If You Have Sensitive Skin, This Form of Vitamin C Is For You

It’s clear that LAA, in its traditional form, can be problematic, both for formulators and consumers. “LAA has been sold as the do-all of skin care. But out of a hundred LAA serums out there, there are probably two doing what they need to do,” says Koestline. “And it is pretty upsetting. It’s not what people have sold it to be.”

A Better Way to Reap the Benefits of Vitamin C

When it comes to vitamin C in skin care, there are two categories: active and inactive. The only active form is LAA. All other forms of vitamin C are considered inactive because they have to be converted to LAA within the skin before they can get to work.

THDA is one of the many such inactive derivatives of vitamin C on the market that aims to overcome the deficiencies of LAA. Others include ascorbyl palmitate, ascorbyl glucoside, 3-O ethyl ascorbic acid, sodium ascorbyl phosphate, and magnesium ascorbyl phosphate. “I consider LAA to really be pure, while the others are substantially modified and structurally very different molecules,” says Dobos. While usefulness and efficacy vary amongst these derivatives, many of the experts we spoke to were clear that THDA came out on top.

As compared to LAA, THDA penetrates better and remains more stable—because it’s formulated to be that way. “LAA is inherently unstable and prone to oxidation because its structure readily reacts with oxygen in the atmosphere. THDA addresses this by chemically modifying ascorbic acid with a lipid-based tail during manufacturing, which stabilizes the molecule and makes it oil-soluble,” says Koestline. This modification not only improves THDA’s stability but also allows it to integrate smoothly into oil-based formulations.

And lastly, since THDA does not convert into active LAA until it comes into contact with the oils on the skin, it results in a gentler release of the active ingredient. “Unlike LAA, which is water-soluble and requires a low pH to remain stable, THDA is pH-independent. This makes it less irritating and suitable for sensitive skin, as it bypasses the need for an acidic environment, which can sometimes cause redness or stinging,” says Dr. Liu.

This allows THDA to be formulated in products with a skin-neutral or slightly acidic pH, which is less likely to disrupt the skin barrier or cause irritation. For example, Rouleau’s Vitamin C&E Treatment, which uses THDA, has a pH level of 5.3, as compared to some brands using LAA, which can have a pH of 3.5 or lower.