THD Ascorbate
INCI · Tetrahexyldecyl Ascorbate · also THDA, vitamin C ester, oil-soluble vitamin C
How it works
Tetrahexyldecyl ascorbate (THD ascorbate) is a lipid-soluble ester of vitamin C created by attaching a fatty alcohol chain to ascorbic acid. Its lipophilic structure allows efficient partitioning into the skin's lipid-rich stratum corneum, where esterases gradually release free ascorbic acid to act as an antioxidant and support collagen-related signaling and pigment modulation.
The evidence
In vitro penetration studies indicate THD ascorbate achieves higher skin concentrations of bioavailable vitamin C compared with some water-soluble derivatives, attributed to its favorable partition coefficient into lipid membranes. It is also notably resistant to oxidation in formulation, giving it a longer shelf life than unmodified ascorbic acid. Clinical data specific to THD ascorbate is more limited than for L-ascorbic acid itself, though its mechanism and downstream conversion to active vitamin C are well documented.
Suitability
THD ascorbate suits dry and normal skin well due to its emollient, oil-soluble nature, and is considered gentle enough for sensitive skin since it avoids the low pH of pure ascorbic acid.
- Dry or sensitive skin: well suited given its non-acidic, oil-soluble format
- Oily or acne-prone skin: monitor for congestion, as it carries a mild comedogenic rating
- Pregnancy: considered a safe vitamin C option
Concentration
Formulations typically use THD ascorbate between 1% and 10%, with many serums centered around 5% to balance efficacy and texture.
Conflicts & combinations
THD ascorbate pairs well with ferulic acid and tocopherol, mirroring classic antioxidant-stabilizing vitamin C systems, and layers well under oil-based moisturizers.
- Synergistic with ferulic acid and tocopherol
- Best layered in oil- or serum-based steps rather than watery toners
- hyperpigmentation
- dullness
- anti aging
- Effective from
- 5%
- Max safe
- 10%
Is THD ascorbate better than L-ascorbic acid?
It is not strictly better, but its oil solubility allows deeper penetration and greater formulation stability, making it a strong alternative for sensitive or dry skin.
Is THD ascorbate comedogenic?
It carries a mild comedogenic rating in some ingredient databases, so those who are very acne-prone should monitor for congestion.
Can THD ascorbate be used with retinol?
Yes, oil-soluble vitamin C esters like THD ascorbate are generally considered compatible with retinol, though many routines separate them into AM and PM to reduce irritation risk.
Is THD ascorbate safe during pregnancy?
Yes, it is considered a safe vitamin C derivative for use during pregnancy.
Why is THD ascorbate more expensive than other vitamin C forms?
Its synthesis and superior stability and penetration profile generally make it a premium raw material compared with simpler vitamin C derivatives.