Preservative Recommendation for Water-in-Silicone SPF Serum

For a Water-in-Silicone/Oil SPF Serum using Silky Serum Base Plus and Titanium Zinc NanoLiquid™ DEC, I recommend the following preservative options that meet your criteria (liquid, odorless, colorless, and gentle on the eyes):

1. Primary Recommendation: Mild Preserved Eco™

This is the most suitable choice for your specific base. It is a "preservative-free" system (according to FDA definitions) that is highly gentle and does not irritate the skin or eyes.

• Characteristics: Clear liquid, completely odorless, and colorless.
• Why it fits: It is explicitly recommended in the example formulations for Silky Serum Base Plus. It also acts as a humectant, adding moisture to the serum.
• Usage Rate: 1.0% - 1.5% in the final formula.

2. Specialized Option: Eye Preserved™ (PHMB)

If your serum is specifically targeted for the delicate eye area or for users with extreme sensitivity, this is an excellent alternative. It was originally developed for contact lens solutions.

• Characteristics: Clear liquid, odorless, and colorless.
• Why it fits: It is designed to be non-toxic and non-irritating to the eyes.
• Important Note: This preservative is cationic. It should not be used if you plan to add anionic ingredients like Hyaluronic Acid or Xanthan Gum to your serum, as they will clump together.
• Usage Rate: 0.5% - 1.5%.

Important Formulation Tips for Stability

Since you are creating a Water-in-Silicone (W/Si) emulsion with these specific ingredients, please keep the following in mind:

• Emulsion Stabilizer: It is highly recommended to add 1% Magnesium Sulfate to your water phase. This is crucial for preventing the serum from separating over time, especially when incorporating heavy mineral sunscreens like Titanium Zinc NanoLiquid™ DEC.
• Mixing Method: Always add the water phase (containing the water and magnesium sulfate) to the silicone phase (containing the Silky Serum Base Plus and sunscreens) very slowly, in small increments, while stirring or blending continuously.
• Sunscreen Incorporation: Titanium Zinc NanoLiquid™ DEC should be mixed into the oil/silicone phase before adding the water.

Relevant Products:

• Silky Serum Base Plus (Emulsifier Base)
• Titanium Zinc NanoLiquid™ DEC (Physical Sunscreen)
• Mild Preserved Eco™ (Recommended Preservative)
• Eye Preserved™ (Alternative Preservative for Eyes)
• Magnesium Sulfate (Stabilizer)