What Serum Should I Use? A Clinician's Guide to Treatment Serums
Serum School: everything you actually wanted to know about serums
Retinol. Retinal. Niacinamide. Vitamin C. AHA. BHA. Ten per cent of this, one per cent of that.
If choosing a serum has ever made you close the tab and just buy whatever was trending, you're not alone. It's the question I was asked most in clinic, and the one most brands make harder than it needs to be.
Here's the truth: serums are the most powerful step in your routine. They're where the real work happens. But only if you choose the right one for your skin, and use it the right way.
So welcome to Serum School. In this guide I'll explain what a treatment serum actually does, help you find the one your skin needs, tell you exactly what's in ours and why, and show you how to use them without overdoing it.
Gabrielle Singh, Cosmetic Dermal Clinician and founder of iyvos
Before class: what does a serum actually do?
A treatment serum is a lightweight formula with a high concentration of active ingredients, designed to target a specific concern: fine lines, pigmentation, breakouts, redness or dullness.
Think of your routine like this:
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Your cleanser clears the way.
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Your serum does the targeted work.
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Your moisturiser hydrates and protects your barrier.
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Your SPF protects the results.
The most common mistake I see is people assuming their moisturiser is doing the same job as a serum. It isn't. A moisturiser is designed to sit on the skin and hold hydration in. A serum is designed to deliver actives where they can make a visible difference. You need both, and they're not interchangeable.
That's why a serum is usually the most expensive product in a routine. It's also the one that changes your skin the most.
Find your serum by skin concern
Start with the one thing you'd most like to change about your skin right now. That's your first serum.
Still not sure? Take our skin assessment and we'll point you in the right direction.
Lesson 1: Retinal vs retinol, and why we chose 1% pure retinal
This is the serum I'm proudest of, so let me explain what makes it different.
What's the difference?
Vitamin A is the most researched ingredient in skincare for smoothing fine lines, refining texture and helping skin renew itself. But your skin can only use it in one form: retinoic acid. Everything else has to be converted first.
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Retinol takes two conversion steps to become retinoic acid.
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Retinal (retinaldehyde) takes just one.
Fewer steps means more of what you apply actually goes to work, and you tend to see results sooner. That's why I chose retinal.
Why 1% matters
Most retinal serums sit somewhere around 0.05% to 0.2%. Active A contains 1% pure retinal. That's a genuinely high-strength formula, made for people who want real, visible change in fine lines, texture and tone.
Strength on its own isn't the point, though. We paired it with 4% niacinamide to help support your skin barrier while the retinal does its work, and peptides to help skin look firmer and smoother.
Who it's for
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You're noticing fine lines or a loss of firmness
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Your texture feels rough or uneven
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You get congestion alongside the first signs of ageing
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You've used retinol before and want to step up
How to use it: at night, after cleansing and before moisturiser. Start two to three nights a week and build up as your skin adjusts. Use SPF every morning. If you're pregnant or breastfeeding, don't use vitamin A.
Lesson 2: Does stronger mean better?
Not on its own.
The strongest serum in the world won't help if your skin can't tolerate it. Push too hard, too fast, and you end up red, flaky and sensitised, and most people stop altogether. I saw it constantly in clinic.
Potency works when it's matched with the right frequency and enough barrier support. That's why Active A is 1% retinal and 4% niacinamide, and why we tell you to start slowly.
How to start a strong active
If your skin feels irritated, drop back a step. Slower is still progress. And always pair actives with a good moisturiser and daily SPF.
Lesson 3: What 10% niacinamide actually does
If Active A is the hardest worker in the range, Active B is the one that gets along with everyone.
Niacinamide (vitamin B3) is one of the most versatile ingredients in skincare. At 10%, it helps calm redness, support your skin barrier, refine the look of enlarged pores and even out skin tone. We've paired it with panthenol (vitamin B5) and glycerin to keep skin hydrated and comfortable, plus hyaluronic acid for a plumper feel.
It's for you if: your skin is red, reactive, breakout-prone or dehydrated, or you want a serum you can use alongside anything else.
How to use it: morning and night, after cleansing and before moisturiser.
Lesson 4: Vitamin C without the sting, and Kakadu plum
If vitamin C has ever made your skin sting or tingle, you've probably used the pure form, L-ascorbic acid. It's effective, but it's unstable and can be harsh on sensitive skin.
