Its as easy as CSA

In 2009, Medik8 introduced the CSA Philosophy — a remarkably straightforward approach, grounded in scientific principles, that delivers undeniable results. The method has been gaining widespread acceptance ever since, and Medik8 couldn't be more thrilled about it. Simply use a vitamin C serum plus sunscreen during the day, and vitamin A at night. That really is all it takes.

By nurturing your skin and following that uncomplicated advice, Medik8 believe you can keep your complexion looking its best well into your fifties and beyond. It isn't marketing shorthand either — it's built on decades of dermatological research into what genuinely makes a visible difference to skin over the long term.

What CSA Actually Stands For

Three letters, three jobs:

C — Vitamin C, every morning. Antioxidant defence against the daily environmental exposure that drives visible ageing.
S — Sunscreen, every morning. The single most effective thing you can do to protect how your skin looks over time.
A — Vitamin A, every evening. The ingredient with the deepest body of evidence behind it for smoother-looking, more even skin.

Two products in the morning, one at night. Everything else — cleansers, moisturisers, eye products, masks — sits around that core rather than replacing it. That's the whole point: a routine you'll actually keep up beats an elaborate one you abandon by February.

C Is for Vitamin C

A well-formulated and stabilised vitamin C serum does more than one job at once. It offers vital antioxidant protection against free radicals, helps keep skin tone looking clearer and more even, and is the ingredient most associated with smoother, more radiant, firmer-looking skin over time. It also works beautifully alongside sunscreen — the two complement each other, which is exactly why CSA pairs them.

Apply vitamin C in the morning, to clean skin, before your sunscreen. That way it's in place to shield your skin from the daily environmental factors that contribute to visible ageing. If you want the full picture of how it behaves once it's on the skin, our guide to what a vitamin C serum is actually doing to your skin goes into proper detail.

Medik8's Vitamin C Ladder

Medik8's C-Tetra range is built in progressive strengths, so you can start gently and work upwards as your skin gets comfortable:

C-Tetra (7%) — the entry point, and a sensible first vitamin C for most people.
C-Tetra Luxe (14%) — a richer texture with a step up in strength, for enhanced radiance.
C-Tetra Advanced (20%) — the highest strength in the C-Tetra range, for skin already used to a daily vitamin C.

Sitting alongside the ladder rather than on top of it is Super C Ferulic, which uses 30% ethylated ascorbic acid — a different form of vitamin C rather than a stronger version of the same one. Medik8 treat it and C-Tetra Advanced as an either/or choice rather than consecutive steps: Super C Ferulic suits skin showing more advanced sun-related pigmentation and is not intended for sensitive skin, while C-Tetra Advanced is the gentler-textured option.

There's no prize for starting at the top. A lower-strength vitamin C used every single morning will do far more for your skin than a high-strength one that stings and ends up at the back of a drawer. If you'd like to compare across brands before committing, our roundup of the best vitamin C serums in the UK is a good place to look.

S Is for Sunscreen

The majority of visible skin ageing is attributed to sun exposure. And sun damage doesn't only happen on bright summer days — if there's daylight, the sun's rays are still reaching your skin. Cloud reduces UV, but it does not remove it — UVA in particular passes through cloud far more readily than UVB, which is why exposure continues on overcast days. To keep a youthful-looking complexion, high-strength sun protection needs to be a daily habit, not a holiday one.

A broad-spectrum sunscreen worn every day helps prevent UV damage and the dark spots that follow it. It's the most protective step in the entire routine, and the one people most often skip between October and March.

At Medik8, they offer a range of light and powerful sunscreens that protect and nourish the skin at the same time. Rest assured, Medik8's advanced sunscreens won't leave you feeling sticky and greasy the way beach formulas can. In fact, you may not even realise that your luxurious day cream contains sunscreen at all. Options across the range include:

Advanced Day Ultimate Protect SPF 50+ — the highest protection in the range, with antioxidants built in.
Advanced Day Total Protect SPF 30 — a lighter daily moisturiser-and-SPF in one.
Daily Radiance Vitamin C SPF 30 — combines the C and the S of CSA in a single morning step.

That last one is worth flagging if mornings are rushed: a combined vitamin C and SPF collapses two steps into one without losing either. For a wider comparison of daily facial SPFs, see our guide to the best broad-spectrum facial sunscreens in the UK.

A Is for Vitamin A

As leading experts in vitamin A (also known as retinol), Medik8 have developed an extensive collection of night creams and serums designed to work on the look of your skin while you sleep. Vitamin A is arguably the most important ingredient in anti-ageing skincare: it encourages a fresher, smoother-looking surface, helps soften the appearance of fine lines and uneven tone, and tends to leave skin feeling less oily over time.

It matters that the vitamin A is stabilised and uses a controlled-release mechanism. That's what allows a formula to stay potent while minimising the irritation that puts so many people off retinoids in their first fortnight.

Medik8's Crystal Retinal range is formulated with retinaldehyde — a form of vitamin A that sits one conversion step closer to the skin's active form than retinol does, which is why it is often favoured by people who want results without stepping up to a prescription retinoid. Medik8 puts the conversion advantage at around 11 times faster than retinol, meaning skin can start putting the active to work sooner.

