Formulation Review

Regarding the formulation you provided:

• 10% L-ascorbic acid
• 1% Glutathione
• 1% Pro Polymer
• 0.5% Phenoxyethanol
• 87.5% Water

And your questions about its usability, pH adjustment, and shelf life concerning Vitamin C degradation.

Usability

Yes, this formulation can be mixed, as confirmed by the staff's reply.

pH Adjustment

The staff mentioned that pH adjustment is not necessary. However, for optimal stability and effectiveness of both L-ascorbic acid and Glutathione, adjusting the pH is highly recommended. L-ascorbic acid is most stable in a low pH environment, ideally between 2.0-4.0 (and cosmetic products applied to the skin must have a pH of at least 3.5 according to FDA guidelines). Glutathione is also most stable within a pH range of 3-6. Therefore, adjusting the final formulation's pH to be between 3.0 and 4.0 would significantly help maintain the stability of these active ingredients.

Shelf Life and Vitamin C Degradation

The staff correctly stated that L-ascorbic acid degradation begins immediately upon mixing in water and is a gradual process. L-ascorbic acid is inherently unstable in aqueous solutions, meaning it will lose potency over time. While the inclusion of Glutathione at a 1:10 ratio to L-ascorbic acid can help improve stability, as indicated in the Glutathione product description, the formula's shelf life for retaining high Vitamin C efficacy is still limited.

Storing the product properly (in a refrigerator at 6-8°C, away from sunlight and heat, with the lid tightly sealed) is crucial to slow down the degradation process. However, expecting it to maintain significant efficacy for a full month might be optimistic depending on the exact storage conditions and the initial quality of the ingredients. Degradation will occur continuously.

For longer-lasting Vitamin C efficacy, considering more stable derivatives like Ethyl Ascorbic Acid, Ascorbyl Glucoside, Magnesium Ascorbyl Phosphate (MAP), or Sodium Ascorbyl Phosphate (SAP) might be beneficial, although their efficacy profile can differ from L-ascorbic acid.

Pro Polymer acts as a thickener to create the gel texture, and Phenoxyethanol is included as a preservative to prevent microbial growth, which is important for the overall safety and shelf life of the product, but does not prevent the chemical degradation of Vitamin C.

In summary, the formulation can be made, but adjusting the pH to 3.0-4.0 and storing it correctly are vital for maximizing the limited stability of the L-ascorbic acid. Be aware that efficacy will decrease over time.