle, carrying the fragrance allergens linalool, citronellol, geraniol and citral, listed on the label.
Glycolic acid 3%, lactic acid 1% and gluconolactone 1% as printed on the ESK pack; pH 3.5 to 4.0 as published by ESK. Descriptions are about the look and feel of skin, not a medical outcome.
Full ingredients (INCI): Aqua, Alcohol, Hamamelis Virginiana Water, Glycolic Acid, Glycerin, Gluconolactone, Bambusa Vulgaris Leaf/Stem Extract, Butylene Glycol, Coceth-7, Crocus Sativus Stigma Extract, Menthyl Lactate, PEG-40 Hydrogenated Castor Oil, PPG-1-PEG-9 Lauryl Glycol Ether, Lactic Acid, Hydroxyethylcellulose, Benzyl Alcohol, Chondrus Crispus Extract, Dehydroacetic Acid, Rosa Damascena Flower Oil, Orchis Mascula Extract, Phenoxyethanol, Linalool, Citronellol, Pelargonium Graveolens Flower Oil, Lavandula Angustifolia Oil, Geraniol, Citral, Benzoic Acid, Sodium Benzoate, Sodium Hyaluronate, Backhousia Citriodora Leaf Oil.
How to use it
Night
- Cleanse and pat dry.
- Put 1 to 2 pumps of Smooth Serum on your fingertips and smooth over the face, avoiding the eye area.
- Let it settle for a minute.
- Follow with your night cream or retinal.
Building up
Week 1: every second night. Then nightly if your skin is comfortable, per ESK. Stinging, redness or flaking means hold at every second night, or step down to Gentle Glow.
Beyond the face
It can also be used on the décolletage, the backs of the hands and the forearms.
Morning
Broad-spectrum SPF every day, without exception. AHAs make the skin more sensitive to UV.
What to expect, and when
- First use
- A brief cooling tingle from the menthyl lactate is normal. Stinging that lasts is not.
- 1 to 2 weeks
- Skin feels smoother and looks brighter.
- 4 to 6 weeks
- The point to judge texture and the look of surface tone.
- 8 to 12 weeks
- The point to judge marks and uneven tone. If nothing has changed, reassess with us rather than buying another bottle. Message the clinic.
Is it right for my skin
- Normal and combination skin
- Yes.
- Oily and congested skin
- Yes. Ultimate A+ is the alternative with a retinal built in.
- Dull or rough-feeling skin
- Yes. This is the core use.
- Uneven tone and marks
- Yes, alongside SPF and a tone-evening active.
- Deeper skin tones (Fitzpatrick V to VI)
- Yes, introduced slowly, every second night, under daily SPF.
- Very sensitive or rosacea-prone skin
- No, per ESK. Choose Gentle Glow.
- Fragrance-sensitive skin
- Patch test first: it contains essential oils.
- Pregnancy or breastfeeding
- Ask your midwife, GP or pharmacist before using a leave-on acid.
Using it with what you already own
- Retinal (Ultimate A, A+, A Gold)
- ESK says glycolic acid enhances retinal, so the two can be used together unless you get irritation. Start them on alternate nights.
- Vitamin C
- Yes: vitamin C in the morning, Smooth Serum at night.
- Enlighten Gold
- Yes. Smooth Serum first, then Enlighten Gold as your night cream.
- Other acids (Gentle Glow, salicylic leave-ons)
- Do not stack them at night. One exfoliating serum is enough.
- Hydroxy Cleanser
- Fine: it is rinsed off. If skin gets dry, cleanse with it once a day.
- After in-clinic treatments
- Pause it for as long as your practitioner advises after a peel, microneedling or laser.
Questions we actually get asked
What is ESK Smooth Serum?
A night serum with glycolic acid 3%, lactic acid 1% and gluconolactone 1% at pH 3.5 to 4, for the look of smoother texture and more even tone. It is ESK's stronger exfoliating serum; Gentle Glow is the gentler PHA version.
What does glycolic acid do for skin?
Glycolic acid is the smallest alpha hydroxy acid. It loosens the bonds between dead cells on the skin's surface so they shed more evenly, which makes skin look smoother and brighter and helps the look of uneven tone. It also increases sun sensitivity, so SPF is essential.
Glycolic acid or PHA: which should I use?
Glycolic acid is faster and stronger; a PHA (gluconolactone, lactobionic acid) is gentler, larger-molecule and hydrating. Very sensitive or rosacea-prone skin, or skin that has marked after irritation before, should start with the PHA: Gentle Glow. Everyone else can use Smooth Serum.
How do I use a glycolic acid serum?
At night, on clean dry skin, 1 to 2 pumps over the face, then your night cream. Start every second night for the first week, then nightly if your skin is comfortable. SPF every morning.
