DIY Serum for Oily, Sensitive, Acne-Prone Skin: Mixing Steps and Preservation

Based on your revised formula and the previous discussion, the mixing steps you outlined are correct.

1. Combine Vitamin B3, n-acetyl glucosamine, and Zinc PCA with the water, stirring each until fully dissolved before adding the next.
2. Add Hyaluronic Nano Molecule to the mixture. Shake and refrigerate for at least 3 hours, or until fully dissolved.
3. Incorporate Hydro Gel, stirring until the mixture is uniform.
4. Add Mild Preserved and stir until blended.
5. Finally, add Pro Polymer and mix or shake thoroughly until the desired gel texture is achieved. Note that Pro Polymer may take some time and thorough mixing to fully hydrate and form a smooth gel.

Importance of Preservatives

It is essential to include a preservative in any water-based skincare product, especially DIY formulations. Water is a breeding ground for microorganisms like bacteria, mold, and yeast, which can spoil the product and cause skin infections. Storing the product in the refrigerator alone is not sufficient to prevent microbial contamination for long-term use.

You have wisely included Mild Preserved in your formula. This is a good choice for sensitive skin and provides broad-spectrum protection.

With a proper preservative like Mild Preserved used at the recommended concentration (typically 0.75-1.5% for Mild Preserved™ COS) and stored correctly (at room temperature, away from direct sunlight and heat, with the lid sealed), your serum should have a shelf life of at least 2 years.

Without a preservative, even with refrigeration, the shelf life would be very short, likely only a few days to a week or two, depending heavily on the cleanliness of your workspace, equipment, and ingredients. It is highly recommended to always use a suitable preservative in water-based DIY skincare products for safety and stability.

Your chosen ingredients are beneficial for your skin type:

• Vitamin B3 (Niacinamide) and n-acetyl glucosamine help strengthen the skin barrier.
• Hyaluronic Nano Molecule and Hydro Gel provide lightweight hydration without a heavy feel.
• Zinc PCA helps manage oiliness and soothe skin.
• Pro Polymer creates the lightweight gel texture you prefer.

Always perform a patch test before applying a new product to your entire face. Monitor your skin's response and adjust usage as needed, especially when combining with acne treatments that can cause dryness or irritation.