Tetrahexyldecyl Ascorbate (THD): The Oil-Soluble Vitamin C

Most vitamin C in skincare dissolves in water. Tetrahexyldecyl ascorbate, or THD, dissolves in oil. That one difference makes it one of the gentlest and most versatile forms of vitamin C you can use.

What is THD?

THD is vitamin C bonded to fatty acids, which makes it oil-soluble. Because of that, it can go into creams, balms and oils, where water-soluble vitamin C can't. It's also naturally stable, so it stays effective for longer in a formula [1][2].

Why skin likes it

• Very gentle. THD doesn't need a low pH to work, so it's far less likely to sting or irritate than pure ascorbic acid. That makes it a go-to for sensitive skin, and for anyone who has had a bad experience with vitamin C before.
• Works with your skin's oils. Being oil-soluble helps it blend into the skin's natural lipid layer [2].
• Stable. It resists breaking down in light and air, so you get the benefit from the first use to the last.
• An antioxidant for everyday defence. Like all vitamin C, it helps protect skin from the free radicals behind dullness and uneven tone [1].

What it does for uneven tone

Vitamin C slows tyrosinase, the enzyme that starts pigment production [1]. With steady use, THD helps skin look brighter and more even, including the marks that breakouts leave behind. As with every brightening ingredient, daily sunscreen is what protects the progress.

THD vs other forms of vitamin C

• L-ascorbic acid: the most researched, but unstable and often irritating
• [Sodium ascorbyl phosphate](/blog/sodium-ascorbyl-phosphate): water-soluble and gentle, and a good fit for serums
• [3-O-ethyl ascorbic acid](/blog/3-o-ethyl-ascorbic-acid): stable and gets into the skin well, in serums and cleansers
• THD: oil-soluble and very gentle, the natural fit for creams and oils

Many good routines combine more than one form, each in the texture where it works best.

How to use it

• Morning or night, as part of your moisturizing step.
• Layer it with a water-based vitamin C serum for a double dose of brightening support.
• Sunscreen every morning, SPF 30 or higher.
• Patience: 8 to 12 weeks of steady use.

Where you'll find THD at Gleamin

THD helps give our Advanced Brightening Moisturizer its vitamin C, working alongside three ceramides, hyaluronic acid and turmeric. It's a gentle daily boost that pairs with the 15% vitamin C in our Superactive Serum. Shop it in our Amazon store.

References

1. Al-Niaimi F, Chiang NYZ. "Topical vitamin C and the skin: mechanisms of action and clinical applications." Journal of Clinical and Aesthetic Dermatology (2017). PMC5605218
2. Stamford NPJ. "Stability, transdermal penetration, and cutaneous effects of ascorbic acid and its derivatives." Journal of Cosmetic Dermatology (2012).

This article is for general information and isn't medical advice. If you have a skin condition or concern, talk to a doctor or dermatologist.