Understanding Phenoxyethanol Concentration in Formulations

Thank you for your question regarding the use of Phenoxyethanol as a preservative. It's important to understand how concentration affects efficacy and safety, especially when developing products for a brand.

Concentration Calculation: Water Phase vs. Total Formula

Generally, preservatives like Phenoxyethanol are added to protect the water phase of a formulation, as microbial growth primarily occurs in water. Therefore, calculating the concentration based on the water phase is often a more accurate way to determine the effective preservative level in the environment where microbes thrive.

However, the regulatory limits and recommended usage rates for preservatives are typically given as a percentage of the total formula. For example, the maximum allowed concentration of Phenoxyethanol in cosmetics in many regions is 1% of the total weight of the final product. When formulating, you need to ensure that the amount of Phenoxyethanol added does not exceed this limit in the final product, regardless of how you calculate it during the development phase.

If you add 1% Phenoxyethanol based on the water phase, and the water phase is only a portion of the total formula (e.g., 50% water), the concentration in the total formula will be lower than 1% (e.g., 0.5%). Conversely, if you add 1% based on the total formula, the concentration in the water phase will be higher than 1% (unless the formula is 100% water). For regulatory compliance and general safety guidelines, the percentage of the total formula is the standard reference.

Recommended Usage Rate and Skin Irritation

The typical recommended usage rate for Phenoxyethanol is 0.5% to 1.0% of the total formula. Using 1% of the total formula is a common and often necessary concentration to provide adequate preservation against bacteria. However, as you noted, using higher concentrations can increase the risk of skin irritation, especially for individuals with sensitive skin. This is why the regulatory limit is set at 1%.

If you are concerned about irritation, you might consider:

• Using a lower concentration within the recommended range (e.g., 0.5% - 0.8%) if a challenge test proves it is still effective for your specific formula.
• Using a blend of preservatives that allows for a lower concentration of Phenoxyethanol while maintaining broad-spectrum efficacy. Products like Phenoxyethanol SA (eq. Optiphen Plus) or Chlorphenesin / Phenoxyethanol (Microcare PHC eq.) are examples of blends that offer broad-spectrum protection and may allow for lower overall Phenoxyethanol content or provide enhanced efficacy against fungi and yeast, which Phenoxyethanol alone is less effective against.
• Using a high-purity grade like Phenoxyethanol (Extra Pure), which is designed to reduce the risk of irritation associated with impurities.

Importance of Challenge Testing

For any product you intend to sell under a brand, it is crucial to perform a challenge test. This test involves intentionally contaminating your finished product formula with various microorganisms to see if the preservative system can prevent their growth over time. A challenge test is the only way to definitively know if the concentration and type of preservative you are using are effective for your specific formula composition and packaging.

Summary

While calculating based on the water phase can be useful during development, the standard and regulatory concentration is based on the total formula. The typical usage rate for Phenoxyethanol is 0.5-1.0% of the total formula. Using 1% is common for efficacy but may increase irritation risk compared to lower concentrations. Consider using blends or high-purity grades if irritation is a concern. Always perform a challenge test on your final formula before selling to ensure adequate preservation and product safety.

Products mentioned:

• Phenoxyethanol (Extra Pure)
• Phenoxyethanol SA (eq. Optiphen Plus)
• Chlorphenesin / Phenoxyethanol (Microcare PHC eq.)
• Phenoxyethanol P5