Toner Formulation Advice

It sounds like your toner developed a bad smell quickly, which often indicates microbial contamination. This can happen if the preservative system isn't effective enough for the specific ingredients and formula.

1. Preservation: The amount of preservative (0.5%) might be too low for a water-based product containing natural ingredients like Witch Hazel. Ensure you are using a broad-spectrum preservative suitable for this type of formula and that the concentration is adequate according to the supplier's recommendations.
2. Salicylic Acid Type: The Encapsulated Salicylic Acid you used is described as a "Wash-Off" type, intended only for products that are rinsed off. If your toner is a leave-on product, this might not be the most suitable type. Consider using a "Leave-On" type of Salicylic Acid if available, as it is designed for prolonged skin contact.
3. Adding Fragrance: To add a fresh scent similar to Biotherm, you can incorporate a fragrance oil. Based on your preference for a fresh scent, you might consider options like Fresh Morning, Fresh Rose, or Jasmine Fresh. Fragrance oils are typically added at a low concentration in toners, usually between 0.1% and 0.5%. You will likely need a solubilizer to properly disperse the fragrance oil in the water-based toner.
4. Adding Tea Tree Oil: You can add Tea Tree Oil to your toner. It has antibacterial properties and is often used in products for acne-prone skin. However, like fragrance oil, Tea Tree Oil is oil-soluble and will require a solubilizer to mix into your water-based toner. The recommended usage rate for Tea Tree Oil on facial skin is no more than 0.5%.

To prevent spoilage, always ensure proper hygiene during preparation and use an effective preservative system.