Obagi Vitamin C: 10%, 15%, or 20%? Choosing Your Professional-C Strength

Why Obagi Professional-C?

Most vitamin C serums use a derivative of the vitamin. Obagi's Professional-C range doesn't – it uses L-ascorbic acid, the pure form, and the one that's been studied more than any other. That matters because derivatives have to be converted by your skin before they do anything, while L-ascorbic acid skips that step, so the antioxidant benefit is there from the moment it goes on.

The range comes in three strengths, same core ingredient, different concentration. Which one suits you depends less on budget and more on your skin and how much vitamin C it's used to.

Professional-C Serum 10%

The one to reach for if you've never used a vitamin C serum, or if your skin tends to flare at the first sign of an active. Ten percent is a gentle introduction – it still gives daily antioxidant support and a brighter, fresher look over time, but it's mild enough that reactive skin can usually settle into it without fuss.

Professional-C Serum 15%

The middle strength, and the one most people end up loving. It suits normal, oily, dry and combination skin, and it's a sensible pick if you're bothered by uneven tone or patches of discolouration. Used correctly: cleanse and tone, apply five to seven drops in the morning, let it settle, moisturise, then finish with SPF before any make-up. Use it up within three to six months of opening.

Professional-C Serum 20%

The strongest in the line, and the range's bestseller. Twenty percent is a lot of active vitamin C, so it's really meant for people who've built up to it – if you've got stubborn dark spots or want the most visible brightening the range can offer, this is it. Not a first serum, though; start here and you're more likely to get tingling and redness than results.

FX C-Clarifying Serum

A bit different from the three above. This pairs vitamin C with arbutin, aimed squarely at uneven tone and the appearance of hyperpigmentation. If that's your main concern rather than general brightness, it's worth a look.

A word on L-ascorbic acid

So why does Obagi bother with the pure form when it's harder to work with? Because it's the most researched vitamin C there is, your skin absorbs it directly, and it works well alongside vitamin E for a stronger antioxidant effect. The catch is stability: L-ascorbic acid doesn't like light or air. Left exposed, it oxidises – you'll spot it happening as the serum shifts towards orange or brown, works less well, and can start to sting skin that was fine with it before. Keep the bottle somewhere cool and dark, screw the lid on properly, and don't hang on to it for a year.

Which strength is yours?

• Reach for 10% if you've never used vitamin C, your skin is sensitive, or other vitamin C products have caused problems
• Go for 15% if you've used vitamin C before without drama, want visible brightening, and your skin sits in the normal to combination range
• Step up to 20% if you're an old hand with vitamin C, have stubborn dark spots, and want the most the range can give

Small things that make a difference

Apply it to dry skin – water sitting on the surface can knock vitamin C off before it's done anything, so pat dry first. Give it a minute or two before the next product goes on, store it properly, and use it daily, since consistency does far more than any single application. Keep the SPF going too, as vitamin C and sunscreen make a genuinely good team. If your skin protests with tingling or redness that lingers, drop back to every other day, build up more slowly, or step down to a lower strength.

Where most people land

There's a Professional-C for pretty much everyone. Start cautious, watch how your skin takes it, and move up only when it's ready. For the majority, 15% is the comfortable sweet spot. Browse the full Obagi range, compare strengths against other brands in our guide to the best vitamin C serums in the UK, or explore options for uneven tone in our guide to hyperpigmentation products.

Frequently asked questions

What percentage of vitamin C should a beginner use?

Obagi Professional-C Serum 10% is the recommended starting point for anyone new to vitamin C or with sensitive skin.

Why does Obagi use L-ascorbic acid instead of a vitamin C derivative?

L-ascorbic acid is the pure, most-researched form of vitamin C. Unlike derivatives, it doesn't need to be converted by the skin first, so its antioxidant benefit is available immediately.

How do I know if my vitamin C serum has oxidised?

Oxidised L-ascorbic acid turns orange or brown and loses potency. Store the serum somewhere cool and dark, keep the lid tightly closed, and use it within three to six months of opening.

Can I use Professional-C Serum 20% straight away?

It isn't recommended. The 20% strength is best reserved for people who've already built tolerance on 10% or 15%, since starting at the highest concentration increases the chance of tingling and redness.