Formulation Questions: pH Adjustment, Alpha Arbutin, and Phenoxyethanol in Serum/Cream
Question
I am developing a serum/cream formulation containing the following:
- Hyaluronic Acid (two types) at 0.1% each
- Alpha Arbutin
- Phenoxyethanol at 0.2%
I have the following questions regarding the formulation process:
- Can I use Citric Acid to adjust the pH down to 5.5, especially considering the presence of Hyaluronic Acid?
- What is the correct procedure for adding Alpha Arbutin? Should it be added before or after the Hyaluronic Acid is fully dissolved?
- Is Phenoxyethanol soluble in water? How should it be added to the formulation?
- Is using Phenoxyethanol at a concentration of 0.2% sufficient for preservation compared to 0.5%? What is the typical recommended usage range for Phenoxyethanol?
Answer
Based on the previous conversation:
pH Adjustment with Citric Acid
Yes, you can use Citric Acid to adjust the pH of your serum/cream down to 5.5, even with Hyaluronic Acid (both types) present at 0.1% each. As the staff mentioned, since your other ingredients are likely neutral or slightly acidic, adding Citric Acid will lower the pH quite quickly. It is crucial to add it in very small amounts at a time and check the pH frequently. If you accidentally lower the pH too much, you can use a base like Triethanolamine to raise it back up.
Adding Alpha Arbutin
You can add Alpha Arbutin either before or after the two types of Hyaluronic Acid have fully dissolved. The main consideration when working with Hyaluronic Acid is ensuring it is completely dissolved, which can take some time.
Phenoxyethanol Preservative
Regarding Phenoxyethanol:
- Solubility: Yes, Phenoxyethanol is soluble in water and is typically added to the water phase of a formulation. Gentle heating can sometimes help it dissolve more easily.
- Concentration (0.2% vs 0.5%): Using Phenoxyethanol at 0.2% may not provide the same level of preservation or broad-spectrum efficacy as using it at 0.5%. Preservative effectiveness is concentration-dependent. A lower concentration might not be sufficient to inhibit the growth of all types of microorganisms effectively or for the desired shelf life, as mentioned by the staff. The recommended usage range for Phenoxyethanol is typically 0.5% to 1%. Using it below the recommended minimum (like 0.2%) significantly reduces its ability to protect the product from microbial contamination over time.