Other than optimal storage conditions (fridge, opaque pump bottle minimizing air exposure). What are best practices for formulating with Retinol?
- High viscosity - less interaction between retinol and water molecules over time.
- High oil % - Studies show that 40% oil emulsions can increase stability 2x over a 15% oil emulsion.
- Consider a 100% oil formula, use waxes to make a "salve"?
- Encapsulation through sonication with e.g. silica, make OWO formula (can be technically difficult, requires the right tools and materials).
- Antioxidants: Vitamin E, Vitamin C, BHT, BHA typically used.
- pH? What's the optimal number.
Anyone know what solvents or oils are best to improve Retinol stability? (theoretically, from studies or from experience) and what to avoid other than e.g. oxygen releasing agents and strong acids.