Active C uses ascorbyl tetraisopalmitate, a stable, oil-soluble form of vitamin C that's much gentler on the skin. Alongside it is Kakadu plum, a native Australian fruit and one of the richest natural sources of vitamin C in the world. Together with gentle AHAs, they help brighten dull skin, even out tone and reduce the look of pigmentation.
It's for you if: your skin looks dull, tired or uneven, or you're working on pigmentation.
How to use it: every morning, after cleansing and before moisturiser and SPF.
Lesson 5: AHA vs BHA, what exfoliating serums do
Dull, bumpy or congested skin is often just skin holding onto cells it should have let go of. That's where chemical exfoliants come in.
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AHA works on the surface, gently loosening dull cells to smooth texture and bring back glow.
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BHA is oil-soluble, so it works inside the pore to help clear congestion and blackheads.
Together, they make our Resurfacing Serum the easiest entry point into actives, and at $65 it's the most accessible serum in the range.
It's for you if: you have rough texture, congestion, blackheads or skin that looks flat.
How to use it: at night, two to three times a week, after cleansing and before moisturiser. Use SPF every morning.
Lesson 6: Which serums can you use together?
This is where most people go wrong, so here's the simple version.
Active A, Active C and Resurfacing Serum all encourage your skin to renew itself. Layering them on top of each other is the fastest way to irritate skin. Active B is the opposite: it calms and supports, so it pairs with everything.
Our serum duos
To take the guesswork out, we've put together two pairings:
First Class: Active B + Resurfacing Serum. The easy introduction to actives. Resurfacing smooths and clears, while Active B keeps skin calm. Perfect for congestion, dullness and anyone new to serums. [Shop First Class]
Advanced Class: Active A + Active B. For when you're ready for 1% retinal. Active A does the heavy lifting on fine lines and texture, and Active B supports your barrier the whole way. [Shop Advanced Class]
Lesson 7: Your Serum School report card
Everything above on one page. Save this one.
The three rules
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One renewing serum per night: Active A or Resurfacing, never both.
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Vitamin C in the morning, retinal at night.
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Active B goes with everything, so use it whenever your skin wants extra calm.
You don't need all four serums to follow this. Pick the treatment serum for your main concern, add Active B if you'd like, and leave the other steps as they are.
Extra credit: "My serum isn't working…"
If you're two weeks in and wondering whether you've wasted your money, you probably haven't. Your skin renews its surface roughly every four weeks, and that slows as we age, so most serums need four to twelve weeks of consistent use to show real change.
You'll often feel a difference first, skin that's softer, calmer or more hydrated. The visible changes in tone, texture and fine lines come later.
Before you give up on a serum, check these four things:
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Are you using it consistently? Two or three times a week when you remember isn't the same as a routine.
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Are you using enough? Two to three drops for your whole face is about right.
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Is it in the right place? Serum goes on clean skin, before moisturiser. On top of a heavy cream, it can't do its job.
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Are you wearing SPF? Without it, the sun undoes the work your serum is doing, especially for pigmentation.
If all four are right and you've given it twelve weeks, it may be the wrong serum for your concern, and that's when to rethink, not before. For more on building the full routine around your serum, read our guide to how to build a skincare routine.
Serum FAQs
Is retinal better than retinol?
Retinal converts to retinoic acid, the form your skin uses, in one step, while retinol takes two. That generally means retinal works faster. It can also be more active on the skin, which is why starting slowly matters.
Can I use retinal and vitamin C together?
Yes, but not at the same time. Use vitamin C in the morning and retinal at night. Our Active C contains AHAs, so keep it away from your retinal nights.
Can I use niacinamide with retinal?
Yes. They're a great pairing, and our Active A already contains 4% niacinamide. Adding Active B on top gives your barrier even more support.
Should I use a serum in the morning or at night?
It depends on the serum. Vitamin C belongs in the morning, under SPF. Retinal and exfoliating serums belong at night. Niacinamide works at either time.
How many serums should I use?
One or two is plenty for most people. Choose one for your main concern, and add Active B if you want extra calm and barrier support.
What's the difference between a serum and a moisturiser?
A serum delivers concentrated actives to target a concern. A moisturiser hydrates and protects your skin barrier. Use your serum first, then moisturiser on top.
Class dismissed
You don't need every serum. You need the right one, used the right way, for long enough to see what it can do.
Find the concern that matters most to you, start with that serum, and give it twelve weeks. I'd love to hear how your skin is feeling at the end of it.
Not sure where to start? Take our skin assessment, or send us a DM on Instagram @iyvosskin and our team will help you choose.
