Why Preservatives Are Added in the Final Step and When to Add Water-Soluble Ones

Preservatives are often added in the final step of a cosmetic formulation for several important reasons:

• Temperature Sensitivity: Many preservatives can degrade or lose effectiveness when exposed to high temperatures used during the heating phase of a formulation. Adding them after the mixture has cooled down ensures their stability.
• pH Sensitivity: Preservatives are typically effective within a specific pH range. Adding them at the end allows for the pH of the final product to be adjusted to the optimal range for the preservative before it is incorporated.

However, some water-soluble preservatives can be added during the water phase, provided their properties are suitable for the formulation's process. It is essential to check the manufacturer's instructions for each specific preservative regarding:

• Maximum Temperature: Some water-soluble preservatives can withstand higher temperatures (e.g., NaturePreserve™ Ultra is heat tolerant), while others must be added below a certain temperature (e.g., Global Guard™ 221, Mild Preserved™ COS, and NaturePreserve™ LB2 recommend adding below 45-50°C, and Preserve-BSB™ below 80°C).
• pH Range: Ensure the pH of the water phase (and the final product) falls within the effective range of the preservative.

Always refer to the specific usage instructions for the preservative you are using to determine the correct mixing method and temperature/pH conditions. Performing a challenge test on the final product is also crucial to confirm the preservative's effectiveness.