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By Mari, founder of K Skin Aura · Updated 19 October 2026
The short answer
WHICH RETINAL STRENGTH SHOULD YOU START WITH?
If you have never used a retinoid, start low. A retinal serum can state its strength as a percentage or in ppm (parts per million), and 25 ppm is 0.0025% while 0.1% is 1,000 ppm, so those two sit 40 times apart. A bigger number is not a better product, and it does not tell you how your skin will feel. Start with the lower one, follow the directions on the pack, and wait if your skin is irritated today.
This guide is about cosmetic retinal serums. Prescription retinoids such as tretinoin follow your prescriber's instructions, and nothing here changes them.
What does the number on a retinal label mean?
Most people I talk to don't know, and I don't blame them, because brands don't make it easy. The figure is the share of the formula that is retinal. Some brands print a percentage, others print ppm. It is the same measure on two different scales.
- 25 ppm = 0.0025%
- 1,000 ppm = 0.1%
- 10,000 ppm = 1%
In our range, the Purito TXA 6% + Niacinamide 10% + Retinal Serum is 25 ppm. The Celimax Vita-A Retinal Shot Tightening Booster is listed at 0.1% retinal, which is 40 times the concentration of the Purito.
That tells you how much retinal is in the bottle. It does not tell you how your skin will respond, and it does not rank which product is better.
Is a higher number better?
Not by default. The Purito also contains 6% tranexamic acid and 10% niacinamide, so it is a different formula, not a weaker copy of the Celimax. The Celimax has niacinamide, panthenol and adenosine alongside its retinal. Either can suit or upset a given skin, and the retinal number can't capture that.
What matters more is your own skin: how reactive it is, how settled your barrier feels this week, and what else you use. And if a gentle strength keeps your skin comfortable and you are happy with it, no rule says you have to move up.
I don't know of a dermatology source that sets one correct starting strength for everyone, so I won't pretend there is one. What I can share is how I'd decide.
Which one is for you?
Here is how I'd think about it, in plain terms.
A lower retinal concentration is where I'd usually start if:
- It is your first retinoid.
- You used something stronger before, stopped because of irritation, and want to try again carefully.
- Your skin reacts easily.
The Purito's 25 ppm serum is one option, provided its full formula suits your skin. It also contains 6% tranexamic acid and 10% niacinamide, so check the ingredients and go gently.
A higher strength, such as the Celimax at 0.1%, is worth considering if:
- You have used a retinoid before and your skin took it calmly.
- Your skin has stayed comfortable on a gentler retinal for a few months, with no regular dryness, stinging or redness.
- You want more than you are getting, and you have checked that your sunscreen and moisturiser are doing their job first.
Wait, and don't start either, if:
- Your skin is stinging, tight, flaky or red right now. A retinal is the wrong thing to add to skin that is already irritated. Let it settle first.
- You are pregnant or breastfeeding, or you use a prescription retinoid. Ask your pharmacist or prescriber.
If you are happy where you are, staying there is a good answer.
A higher strength is not automatically the next step, and I won't invent a timeline for it.
Why I say start small
On Instagram you will find videos of people applying a thick layer of retinal over their face, and Celimax's booster comes up often. That is not how a retinal is meant to be used. More product is more likely to give you a sore, red face than a better result, and a little goes a long way.
My rule is simple: start small, and follow the directions on the pack. Your skin is not somewhere to experiment with stronger products just for the sake of it, and a damaged barrier takes far longer to repair than it does to upset.
What I'd have around it
Retinal is usually used in the evening, and what you use alongside it can make a real difference to how comfortable your skin feels. Supporting products can help, but they cannot guarantee that a retinal won't irritate your skin. Here is the least I'd use. Nothing more is needed.
Evening
- Cleanse gently. Nothing that leaves your skin squeaky.
- Retinal, a small amount, following the pack's directions.
- Calming serum, if you are using one.
- Moisturiser.
Morning
- Rinse, or cleanse gently.
- Calming serum, if you are using one.
- Moisturiser, if your skin wants it.
- Sunscreen. This is the step I'd never skip, because retinal makes daily sunscreen matter more.
If you already own a moisturiser and a sunscreen your skin likes, use those and spend nothing. That is the free option, and it is often the right one.
If you are choosing, these are the three I'd reach for.
A barrier moisturiser. Aestura AtoBarrier365 Cream is a rich cream with ceramides, cholesterol and fatty acids, with no fragrance in the listed ingredients. It is the one I'd put on top of a retinal on dry or sensitive skin, because it is built to keep moisture in. It does contain dimethicone, so skip it if you avoid silicones, and if your skin is oily a lighter gel cream will suit you better.
A calming serum, if your skin is reactive. Purito Wonder Releaf Centella Serum Unscented goes on before your moisturiser. I use it morning and evening. In the evening it goes on after my retinal and before my Aestura cream. In the morning I apply it after my azelaic acid and before my cream. It has centella, niacinamide, panthenol and ceramide NP, with no fragrance or essential oils. I'd call it a nice-to-have. If your skin is calm and your moisturiser is doing the job, you can leave it out. If your skin tends to feel stressed, it is the first thing I'd add.
