Formulating Mandelic Acid 15% with Witch Hazel: Preservation, Dissolution, and Residue
Question
I need some advice.
If I want to make a formulation with Mandelic Acid 15% and Witch Hazel Plus Allan (using it instead of distilled water), do I need to add an additional preservative? If so, which one should I use and at what percentage? This is because Witch Hazel Plus Allan already contains a preservative.
Is it normal for Mandelic Acid powder to take a long time to dissolve in water?
And for Mandelic Acid 15% (dissolved in water), is it normal for powdery residue to form along the edges of the bottle? (I'm asking because I haven't seen residue form along the edges of bottles in commercially available products.)
Answer
Formulation Questions: Mandelic Acid 15% + Witch Hazel Plus Allantoin
Here is information regarding your questions about formulating with Mandelic Acid 15% and Witch Hazel Plus Allantoin:
Preservative Requirement
Witch Hazel (Alcohol Free, Paraben Free) Plus Allantoin does contain Benzoic Acid as a preservative. However, when creating a formulation with 15% Mandelic Acid, it is highly recommended to add an additional broad-spectrum preservative to ensure the stability and safety of the final product. The effectiveness of the preservative in Witch Hazel alone might not be sufficient for the entire formulation, especially at a high concentration of Mandelic Acid.
Consider using a broad-spectrum preservative that is effective in the acidic pH range, such as:
- Mild Preserved™ COS: Recommended usage rate is 0.75-1.5%. It is effective in a pH range of 2-8.
- NaturePreserve™ Ultra: Recommended usage rate is 0.75-2.0%. It is effective in a pH range of 3-6.
Always perform a challenge test on your final formulation to confirm the effectiveness of the preservative system.
Mandelic Acid Dissolution
It is normal for Mandelic Acid powder to take time to dissolve in water, especially at higher concentrations like 15% and at room temperature. Mandelic Acid's solubility in water is limited (around 13% at 25°C). To achieve a 15% solution, you might need to gently heat the water (below 60°C) or use a co-solvent like ethyl alcohol to help it dissolve completely.
Powdery Residue
The formation of powdery residue along the edges of the bottle in a 15% Mandelic Acid solution is likely due to undissolved Mandelic Acid or recrystallization. Since the solubility in water at room temperature is around 13%, a 15% solution is supersaturated at this temperature, making it prone to precipitation or recrystallization, especially with temperature changes or evaporation. Commercially available products may use different solvents, higher manufacturing temperatures, or different forms of Mandelic Acid to prevent this issue.
