Behind the Scenes of Our Vitamin C System Trials

I was getting results with my skincare, but I couldn’t stand looking at my crepey chin anymore!

My number one priority was ‘how to smooth out my chin' - I spent hundreds of hours researching ingredients before settling on Vitamin C as the one I wanted to trial. Then I hit the biggest issue with Vitamin C — stability, and how to use it consistently at a meaningful strength without it degrading before I used it.

The search for the right Vitamin C

Before I continue — the pure form of Vitamin C, L-Ascorbic Acid, is a man-made, nature-identical ingredient. There are many forms and derivatives of Vitamin C, but my research went down two parallel routes: pure Vitamin C powder and a stable form of Vitamin C. It didn’t seem possible to get both stability and strength in one ingredient, until I came across THD (Tetrahexyldecyl Ascorbate).

Why I chose THD Vitamin C

THD Vitamin C is a highly stable, lipid-soluble form of Vitamin C. It provides antioxidant protection, supports collagen production, helps protect existing collagen from breakdown and can improve pigmentation and uneven skin tone.

L-Ascorbic Acid is pure Vitamin C in its active form. It is a powerful antioxidant that supports collagen production and can help brighten the skin, reduce pigmentation and improve skin tone and texture.

Next, I got to work formulating the right vehicle for the THD with the aim of helping it penetrate the skin effectively. But I still had one problem — L-Ascorbic Acid is water-soluble, not oil-soluble, so it couldn’t simply be added to the same formulation.

Why 8% THD

After looking at different carrier oils and emollients, I formulated the first test version around one very important requirement: it had to absorb quickly and leave very little residue. THD is an expensive, high-performance active, so I didn’t want to put it into a heavy carrier that simply sits on the surface of the skin. I wanted a light, fast-spreading delivery system that would help the THD distribute efficiently across the skin and feel comfortable enough to use every day.

I settled on 8% THD because I wanted it at a meaningful concentration — not added at a token level simply so Vitamin C could appear on the ingredient list. THD is commonly formulated across a fairly broad range, and 8% put mine towards the higher end while still allowing me to build the lightweight, fast-absorbing carrier system I wanted. More isn’t automatically better; the concentration still has to work with the formulation and actually be delivered effectively into the skin.

Developing the L-Ascorbic Acid Powder

The L-Ascorbic Acid powder took a lot more trial and error. I started by mixing pure Vitamin C powder with water and then worked my way through a number of different L-Ascorbic Acid powders before settling on the one I use now. I wanted a cosmetic-grade, high-purity powder with an ultrafine particle size — something suitable for use on the skin, but also fine enough to dissolve quickly and evenly when freshly mixed.

Plain water worked for testing, but it was never going to be the finished solution. It was too runny, didn’t spread particularly well and didn’t give me the kind of delivery system I wanted. So I developed a dedicated Activation Booster specifically for the powder — something that would dissolve it quickly, spread well across the skin and make freshly activated L-Ascorbic Acid practical to use.

I started testing these two products and within a few weeks I could see a definite improvement in my skin tone and the general bounciness of my skin.  Within 6 weeks I saw a distinct improvement in the crepey appearance on my chin – the excitement was real!

The Vitamin C System We Tested

By this point I had two separate Vitamin C products: the Advanced THD Vitamin C Serum, containing 8% THD in a lightweight oil-based serum, and the Vitamin C Activation System, made up of pure L-Ascorbic Acid powder and its dedicated Activation Booster.

The THD Serum was used every morning. The freshly activated L-Ascorbic Acid was introduced later in the trial and used 2–3 times a week, mixing 1 slightly rounded scoop of L-Ascorbic Acid powder with 3 pumps of Activation Booster immediately before use. This creates a freshly mixed Vitamin C concentration of approximately 14.3%.

How We Structured Our 8-Week Vitamin C Trial

I decided to put together an 8-week user trial to see whether a diverse selection of people, all using a variety of other skincare products, would get similar results.  Some already used Intrinsic products, while others had never used an Intrinsic product before, and they all came into the trial with their own existing skincare routines.

Most importantly, I didn’t tell them what the product was supposed to do or what results they should be looking for. They were given no information about the expected benefits at all — only the instructions and the rules of the trial. I wanted their feedback to come from what they actually noticed in their own skin, not from what I had told them to expect.

The main rule was simple: do not change anything else in your skincare routine for the full eight weeks. No new retinoids, pigmentation products, exfoliants, moisturisers or other treatments. Whatever they were already using, they needed to keep using consistently, so that Vitamin C remained the main new addition.

For the first six weeks, they used the 8% THD Serum every morning. I deliberately kept the L-Ascorbic Acid out of the trial during this period because I wanted THD to have enough time to show whether it could produce visible results on its own.

Progress photographs were taken at Baseline, Week 2, Week 4, Week 6 and Week 8.  The progress photographs were taken without makeup and are shown unfiltered.

Only after the Week 6 photographs were taken did I introduce the freshly activated L-Ascorbic Acid for the final two weeks, while the testers continued with their daily THD Serum.

That structure meant I could look at the first six weeks as the THD phase, and then see what happened once L-Ascorbic Acid was added.

This was a real-world user trial rather than a controlled clinical study, but keeping everyone’s existing routine unchanged and staging the two forms of Vitamin C gave me a much clearer picture of what people were actually seeing.

Vitamin C Trial Results: Week 2

Early days, and several testers hadn’t noticed any change yet. Others were already mentioning smoother skin, better hydration, brighter-looking skin and a more even tone.

Week 4

By Week 4, the feedback was becoming more consistent, particularly around smoother skin, hydration, brighter skin, more even tone and softer-looking lines. A few testers were still seeing little or no change.

Week 6: THD Results Before L-Ascorbic Acid

This was the important checkpoint: THD only, before the L-Ascorbic Acid was introduced. We were already seeing repeated feedback around smoother, brighter, more even-looking skin and softer-looking fine lines.

Week 8: Adding Fresh L-Ascorbic Acid

After two weeks of adding freshly activated L-Ascorbic Acid, the main themes remained smoother, brighter, more even-looking skin, softer-looking lines and lighter-looking pigmentation or sun spots. Some testers felt the Booster accelerated their results, while others noticed little additional change.

Beyond the Trial: Dale at Week 10

Dale chose to continue using the products beyond the formal 8-week trial, so we continued taking progress photographs through to Week 10. Having already seen Dale’s progress at Week 6, the Week 10 photograph gave us the opportunity to see what happened when use continued beyond the trial period.

What We Took From the Vitamin C Trial

By the end of the eight weeks, some very clear themes had emerged: smoother and brighter-looking skin, more even tone, softer-looking lines, lighter-looking pigmentation or sun spots and generally healthier-looking skin.

One of the things that surprised me most was how many testers had underestimated their own results. When I put their baseline and Week 8 photographs side by side, several were genuinely surprised by the difference. When you look at your own face every day, gradual changes can be very easy to miss.

Not everybody had the same experience. A few testers noticed brief stinging or tightness when they first introduced the freshly activated L-Ascorbic Acid, which generally settled quickly. One breakout-prone tester completed the full eight weeks but decided the products weren’t right for her skin and didn’t continue afterwards.

What I found most satisfying was what happened after the trial ended. Several participants went on to become customers and continued using the products because they liked what they had seen in their own skin.

For me, that was the result I was looking for: not identical results on every face, but clear, recurring changes across very different skin and skincare routines.