Preservatives for Cold Process Soap

For cold process oil soap, choosing a preservative can be a bit tricky because the soap naturally has a high pH (alkaline). Many common cosmetic preservatives work best in a more acidic or neutral pH range.

Based on the available options and their pH ranges, here are a couple of preservatives that might be considered, keeping in mind the high pH environment of cold process soap:

• Mild Preserved™ COS: This preservative works in a pH range of 2-8. While the high end of this range is 8, cold process soap typically has a pH higher than 8. It might offer some protection, but its full efficacy at the typical soap pH is not guaranteed.
• Coco-Preserve™: This is a natural preservative derived from coconut extract with a pH range of 4-8. Similar to Mild Preserved™ COS, its effectiveness might be limited at the higher pH of cold process soap.

Important Considerations for Cold Process Soap:

1. High pH: The naturally high pH of cold process soap provides some level of microbial inhibition. Some formulators choose not to use a preservative for this reason, especially if the soap is properly cured and stored.
2. Water Exposure: If the soap will be frequently exposed to water (e.g., left in a shower dish), adding a preservative can provide an extra layer of protection against microbial growth.
3. Additives: If you are adding ingredients like milks, purees, or botanicals, these can introduce microbes and may require a preservative for safety.
4. Challenge Testing: Regardless of the preservative chosen, it is highly recommended to perform a challenge test on your specific soap formula to ensure the preservative is effective at the final product's pH and against potential contaminants.

Given the pH limitations of most preservatives in cold process soap, some formulators rely on good manufacturing practices, proper curing, and packaging to ensure product safety. If you choose to use a preservative, select one with the highest possible effective pH range and always perform testing.