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Tetrahexyldecyl Ascorbate (THD-C) Vitamin C
Quick Reference
INCI Name: Tetrahexyldecyl Ascorbate
Common Names: THD Ascorbate, THDA, THD-C, oil-soluble vitamin C, lipid-soluble vitamin C
Category: Antioxidant, vitamin C derivative
Source: Synthetic (derived from L-ascorbic acid)
Nubeean Concentrations: 5%, 10%, 20%, 30%
Carrier System: Oil soluble
Skin Types: All skin types, particularly suited to sensitive skin, mature skin and those who cannot tolerate L-ascorbic acid
Cautions: Higher concentrations (20-30%) may cause initial redness or peeling, particularly in sun-damaged areas. Patch test first with higher strengths.
What It Is
Tetrahexyldecyl ascorbate is an oil-soluble form of vitamin C that was developed to overcome the significant limitations of traditional L-ascorbic acid. Where L-ascorbic acid is water-soluble, unstable and requires a very acidic pH (below 3.5) to penetrate skin - often causing irritation - THD-C is stable at neutral pH, easily penetrates the skin's lipid barrier and converts to active L-ascorbic acid once inside the skin cells.
The molecule works because of its esterified structure: four fatty chains attached to the ascorbic acid core make it lipophilic (fat-loving), allowing it to slip through the stratum corneum - the skin's waxy outer barrier - with ease. Research demonstrates that THD-C penetrates approximately three times more effectively than L-ascorbic acid at the same concentration, reaching both the epidermis and dermis where it can exert its collagen-supporting effects.
This matters for two reasons. First, you get more vitamin C where it's needed. Second, you can use it comfortably every day without the stinging, redness and pH sensitivity that makes L-ascorbic acid difficult for many people to tolerate.
How It Works
Enzymatic conversion. THD-C is a pro-vitamin - it doesn't work as vitamin C directly. Once it penetrates the skin, cellular esterase enzymes cleave off the fatty chains, releasing active L-ascorbic acid inside the cells where it's needed. This intracellular delivery mechanism means the vitamin C arrives protected, avoiding the oxidation that plagues topical L-ascorbic acid formulas.
Collagen synthesis support. Vitamin C is an essential co-factor for the enzymes that produce and crosslink collagen. Without adequate vitamin C, collagen formation is impaired. THD-C supports this process by ensuring vitamin C reaches the dermal fibroblasts responsible for collagen production. Research shows THD-C can increase expression of collagen types I and III - the primary structural collagens in skin.
MMP inhibition. Matrix metalloproteinases (MMPs) are enzymes that break down collagen and other structural proteins. UV exposure and aging both upregulate MMP activity. THD-C has been shown to inhibit MMP-1 and MMP-7 activity, helping preserve existing collagen while supporting new production.
Antioxidant protection. Once converted to L-ascorbic acid, THD-C provides free radical scavenging activity, protecting cells from UV-induced oxidative damage. However, research indicates that THD-C alone is a relatively poor antioxidant on the skin surface - its strength lies in delivering vitamin C inside cells rather than surface-level protection.
Melanin regulation. Vitamin C inhibits tyrosinase, the enzyme responsible for melanin production. By reducing melanin synthesis, THD-C can help fade existing hyperpigmentation and prevent new dark spots from forming. Clinical studies have demonstrated significant improvement in skin tone evenness with regular use.
Benefits
Primary Benefits
THD-C supports collagen production by ensuring vitamin C reaches the dermal cells where collagen synthesis occurs. Over time, this can improve skin firmness and reduce the appearance of fine lines. The ingredient also provides meaningful brightening effects through tyrosinase inhibition, helping to even out skin tone and fade hyperpigmentation.
Secondary Benefits
Because THD-C is stable and works at neutral pH, it's far gentler than L-ascorbic acid - making it accessible to sensitive skin types who previously couldn't tolerate vitamin C. The oil-soluble nature also means it integrates beautifully into anhydrous formulations, acting as both an active ingredient and part of the moisturising oil phase. Unlike water-soluble vitamin C that evaporates off the skin, THD-C in a squalane base provides lasting hydration.
Skin Concerns Addressed
THD-C addresses visible photoaging including fine lines, uneven texture and loss of firmness. It's effective for hyperpigmentation from sun damage, post-inflammatory marks and melasma (though melasma requires comprehensive management). It can help improve the appearance of acne scars through its collagen-supporting mechanism.
Who Benefits Most
Mature and sun-damaged skin.
Hyperpigmentation concerns.
Those who want simplicity. If you prefer a streamlined routine, a THD-C serum in squalane replaces both your vitamin C treatment and your facial oil.
Fair & sensitive skin
Research and Evidence
Clinical studies have demonstrated that 30% THD-C formulations improve signs of photoaging including pigmentation, fine lines and overall skin quality after 6 weeks of twice-daily use. Research also shows that THD-C combined with acetyl zingerone provides superior collagen production and antioxidant effects compared to either ingredient alone - this is why we recommend using our THD-C serums with our Hydrate + Protect | Skin Shield spray which contains acetyl zingerone.
The penetration advantage of THD-C over L-ascorbic acid has been confirmed in membrane studies, showing approximately threefold greater penetration at equivalent concentrations.
Frequently Asked Questions
What is the difference between THD-C and regular vitamin C (L-ascorbic acid)? THD-C is oil-soluble and stable, while L-ascorbic acid is water-soluble, unstable and requires a very low pH to work. THD-C penetrates skin more effectively, converts to active vitamin C inside cells, and is far gentler - making it suitable for sensitive skin types who can't tolerate traditional vitamin C serums.
Can I use THD-C with copper peptides? Yes. THD-C is oil-based while copper peptides are water-based - they occupy different phases and don't meaningfully interact on skin. You can apply copper peptide serum first, let it absorb, then follow with THD-C as your final oil step.
Should I use THD-C morning or night? Either works well. THD-C is photostable so it's safe for daytime use (always with sunscreen). Some people prefer morning for the antioxidant protection, while others prefer evening to pair with other treatments. Using it twice daily is also an option, particularly with lower concentrations.
What concentration should I start with? Start with 10%, especially if you have sensitive skin or haven't used vitamin C before. After 4-12 weeks, you can increase to 20% if desired. Reserve 30% for experienced users targeting significant photoaging.
How is this different from bakuchiol products? THD-C is vitamin C; bakuchiol has retinol-like effects. They work through different mechanisms and can be used together. Our combination serums (Sensitive C PLUS and the +Bakuchiol versions) provide both benefits in one product.
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