A sunscreen that doesn't feel like a chore. If you need one, Purito Wonder Releaf Centella Daily Sun Lotion SPF50+ PA++++ is light, leaves no white cast and finishes dewy. It uses chemical filters, so if you prefer mineral, ask us and I'll point you to one. The best sunscreen is the one you will put on every morning.
Everything in this guide, and where it fits
Lower-strength retinal
Purito TXA 6% + Niacinamide 10% + Retinal Serum25 ppm retinal, with 6% tranexamic acid and 10% niacinamide. Where I'd usually start if it's your first retinoid. £18.99.
Higher-strength retinal
Celimax Vita-A Retinal Shot Tightening Booster0.1% retinal, with niacinamide, panthenol and adenosine. 40 times the concentration of the Purito. £18.00.
Barrier cream for the evening
Aestura AtoBarrier365 CreamThe cream I put on after my retinal, even though my skin is combination and sensitive. Ceramides, cholesterol and fatty acids to keep moisture in. £28.99.
Calming serum
Purito Wonder Releaf Centella Serum UnscentedCentella, niacinamide, panthenol and ceramide NP, with no fragrance. I use it morning and evening, and in the evening it goes on after my retinal, before the cream. £16.14.
Daily sunscreen
Purito Wonder Releaf Centella Daily Sun Lotion SPF50+Light, no white cast, dewy finish. The step I'd never skip with a retinal. £13.60.
What I'd buy first
You don't need all of this. If I were starting from nothing, this is the order I'd go in:
- A sunscreen you will wear daily.
- A moisturiser that keeps your skin comfortable.
- The retinal.
- A calming serum, only if your skin asks for it.
Sunscreen and moisturiser come before the retinal because they are what make a retinal easier to live with. Don't add anything else in the same week, so that if your skin reacts, you know why.
How do you step up without undoing the progress?
A higher strength is a new product, so treat it like one.
- Follow the new product's directions. Celimax's own directions say that if you are new to retinol or retinal, use it in the evening every other night for the first two weeks, use a small amount, and wear sunscreen the morning after. Check the box for the current wording.
- Don't carry over your old frequency. If your skin feels a little dry or tight, use less product and use it less often, with a moisturiser containing soothing ingredients.
- Know dry from irritated. If your skin keeps stinging, burns, or looks red or inflamed, cutting back is not enough. Pause the retinal and let your skin settle before you try again.
- Patch test first. Celimax recommends it.
- Stop and ask for advice if you get burning, a rash or swelling, or if irritation doesn't settle. Persistent or worsening symptoms go to a pharmacist or GP.
Not sure where you fit?
Send me what you use now, how often, and what your skin does. I reply personally with what I'd keep, what may be unnecessary, and whether a change is worth considering. You don't have to buy anything.
Send me your routineSkin Advice is a cosmetic routine review. It is not a diagnosis, and it never changes anything prescribed to you.
Mari, K Skin Aura, London
About Mari. Mari is the founder of K Skin Aura, a UK Korean skincare retailer. She has been obsessed with skincare since her teens and experimented heavily, which damaged her skin barrier. She rebuilt it by learning to read ingredient lists and studying Korean skincare, which she loves. After a trip to South Korea she started selling Korean skincare in April 2025. She reviews cosmetic routines and product choices through K Skin Aura's free Skin Advice service. She is not a dermatologist or clinician.
Sources checked. Celimax official page for the Retinal Booster (celimax.us): directions, patch test · Celimax ingredient list and 0.1% retinal figure, as supplied by K Skin Aura for this product · DermNet NZ: topical retinoids · Purito product pages and K Skin Aura product records · Aestura AtoBarrier365 Cream, K Skin Aura product record · K Skin Aura: how to use azelaic acid in a skincare routine
Frequently asked questions
Is 0.1% retinal too strong for a beginner?
It depends on the person and the formula. Celimax gives a gentle introduction for newcomers, but 0.1% is 40 times 25 ppm in stated concentration, so I'd treat it as a bigger step than the label may suggest.
What is ppm?
Parts per million. 10,000 ppm is 1%.
Can I use the 25 ppm and the 0.1% together?
I wouldn't. One retinal at a time, in the evening.
Do I need a special moisturiser with a retinal?
No. Any moisturiser your skin tolerates will do. I suggest a barrier cream because it is built for comfort, not because a retinal requires it.
Can I use azelaic acid and retinal in the same routine?
Some people do, but both can irritate, so I wouldn't start them together. Add one at a time, and let your skin settle on the first before you bring in the second. When you do, keep them on different nights rather than layering them. If your skin stings, burns or looks inflamed, pause the newer one. Our guide to using azelaic acid in a skincare routine explains where azelaic acid fits and how to introduce it gradually. The directions on each pack, and how your own skin responds, come first.
How do I know when to stop and not just adjust?
Mild dryness or tightness: use less, less often. Persistent stinging, burning, a rash, swelling or inflamed skin: pause it and ask for advice.
Does a higher strength work faster?
I can't promise that, and I wouldn't choose a product on that basis.
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