Formulation Advice for Sensitive Skin, Eye Area, and Preservation

Here is a summary of the information regarding your questions about cosmetic formulations, based on the discussion:

Suitability for Oily Skin

Using Mild Preserve 0.8% + Propylene Glycol 5% + Phenoxyethanol 0.2% for oily skin: If your formula already contains an emulsifier such as Pro Polymer or other types of cream makers, adding Propylene Glycol may not be necessary. Propylene Glycol acts as a humectant and solvent, and its inclusion depends on the overall formula and desired feel. If the formula has sufficient humectants or is designed to be lightweight for oily skin, 5% Propylene Glycol might feel heavy, especially when combined with the moisturizing properties of Mild Preserve. Consider if the emulsifier system itself provides enough solvency and texture without the need for additional Propylene Glycol.

Preservation for Eye Area Products

For eye area products, ensuring sufficient preservation is crucial due to the sensitivity of the area and potential for microbial contamination. The combination of Phenoxyethanol 0.1% + Propylene Glycol 5% + Mild Preserve 0.4% might not be sufficient for broad-spectrum protection, especially against mold and yeast, based on the efficacy data discussed. The recommendation for preservatives not exceeding 0.5% often applies to ingredients known to cause irritation; Mild Preserve and Eye Preserve are generally considered less irritating.

• Mild Preserve: Lab tests show that Mild Preserve at 1.0% is effective in controlling bacteria, yeast, and mold in an oil-in-water lotion. This concentration is considered sufficient for broad-spectrum preservation, including for products used on the face and around the eyes.
• Eye Preserve: This preservative was specifically developed for eye safety, even used in contact lens solutions. For products sold in Thailand and Europe, Eye Preserve can be used up to 1.5%. At this 1.5% concentration, it provides sufficient broad-spectrum control alone. If using Eye Preserve at a lower concentration (e.g., 0.5% for products sold in Japan), it needs to be combined with other preservatives to ensure full efficacy, particularly against mold and yeast.

Comparing Mild Preserve and Eye Preserve, neither is typically considered irritating like some other preservatives. Mild Preserve offers humectant properties, while Eye Preserve has extensive safety data specifically for eye applications.

Mild Preserve Solubility in Pro Polymer Gel

Mild Preserve is soluble in glycols. When incorporating Mild Preserve into a water-based formula, including one using Pro Polymer as a gel maker or emulsifier, it is recommended to first dissolve the Mild Preserve in a suitable glycol (such as Propylene Glycol or Ethoxydiglycol) at a ratio of at least 10 parts glycol to 1 part Mild Preserve. This glycol pre-dispersion step helps ensure it fully incorporates into the water phase. You cannot typically dissolve Mild Preserve directly into a finished gel without this step.

Equipment Cleaning

The method of rinsing and wiping mixing equipment (spoons, beakers) with alcohol and then air drying is sufficient for killing germs and ensuring cleanliness for your formulations.

Mild Preserve Solidification in Refrigerator

Concentrated Mild Preserve raw material can solidify if stored below 15°C. However, when diluted into a finished formula at a typical usage concentration (not exceeding 2.0%), it will not solidify when stored in the refrigerator.

Pro Polymer Concentration for Mild Preserve

Regarding whether 0.2% Pro Polymer is sufficient to incorporate 0.5% Mild Preserve, while there isn't a definitive test result provided for this specific combination, the general method is to pre-dissolve Mild Preserve in a glycol before adding it to the water phase containing Pro Polymer. This method helps ensure proper incorporation regardless of the Pro Polymer concentration used for gelling or emulsification.

Reducing Preservative Concentration with Refrigeration

While refrigeration can help extend the life of a product by slowing microbial growth, it is generally not recommended to reduce the concentration of your chosen preservative(s) below their proven effective minimum inhibitory concentrations (MIC) or recommended usage levels. The standard recommended concentrations for Mild Preserve (1%) and Eye Preserve (up to 1.5%) are designed to provide adequate preservation under typical storage and usage conditions, and relying solely on refrigeration might not guarantee microbial stability, especially if the product is occasionally left outside the refrigerator.

Combining Preservatives for Eye Area

If using Eye Preserve at less than 1.5% (e.g., 0.5%), combining it with another preservative is necessary to achieve broad-spectrum protection. Mild Preserve at 1% has been shown to be effective for broad-spectrum control, including for the eye area. Therefore, using Mild Preserve at 1% alone is a viable option for preserving eye area products. If you choose to combine, the specific concentrations would need to be tested for efficacy, but using Eye Preserve at 1.5% alone or Mild Preserve at 1% alone are established effective methods based on the provided information.