Why We Use More Than One Form of Vitamin C

Behind the Formula | Week 3

In our Ingredient Intelligence article, we looked at three forms of vitamin C—L-Ascorbic Acid, Sodium Ascorbyl Phosphate (SAP), and Tetrahexyldecyl Ascorbate (THD Ascorbate).

Each has its own strengths.

That leads to a different question:

Why would a formulator use more than one form of vitamin C in the same product?

The answer is not simply “more vitamin C.”

It is about using complementary forms that behave differently.

Different Forms Can Bring Different Strengths

Vitamin C ingredients are not interchangeable.

Some are water soluble. Some are oil soluble. Some prefer a very acidic environment, while others can perform in a more skin-friendly pH range.

That means one form may offer advantages another does not.

For example:

Sodium Ascorbyl Phosphate (SAP) is water soluble and generally more stable than L-Ascorbic Acid.

THD Ascorbate is oil soluble and can function within the lipid portion of a formula.

When two forms are used together, the goal is not duplication.

It is complementation.

Water-Soluble and Oil-Soluble Vitamin C

One important distinction between SAP and THD Ascorbate is solubility.

SAP prefers the water phase.

THD Ascorbate prefers the oil phase.

This matters because skincare formulas—and skin itself—contain both water-loving and lipid-loving environments.

Using a water-soluble and an oil-soluble form gives the formulator two different ways to incorporate vitamin C into the overall system.

That is one reason Lord & Lily uses both SAP and THD Ascorbate in Double C Brightening Serum.

But the key idea is broader than one product:

Different forms can complement one another because they behave differently.

Why Not Just Use More of One Form?

It can be tempting to think that increasing the percentage of a single ingredient is always the best approach.

But good formulation is rarely that simple.

Higher concentration can also bring disadvantages—such as irritation, instability, incompatibility, or changes in texture.

L-Ascorbic Acid is a good example.

It is highly researched, but it also typically requires a relatively low pH and can be difficult for some sensitive skin types to tolerate.

Instead of relying on one form at a higher level, a formulator may choose multiple compatible forms at appropriate levels.

The goal is balance.

More Forms Does Not Automatically Mean Better

At the same time, adding more and more forms of vitamin C is not automatically an improvement.

Three forms are not necessarily better than two.

Five are not necessarily better than three.

Every additional ingredient adds another variable to consider—stability, compatibility, processing, texture, pH, and skin feel.

This is why formulation is not simply an exercise in ingredient counting.

The better question is:

Do these ingredients have a clear reason to be together?

If the answer is no, adding more can make a formula more complicated without making it better.

The Formulation Principle

At Lord & Lily, our approach is to choose ingredients based on their function within the whole formula, rather than selecting them simply because they are popular.

Sometimes one form of vitamin C is enough.

In other situations, two complementary forms can make more sense.

The important point is that the decision should be intentional.

One ingredient may provide the foundation. Another may extend or complement its strengths.

That is the thinking behind using more than one form of vitamin C.

From the Formulator’s Bench

When I formulate, I do not ask, “How many forms of vitamin C can I put into this product?”

I ask:

What does each form contribute, and does combining them create a better-balanced formula?

If two ingredients do essentially the same job in the same way, there may be little reason to use both.

But when they bring complementary properties—such as water solubility and oil solubility—the combination can make sense.

That is formulation intelligence: not adding more, but choosing more thoughtfully.

— Lily Yang, Founder & Formulator, Lord & Lily