Choosing Your Crystal Retinal Strength

The range is numbered so you can climb it gradually:

Crystal Retinal 1 (0.01%) — for very sensitive skin, or a very cautious start.
Crystal Retinal 3 (0.03%) — the usual beginner's step for anyone new to vitamin A.
Crystal Retinal 6 (0.06%) — for skin with some vitamin A experience behind it.
Crystal Retinal 10 (0.1%) — for regular retinoid users.
Crystal Retinal 20 (0.2%) — for experienced users on a well-established routine.
Crystal Retinal 24 (0.24%) — the maximum strength in the range.

Start low, use it two or three nights a week, and only move up a level once your current one is completely comfortable. There is no benefit whatsoever in rushing the ladder. Our guide to retinol and its powerful cousins explains how the different forms of vitamin A compare, and the best retinol serums in the UK covers the wider retinoid category.

Building Your CSA Routine

Here's how the philosophy translates into an actual morning and evening, using Medik8's own line-up as the example:

Morning

Cleanse — something gentle, such as Surface Radiance Cleanse.
Vitamin C serum — your chosen strength from the C-Tetra range.
Sunscreen — either a dedicated SPF or a moisturiser with broad-spectrum protection built in.

Evening

First cleanse — an oil or balm such as Lipid-Balance Cleansing Oil, to lift off sunscreen and makeup.
Second cleanse — a gel or foam cleanser on bare skin.
Crystal Retinal — your chosen strength, on dry skin.
Night moisturiser — something comforting such as Advanced Night Restore.

That's it. Everything else is optional. If you'd like to add eye products, exfoliating acids or targeted serums later, our ingredient layering guide explains what plays well together and in what order, and our skincare routine fundamentals covers the underlying principles.

Ready-Made CSA Kits

If you'd rather not assemble the three steps yourself, Medik8 have done it for you. Their pre-assembled CSA kits are curated by Medik8's own team and presented in their own gift box, containing everything you need to get started.

The formulas in each kit have been chosen because they're compatible with one another and among the most popular in Medik8's vitamin C, sunscreen and vitamin A lines — so you get a coherent routine at home whatever your level of expertise or however sensitive your skin. You can also browse the full Medik8 range or the brand's best sellers if you'd prefer to pick your own combination.

Why the CSA Philosophy Works

Strip it back and the logic is simple:

It protects during the day, with antioxidants and sunscreen doing complementary jobs.
It works on the look of your skin at night, when vitamin A has time to do its thing undisturbed.
It uses ingredients that are clinically tested and have decades of evidence behind them, rather than whatever is trending.
It's genuinely simple to follow — just remember CSA.

Anti-ageing skincare doesn't have to be complicated. In fact, it shouldn't be. By following the CSA philosophy consistently, you can improve your skin's tone and texture and keep it looking healthy and youthful — without a ten-step routine or a bathroom cabinet full of half-used bottles.

Frequently Asked Questions

Can I use vitamin C and vitamin A together?

You can — but CSA deliberately separates them, and that's the easier approach. Vitamin C in the morning is where it does the most good, since it partners with sunscreen against daytime exposure. Vitamin A at night avoids any sun sensitivity and gives it uninterrupted hours to work. Splitting them also means less chance of irritation than layering both at once.

Which vitamin A strength should I start with?

If you've never used a retinoid, start at Crystal Retinal 1 or 3, two nights a week, and build up from there. If you've been using a retinol comfortably for a while, 6 or 10 is a reasonable place to begin. Moving up a level is something you earn over months, not weeks.

Do I really need sunscreen every day, even in winter?

Yes. The UV that drives visible ageing is present year-round, and winter sun sits low and reflects — this is the step people most often drop between October and March, and it's the one protecting the results the other two steps are working towards.

What if my skin is sensitive?

CSA still applies — you just move more slowly. Choose the lowest vitamin C strength, a mineral-leaning or fragrance-free sunscreen, and the gentlest vitamin A, and introduce them one at a time with a fortnight between each. Buffering your vitamin A by applying it over a moisturiser is a well-established way to make the first weeks easier.

Is CSA enough on its own?

For most people, yes — it's the foundation, and the foundation is where the results come from. Targeted extras such as eye products, acids or peptide serums are worth adding once the core three are established and comfortable, not before. Our complete guide to anti-ageing skincare covers what's worth adding and when.

How long before I see a difference?

Radiance and texture are usually the first things people notice, and tone and the appearance of fine lines take considerably longer — this is a routine measured in months rather than weeks. Skin renews on its own timescale, and no routine can hurry that along. Consistency matters far more than strength: the same three steps used every day will always outperform a stronger routine used sporadically.

Do I still need separate sunscreen if my vitamin C serum contains SPF?

If you're using Daily Radiance Vitamin C SPF 30, that single step covers both, provided you apply enough product. Otherwise, always follow a vitamin C serum with a dedicated SPF.

Where to Start

If you'd rather browse than be told, these are the best entry points:

Not sure which strengths are right for you? Take our skincare quiz for personalised recommendations, or book a free virtual consultation and one of our skincare specialists will build a CSA routine around your skin.