Preserving Liquid Soap Made with Oil and KOH

Yes, it is generally recommended to add a preservative to liquid soap made from oil saponified with KOH and dissolved in water.

Here's why:

• Water Content: The presence of water makes the product susceptible to microbial growth, including bacteria, mold, and yeast.
• Contamination Risk: During use, the soap can be exposed to microbes from the environment or hands.
• Product Stability: Microbial growth can cause spoilage, changes in color, odor, and texture, and reduce the shelf life of the product.

While the high pH of traditional soap can inhibit the growth of some microorganisms, it may not be sufficient to prevent the growth of all types, especially mold and certain bacteria. Therefore, adding a broad-spectrum preservative is a good practice to ensure the stability and safety of your liquid soap.

Finding a preservative that is effective and stable at the high pH typical of saponified soap can be challenging, as many common preservatives work best in more acidic conditions. You should look for preservatives specifically designed for high pH formulations.

Examples of broad-spectrum preservatives include Mild Preserved™ COS (effective up to pH 8), Global Guard™ 221 (effective up to pH 7), Preserve-BSB™ (effective up to pH 5.5), and NaturePreserve™ LB2 (effective up to pH 6.5). When selecting a preservative, always check its recommended pH range to ensure it is suitable for your soap formulation's pH.