Serum Thickening Advice

It sounds like you have a great formulation aimed at oil control and brightening with ingredients like Matrixyl 3000, Azelaic Acid, Allantoin, Vitamin B3 (Niacinamide) + N-Acetyl Glucosamine, MSM, Zinc PCA, and Licorice Extract. It's common for formulations with these water-soluble actives to be quite liquid, as these ingredients themselves don't significantly increase viscosity.

To achieve a serum consistency, you will need to incorporate a gelling agent or thickener into your formula. Here are a few suitable options:

• Xanthan Gum: A natural gum that is effective at low concentrations (typically 0.1-0.5%). It's relatively easy to use but can sometimes result in a slightly sticky feel.
• Hydroxyethylcellulose (HEC) or Hydroxypropylcellulose (HPC): These are cellulose-based thickeners that provide a smooth texture and are generally tolerant of electrolytes and varying pH levels, which is good for your formula containing Zinc PCA and having a pH of 4.3. Use typically ranges from 0.2% to 2%.
• Sclerotium Gum: Another natural gum that can provide a nice feel, often less sticky than Xanthan Gum. Use at similar concentrations to Xanthan Gum (0.1-0.5%).

How to add a thickener:

1. Start with a low percentage of your chosen thickener.
2. Disperse the thickener powder evenly in the water phase of your formulation while stirring continuously to prevent clumping. Some thickeners benefit from being dispersed in a small amount of glycerin or other non-solvent first.
3. Continue stirring and allow adequate time for the thickener to hydrate fully. This can take some time depending on the specific thickener.
4. Check the viscosity and add more thickener gradually if needed, repeating the dispersion and hydration steps until you reach your desired serum consistency.

Choosing the right thickener and finding the correct percentage will require some experimentation, but starting with one of the options above should help you achieve the desired texture for your serum.