I need to talk to you about vitamin C, because there’s a form of it most brands don’t use, and once you understand why, you’ll never look at your skincare the same way.
The problem with traditional vitamin C serums
Most vitamin C products on the market use L-Ascorbic Acid, the classic form. It does deliver results, but it comes with real drawbacks:
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It’s unstable. L-Ascorbic Acid oxidizes quickly when exposed to light or air — that’s why your serum turns orange or yellow. Once it oxidizes, it’s no longer effective and can actually cause irritation.
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It requires a very low pH (around 3.5) to penetrate skin, which makes it too acidic for sensitive or reactive skin types.
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It degrades fast. Even sealed, the shelf life is short, meaning the product you paid for may not be working by the time you’re halfway through it.
Enter THD — the more stable, more skin-friendly alternative Tetrahexyldecyl Ascorbate (THD) is an oil-soluble, lipid-based form of vitamin C. And it’s genuinely different.
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Exceptional stability: THD is far more resistant to oxidation than L-Ascorbic Acid. It won’t degrade quickly, won’t turn orange, and stays effective far longer.
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Skin-compatible pH: Oil-soluble means it doesn’t require a low pH — making it a gentler option for sensitive and compromised skin.
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Deeper penetration: THD moves through the lipid layers of skin more effectively, reaching the dermis where collagen synthesis and pigmentation actually happen.
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Converts inside the skin: Once absorbed, THD converts to active ascorbic acid within the skin cells — delivering all the benefits of vitamin C exactly where it’s needed.
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Brightening + anti-aging + antioxidant — without the irritation.
Put simply: THD does everything you want vitamin C to do, without the instability or the irritation.
So why don’t more brands use it?
Because it costs more to source and formulate with than L-Ascorbic Acid. It’s the better ingredient, just not the cheaper one. Most brands default to the version that looks good on a label rather than the one that performs in your skin.
I’ve been holding out until I found a formula I actually believed in. I think I’ve found it.