Serums vs creams: what's the real difference?

Clients often ask about the difference between serums and creams, assuming that serums are always more potent or better absorbed. 

Dr Ronit Segev debunks some common myths and provides clear explanations to help you confidently educate your clients.

How can I explain the difference between serums and creams to clients?

To give a clear and practical answer about the differences, let’s first clarify some common myths. When I ask my students about serums, I get a range of answers. Let’s critically examine some of these statements.

Myth: serums are more concentrated

The manufacturer determines the concentration of active ingredients in a cream or serum. For example, if a manufacturer creates a cream with 3% Matrixyl, what’s the difference between that and a 3% Matrixyl serum?

Many creams are formulated with active ingredients at the optimal concentrations for efficacy, as supported by clinical studies.

A common belief is that serums have higher concentrations of active ingredients than creams, even if the cream contains the same actives. But why is that?

Let’s understand the term “therapeutic window” of active ingredients. If a vitamin, peptide or other ingredient has a therapeutic window of 3-5%, it means:

• At 2%, the ingredient won’t improve the skin.
• At 3%, it will start showing benefits.
• At 4%, the improvement will be slightly more pronounced, and at 5%, even more so.
• But this doesn’t mean that 10% will necessarily yield better results.

With active ingredients, more is not always better. The precise concentration delivers the results. If a manufacturer aims to ensure efficacy, trust that they’ll include the active concentration – whether in a cream, serum or ampoule.

So, what’s the difference between a 1% retinol cream and a 1% retinol serum?

Myth: serums have smaller molecules

Smaller molecules of what, exactly? The entire serum? Just the active ingredients? And why can’t a manufacturer use small molecules in a cream as well?

The liquid, lightweight texture of a serum isn’t necessarily due to smaller molecules. In fact, not all of the cream or serum needs to penetrate deep into the skin – only the active ingredient(s) need to be absorbed.

For instance, if the active ingredient is retinol, its size doesn’t change between a cream and a serum. This applies to both active and inactive ingredients.

Myth: serums help creams penetrate the skin

As a biologist, I’m not aware of any microscopic mechanisms that allow serums to bind large molecules and pull them into the skin.

Similarly, there are no known methods to make molecules larger than 500 Daltons (the size limit for penetrating the stratum corneum) pass through the skin.

For example, hyaluronic acid in a serum doesn’t penetrate the skin because of any special delivery properties of the serum.

In short, molecules penetrate the skin based on their size, whether they are in a cream or serum. The difference lies in texture or consistency.

Serums are liquid, while creams have a richer texture. I’ve seen serums without any active ingredients and creams that are full of them.