Understanding the Gas and Expansion in Your Scrub

The issue you're experiencing with your scrub expanding and pushing out of the container, along with the presence of gas bubbles, is most likely caused by microbial activity, specifically fermentation. This happens when microorganisms (like bacteria, yeast, or mold) grow in your product and consume certain ingredients, producing gas (often carbon dioxide) as a byproduct.

Let's address your questions:

1. Which ingredient causes the expansion or gas?
   The ingredients themselves don't directly cause the gas. Instead, certain ingredients act as food sources for microbes. In your formula, Coffee Extract and Honey are particularly prone to microbial growth and fermentation because they contain sugars and other nutrients. The gas is a result of these microbes breaking down these ingredients.
   As confirmed previously, Cetyl Alcohol does not cause gas.

2. Is the gas harmful if used, and does it affect shelf life?
   The gas itself (likely carbon dioxide) is not inherently harmful in this context. However, its presence is a clear indicator that your product is contaminated with microorganisms. Using a contaminated product can potentially cause skin irritation, infection, or allergic reactions, especially on compromised skin. More importantly, the contamination means the product is spoiled and its intended shelf life is significantly reduced or eliminated. The expansion and gas are signs that the product is no longer stable or safe for use.

3. Should any ingredients be changed?
   While you don't necessarily need to change the core ingredients like coffee extract or honey if they are essential to your scrub, you absolutely need to improve your preservation system. Phenoxyethanol alone, while effective against many bacteria, is often not sufficient to protect against yeast and mold, which are common culprits in fermenting natural ingredients like those in your formula.

   Recommendations:

   • Strengthen Preservation: Consider using a broad-spectrum preservative blend that is effective against bacteria, yeast, and mold. Products like Phenoxyethanol SA (eq. Optiphen Plus) are designed for broad protection and contain ingredients like Caprylyl Glycol and Sorbic Acid which enhance anti-fungal activity. Other broad-spectrum options containing combinations of preservatives might also be suitable.
   • Usage Rate and pH: Ensure the preservative is used at the correct recommended usage rate for your specific formula and that the pH of your final product is within the effective range for the preservative you choose.
   • Hygiene: Practice strict hygiene during manufacturing to minimize initial microbial contamination. Use sterilized equipment and work in a clean environment.
   • Challenge Testing: Ideally, perform a challenge test on your final formulation. This laboratory test evaluates the effectiveness of your preservative system against a range of microorganisms and is the best way to confirm that your product is adequately protected.

By improving your preservation system, you can prevent microbial growth, stop the gas production and expansion, and ensure the safety and stability of your scrub product.