How often should I use it?
ESK: every second night for a week, then nightly if tolerated. Many people settle at 3 to 4 nights a week, which is fine.
Can I use glycolic acid with retinol or retinal?
ESK says the glycolic acid in Smooth Serum enhances the effectiveness of retinal, so yes, unless you get irritation. Introduce them on alternate nights, then combine if your skin is comfortable.
Can I use it with vitamin C?
Yes: vitamin C in the morning, Smooth Serum at night.
Can I use it with niacinamide?
Yes. B Calm, Repair + or Enlighten Gold can go over it as your night cream.
Can I use it in the morning?
No. ESK does not recommend daytime use, to limit photosensitivity. Keep it for night and wear SPF the next morning.
Does glycolic acid help with acne?
It helps keep dead cells from building up, which supports congested skin, and it is studied for the marks left after spots. For breakouts themselves, salicylic acid (Hydroxy Cleanser, B Calm) is the usual choice, and Ultimate A+ combines glycolic acid with a retinal.
Does glycolic acid lighten skin?
No. It does not change your natural skin colour. It helps the look of dullness and uneven tone by removing dead surface cells, which is a different thing.
Will it help dark marks?
Regular exfoliation supports the look of surface marks, and glycolic acid is used for that. Pair it with daily SPF and, for marks as the main concern, a tone-evening active such as Enlighten Gold.
Is it suitable for sensitive skin?
No. ESK does not recommend it for very sensitive or rosacea-prone skin. Gentle Glow is the exfoliant for that skin.
Is it suitable for deeper skin tones?
Yes. It is suitable for deeper skin tones (Fitzpatrick V to VI), introduced every second night and under daily SPF. On deeper skin, an acid rushed is a classic cause of dark marks, so the build-up matters.
Does it tingle?
A brief cooling tingle from the menthyl lactate is normal on application. Stinging that lasts, or redness afterwards, means it is too strong for your skin right now.
Can I use glycolic acid while pregnant?
Ask your midwife, GP or pharmacist before using a leave-on acid in pregnancy or breastfeeding. ESK publishes no specific guidance for Smooth Serum.
Do I need SPF with it?
Yes, every morning, without exception. AHAs make skin more sensitive to UV for as long as you use them.
Does it contain fragrance?
It contains natural essential oils, rose, geranium, lavender and lemon myrtle, and lists the fragrance allergens linalool, citronellol, geraniol and citral. If you react to fragrance, patch test first or use Gentle Glow, which has none.
What is the difference between Smooth Serum and Gentle Glow?
Smooth Serum is an AHA serum (glycolic 3%, lactic 1%) with a little PHA, faster and stronger, with essential oils. Gentle Glow is a PHA serum (gluconolactone 5%, lactobionic acid 5%), gentler and hydrating, fragrance-free, for sensitive and rosacea-prone skin.
What is the difference between Smooth Serum and Ultimate A+?
Smooth Serum is an acid serum with no vitamin A. Ultimate A+ is a retinal night cream with 2% glycolic acid built in, for oily and congested skin. Do not use both on the same night without building up first.
How long does a bottle last?
The 50ml lasts around 3 to 4 months of nightly use, and longer at every second night. The 15ml travel size lasts around 3 to 4 weeks.
Is it cruelty free and vegan?
Yes. ESK states that Smooth Serum is cruelty free and vegan.
Is Melatone an authorised ESK stockist?
Yes. Melatone Skin Clinic is an authorised ESK stockist. Stock comes directly from ESK, so every item is genuine and traceable, and it is the same product we use in clinic.
Can someone help me work out whether this is right for me?
Yes. Message us on WhatsApp with a description of your skin, or book a skin assessment at the clinic in Battersea.
What is the delivery and returns position?
Tracked UK delivery is £3.49, or free over £65, and usually arrives in 2 to 4 working days. Sealed, unopened items can be returned within 60 days for a refund.
Buying it from Melatone
Melatone Skin Clinic is an authorised ESK stockist. Stock is bought directly from ESK, so every item is genuine and traceable, and it is the same product we use in clinic in Battersea, London.
If you are not sure this is the right exfoliant for your skin, do not guess. Message us on WhatsApp or book a skin assessment, and we will suggest a routine before you buy.
Delivery
Tracked UK delivery, £3.49 or free over £65. It usually arrives within 2 to 4 working days, with tracking by email. The price you see is the price you pay, with any delivery charge shown in full before checkout.
Returns
Sealed, unopened items may be returned within 60 days of receiving your order for a refund. For hygiene reasons we cannot accept returns of skincare once any seal has been opened, unless faulty. Your statutory 14-day right to cancel is unaffected.