LAB NOTES & SAFETY NOTICE
These are personal experiments for educational use only— not instructions and not for commercial or consumer use. By proceeding, you assume all risks related to safety, testing, and regulatory compliance.
[Full Legal Disclaimer & Safety Requirements]
We’ve talked about how lotions are formulated, but what about serums? What exactly are they, and how are they generally put together? 🙂
Serums are products with a few distinctive characteristics:
-
they tend to be very light systems (often associated with a low fat content, usually around 2% and rarely above 4%),
-
they are typically fluid rather than creamy,
-
they contain a high concentration of active ingredients,
-
they are often formulated without heating (largely as a consequence of the points above),
-
their role is usually described as providing an extra “boost” of targeted ingredients to the skin.
In that sense, serums and creams are often thought of as having different purposes. Creams are mainly associated with emollience and hydration, while serums are generally linked to delivering higher levels of specific actives such as vitamins, antioxidants, or anti-aging ingredients. Wanting a serum to behave like a rich moisturizing cream is a bit like expecting to bake a cake without an oven — different products, different goals 🙂
General structure of a serum
Even though serums are lighter than lotions, they are often still discussed in terms of phases. The phases are similar to those used for lotions, but their composition is usually a bit different.
Phase A
Phase A is commonly water-based and may include ingredients such as water, glycerin, and sometimes a gelling agent. Whether a gelling agent is present — and which one — depends on the type of serum and the ingredients involved.
One aspect often considered when choosing a gelling agent is how well it tolerates salts or more challenging active ingredients. Some gelling agents are known to be sensitive in this respect, while others are generally regarded as more robust. Xanthan gum and hydroxyethylcellulose, for example, are frequently mentioned in this context. Hydroxyethylcellulose, in particular, forms its gel only at elevated temperatures, which has implications for how heat-sensitive ingredients are handled later on.
Phase B
The oil phase in a serum is usually kept very small. References often mention a total oil-soluble content somewhere between about 1.5% and 4%, including oil-soluble active ingredients such as vitamin E. In other words, oil-soluble actives are typically counted as part of the overall “fat” portion of the serum.
To keep a serum fluid and lightweight despite the presence of oils, formulators often rely on emulsifiers or solubilizers that work at room temperature and remain liquid. In many discussions, this is where a combination of a more lipophilic emulsifier and a more hydrophilic one is mentioned.
In some cases, solubilizers are used instead of traditional emulsifiers, especially when the oily portion is very small. Solubilizers are commonly described as surfactant-based materials capable of dispersing tiny amounts of oil into a much larger water phase. When oil levels are extremely low (around 1–1.5%), some serum systems are even described as working without added emulsifiers or solubilizers at all, resulting in a very simple, single-phase product.
Phase C
In many serum formulations, the distinction between Phase C and Phase A becomes less important. Active ingredients are often incorporated directly into the water phase, unless there is a specific reason not to do so — for example, when heat is required earlier in the process and the actives are heat-sensitive.
Active ingredients in serums
One of the defining features of serums is the relatively high level of active ingredients they contain. In some cases, the active itself can even contribute to the structure of the product. A commonly cited example is hyaluronic acid, which can act both as an active ingredient and as a structuring or gelling component, allowing for very simple serum systems.
That’s a general overview of how serums are usually described and categorized.
If you feel like something important is missing, or you’d like to zoom in on a specific type of serum, just let me know 🙂
Have a great day! 😄
IT'S ALL IN MY HANDS 