But not every vitamin C formula is created equal. While water-soluble L-ascorbic acid is the widely researched and used form of vitamin C (it’s the type found in popular products like my beloved Klair’s Freshly Juiced Drop Vitamin C Serum, Skinceuticals C E Ferulic, and Drunk Elephant’s C-Firma), it does have a few disadvantages: For one, it’s incredibly unstable — if it’s not stored in an airtight container in a cool, dark place, it’s expires quickly. And since L-ascorbic acid tends to be formulated at a relatively low pH level (around 3.5), it can be irritating on the skin, and can lead to breakouts, bumps, and irritation.
Late one evening recently, while poking around Reddit threads on r/SkincareAddiction, I found a group of vitamin C obsessives raving about the benefits something called tetrahexyldecyl ascorbate (THD ascorbate), a “lipid soluble” (meaning it dissolves in oils) form of vitamin C that, they claimed, was gentler, more stable, and — they thought, at least — even more effective than the kind found in my Klair’s.
A few hours spent researching “tetrahexyldecyl ascorbate” later, I discovered that many skin-care companies, including Biossance and The Ordinary, have recently been using THD ascorbate instead of L-ascorbic acids in their vitamin C serums. Early research has shown that not only is it indeed more shelf stable, but that it also works exceptionally well in lifting sun spots and hyperpigmentation, and can potentially penetrate even deeper into the skin than the L-ascorbic kind (meaning it can therefore more intensely stimulate the body’s collagen production). And thanks to its fatty acid base and higher pH level (THD is usually formulated around 5.5), THD ascorbate products also tend to be gentler and significantly more hydrating on the skin. All of which basically means, if you’re someone who has wanted to reap the many, many benefits of vitamin C, but who has been afraid it would break or dry you out, or if you’re like me and have tried vitamin C and it has broken or dried you out, a THD ascorbate product is a really, really good choice. Below, my favorite products that use THD.
I’ve tried about three or four THD ascorbate products. But my favorite is easily this lightweight yet deeply nourishing face oil from Biossance. Along with the THD ascorbate, this oil uses plant based squalene (a naturally occurring emollient that helps lock in moisture) and chios crystal oil (which plumps and firms the skin) to hydrate, illuminate, and replenish the skin in a gentle and nonirritating way. The serum has both immediate and long-term effects: After applying it, it gives a beautiful dewy and nourished (but not greasy) glow that’s perfect for bare skin days or for wearing under concealer. And after a few months of consistent use, I noticed that a few spots along my jawline left over from a bad hormonal breakout had also begun to fade away. And I am not the only fan: Jonathan Van Ness, Desi Perkins, and Kehlani also swear by it. I apply a few drops of this in the morning onto clean skin, then follow up with my Purito SPF.
This cheaper alternative from The Ordinary uses a blend of vitamin F and THD ascorbate. With consistent daily use, you’ll notice smoother and more radiant skin. The formula feels a little thicker on the skin than the above, but it’s a wonderful dupe (at about a quarter of the price!) for achieving that that radiant glow — and it’s great for fading sun spots and hyperpigmentation left behind. Skin-care guru Gothamista is a fan of this one, which means it’s really good.
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