Vitamin C is a must-have skincare ingredient, but how do you find one that packs a punch yet won’t sting or irritate? We’ll tell you exactly

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Ask any skincare experts for their non-negotiables and they’ll mention SPF, retinoids – and vitamin C. Acting as a potent antioxidant, skin-brightener, pigmentation-fader and collagen-booster, it’s one of skin’s best allies, coming especially into its own in summer. According to Paula Begoun, founder of Paula's Choice, vitamin C’s antioxidant powers are “particularly effective at fighting off damage from UV rays, so increasing the effectiveness of your sunscreen with an added level of protection.” Combined with vitamin E, the sun protection is even greater, studies say (though this is not your cue to skip or lower your SPF).

Unlike with retinol, which can irritate skin at minute percentages of 0.2%, vitamin C is much less likely to have adverse side effects - you want a 10% dose of it to get maximum benefits from this multi-tasker. Having said that, as a skincare ingredient, vitamin C comes in multiple forms, some of which bite a lot harder than others. So to find one that’s gentle enough for your skin type but packs enough power to make a visible difference to your complexion, you need to focus not just on a punchy percentage, but on the type of vitamin C in the formula as well. Below are the facts you need to know, and the C-powered serums we most rate.

The pure and most potent C: l-ascorbic acid

  • Acidic, so can sting
  • Water-soluble so often in very light serums
  • Goes off quickly so you need to use it up fast
  • Can come as vitamin C powder alongside a serum, which you mix yourself
  • Experts advise 10-15 per cent for wrinkle and brown spot reduction
  • Studies show no real additional benefits over 20 per cent
  • Also comes as ‘3-O ethyl ascorbic acid’, which is more stable and won’t sting

The active molecule in any vitamin C that does all the work (in the same way that retinoic acid is the active molecule in all retinoids) is l-ascorbic acid. 10% or more of this ingredient in its pure form will go beyond defending your skin from pollution and UV and actively work on fading pigment and lines.

But there are two issues. Number one, it’s the acidic form of vitamin C and for it to work, it needs to come in an acidic base – and that’s why pure l-ascorbic acid serums can sting. This is often temporary, but if skin is quite sensitive, irritation can ensue.

Two: the molecule is desperately unstable, and when mixed with water, it will oxidise (go off) in a matter of weeks or even days. Because most skincare is up to 85% water, this is a problem, but there are solutions. One is to deliver the vitamin C as a powder that can be mixed with a liquid base right before use, so the product is applied fresh. Another trick is to formulate the ascorbic acid with powerful antioxidants, which will delay the oxidation process. In either case, a change in colour is a sure sign of oxidation, so if your clear serum is turning a pale orange and subsequently a brown-ey orange, you know it’s gone off and it’s best not to use it any longer.

A third trick is to put the l-ascorbic acid, through a process that stabilises it without it losing any of its potency – it’s called ‘ethylation’. So 3-O ethyl ascorbic acid is as powerful as l-ascorbic acid, but won’t sting on application. Fab, although it can irritate at high percentages if you’re sensitive.

Both forms of ascorbic acid are good antioxidants at 5 per cent, but 10-15 per cent is seen as the sweet spot for brightening and line-fading. Over 20 per cent, the chances of irritation are high and “research suggests there is no additional benefit,” says cosmetic physician Dr Sophie Shotter. That doesn’t stop brands from offering up to 30 per cent, and some customers loving it.

As found in: Clinique Fresh-Pressed Daily Booster, see below

The gentle-giant C: THD ascorbate

  • Also labelled as tetrahexyldecyl ascorbate, or ascorbyl tetraisopalmitate
  • Stable, so better shelf-life
  • Oil-soluble so found in face serums, oils and creams
  • Easily absorbed, so lower percentages get good results

This oil-soluble vitamin C derivate is flavour of the month (or rather, the past few years) among vit C buffs. Found on your INCI list as THD ascorbate, tetrahexyldecyl ascorbate, or ascorbyl tetraisopalmitate (yep, all the same thing….), it has to convert into active l-ascorbic acid once it’s absorbed, so the percentage of the active molecule inside the skin ends up being a lot lower than the percentage of vitamin C advertised on the bottle.

But on the big plus side, THD ascorbate has been shown to be the most bio-available form of vitamin C, meaning it’s most likely to penetrate the collagen-generating dermal layer. And it does it without any irritation at all.

That means you can go to town in terms of percentages. Any THD ascorbate is a good thing, but the more the merrier, really.

As found in: The Ordinary Ascorbyl Tetraisopalmitate Solution, see below

The slow-but-stable Cs: the ‘ascorbyl’ family

  • Ascorbyl glucoside, magnesium ascorbyl phosphate, sodium ascorbyl phosphate and ascorbyl palmitate
  •  Most are water-soluble (but ascorbyl palmitate is oil-soluble). You’ll find them in both serums and creams.
  • Stable, so better shelf-life
  • Non-irritating
  • Look for high percentage (20 per cent and upwards) to be effective
  • Look for potency-boosting ingredients like niacinamide

The above are just some of the many other vitamin C derivatives or compounds doing the rounds, all created in an effort to turn the volatile l-ascorbic acid into a stable and long-lasting skincare ingredient. And stable they all are, as well as non-irritating. The problem is, they all need to convert upon application and therefore only leave a small amount of l-ascorbic acid in the skin. In not-rare cases, this means that your ‘10% vitamin C serum’ delivers as little as 0.2% active vitamin C. Disappointing!

Among this lot (note all forms of vitamin C have the word ‘ascorb’ in it), ascorbyl glucoside is worth a try if combined with niacinamide, which boosts its potency.

If any of these are the vitamin C in your serum, you want a big percentage of it (say 20% or more) to get the C-benefits.

As found in: Nip + Fab Vitamin C Fix Concentrate Extreme, see below

Beware the packaging

It’s a game of tongue-twisters, but knowing them makes all the difference. Just one more word of advice: make sure your serum comes in an opaque or dark bottle so it’s not exposed to oxidising sunlight, and don’t buy and orange l-ascorbic acid-based product: that way you won’t be able to see if it’s changing colour and going off. It’s the little things!

Below are where you’ll find all the Cs in powerful percentages.

The best high-strength vitamin C serums for your skin type

 Best brightening high-strength vitamin C: Nip + Fab Vitamin C Fix Concentrate Extreme 15%, £24.95

Lightweight and non-oily, its 15% is a complex of no less than three different types of vitamin C including the extra-potent ethyl ascorbic acid, plus it has ferulic acid and niacinamide to boost the powers of the other Cs, and soothing agents should your skin shy away from all that might. Your skin will look brighter in weeks.

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Best high-strength vitamin C for sensitive skin: Revision Skincare C-Correcting Complex, £187.40

This is a light lotion texture packed to the rafters with THD ascorbate vitamin C, lauded for its deep-penetrating delivery. Teamed with vitamin E, prebiotics and a host of other skin repair agents, its costs a lot but works damn hard for the money without a chance of irritation.

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Best plant-powered high-strength Vitamin C: Farmacy Beauty 10% Waterless Vitamin C Serum, £48 

This serum pulls the very neat trick of feeling slippery-watery, but having no water in it at all. That means the pure l-ascorbic acid in it won’t go off, and you’ll get the full hit of 10% vitamin C until your bottle is empty. Ferulic acid, arbutin, lactic acid and a host of citrus peel extracts collaborate to work on dullness and hyperpigmentation, too.

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Best freshly-mixed high-strength Vitamin C: Clinique Fresh-Pressed Daily Booster with Pure Vitamin C, £63

Press the top of each vial to release fresh l-ascorbic acid powder into a weightless, antioxidant-spiked watery base to create a C serum at the height of its active power. Each vial lasts a week so you’ll have used it up before it has a chance to oxidise. Wash your hands after use – fresh vitamin C will stain your hands like bad fake tan!

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Best budget high-strength vitamin C: The Ordinary Ascorbyl Tetraisopalmitate Solution 20% in Vitamin F, £17.60

A potent 20% of the oil-soluble, collagen-boosting vitamin C derivative ascorbyl tetraisopalmitate (also known as THD ascorbate), this light, unscented and fatty acid-rich oil feels like a face oil – but one with serious skin-smoothing benefits and a small price tag.

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Best high-strength vitamin C for oily skin: SkinCeuticals Silymarin CF, £165

SkinCeuticals launched Silymarin CF in December 2020 as a non-identical, non-oily twin to the famous CE Ferulic, specifically for oily, breakout-prone skin. The price is eye-watering, but it has 15 per cent l-ascorbic acid vitamin C, alongside 0.5 per cent ferulic acid for stability and  glow-boosting. Plus  there's 0.5 per cent silymarin which ups the antioxidant protection and helps limit breakouts and 0.5 per cent salicylic acid  to gently unclog pores.

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Best high-strength vitamin C for fading brown spots: Perricone MD Vitamin C Ester CCC+ and Ferulic Brightening Complex 20%, £133 

There are three powerful types of vitamin C (hence CCC) in this 20 per cent serum, as well and power players vitamin E and ferulic acid. All of them, alongside exfoliating glycolic acid, make for a skin-resurfacing potion with oomph. Perricone's most potent C,  it is nonetheless silky-textured and non-stinging. Just don't use this in the sun because of the glycolic acid, and approach with caution if your skin is sensitive.

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Best high-strength vitamin C for firmer skin: Allies of Skin 20% Vitamin C Brighten + Firm Serum, £85 

This serum has an unusual honey-like texture that feels nourishing on dried-out skin while at the same time giving a boost of antioxidants. It has a whopping 20% of the full-on potent, full-on stable ethyl ascorbic acid, plus orange extract to boost elasticity and super-antioxidant glutathione to protect skin and diminish dullness. 

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Best high-strength vitamin C for improving skin texture: Paula's Choice C15 Super Booster, £52

Part of Paula's Choice's boosters range, these water-based drops you add to your moisturiser or serum. They combine 15 per cent l-ascorbic acid with vitamin E and ferulic acid as well as skin-smoothing peptides to improve skin texture. Add two to three drops to your skincare routine and watch your glow emerge.

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Best high-strength vitamin C for glow:  Ole Henriksen Banana Bright Vitamin C Serum, £46.40

Founder of brow brand Refy  Jess Hunt says she can't go without this zesty-smelling gel-cream serum, which gives her a glow so bright she's convinced it can be seen through makeup! It feels ultra-smooth on the skin (no stickiness here) and gives a real freshness to the face. It has 15 per cent l-ascorbic acid vitamin C along with five per cent gentle  PHAs  to whisk away dead skin cells for an even brighter complexion. Hyaluronic acid adds dewy hydration.

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Best high-strength vitamin C for nighttime rejuvenation: DCL C Scape High Potency Night Booster 30, £108 

Unlike many vitamin Cs, this one has to be applied at night. A water-free cream texture with 30 per cent l-ascorbic acid and THD ascorbate, it's seriously strong and stable, but it does sting. Trinny Woodall says that after using it at bedtime she always wakes up with a bright glow and we believe her. It supports collagen production and promotes an even skin tone.

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Best high-strength vitamin C for an even skin tone: Medik8 Super C Ferulic, £59 

This is Medik8's most powerful vitamin C, fusing 30 per cent 3-O ethyl ascorbic acid, , antioxidant ferulic acid, vitamin E and brightening, glow-giving turmeric  which blocks the tyrosinase enzyme that produces melanin. Together, they will go a long way to even out your skin tone. For such a high-strength vitamin C, this is a reasonable price, as we've come to expect from Medik8. It has a slippy-feeling yet oil-free texture that absorbs quickly so you can get on with the rest of your routine.

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Best high-strength vitamin C for acne-scarring: Beauty Pie Superdose CC-Suite Rapid Action Power Brightener, £100 (members £16.50)

This non-greasy vitamin C serum sandwiches 15 per cent sodium ascorbyl phosphate vitamin C (stable, but it does need to convert so you don't get 15% pure vitamin C) with ferulic acid and tranexamic acid to brighten dull and uneven including, says the brand, scars. The tranexamic acid helps reduce the appearance of hyperpigmentation that often comes with scars. It does have that unmistakable meaty smell vitamin C has (yes meaty, not orangey) but when it has an effect on acne scarring we can put up with that.

Not a member of Beauty Pie? Join using code GTGSENTME and get an extra £50 to spend.

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Best high-strength vitamin C for a fresh complexion: Drunk Elephant C-Firma Day Serum, £70 

Now that Drunk Elephant has landed at Boots, there are Advantage points to be had in stocking up on one of our favourite brands, including this watery-fresh 15 per cent l-ascorbic vitamin C serum. It also has one per cent vitamin E and 0.5 per cent ferulic acid to help keep the ascorbic acid from deteriorating (you're  advised to keep the serum in the fridge for the same reason) . Pumpkin and pomegranate extracts work away at dead skin cells for extra brightening.

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Ingeborg van Lotringen is author of  Great Skin: Secrets the Beauty Industry Doesn't Tell You.