DIY Cream Base Formulation: Ingredient Amounts and Preservative Selection (Phenoxyethanol)

Hello! I understand you're working on a DIY cream base and need guidance on ingredient amounts, especially preservatives.

Building upon the staff's previous advice regarding the key thickening agents and total oil content, here is some additional information on other ingredients and your question about preservatives:

Regarding Preservatives:

• The original formula uses a blend of preservatives (Diazolidinyl Urea, Phenoxyethanol, Methylparaben, Propylparaben). Using a combination like this is intended to provide broad-spectrum protection against bacteria, yeast, and mold.
• You mentioned you only have Phenoxyethanol. Phenoxyethanol is primarily effective against bacteria but may not provide sufficient protection against yeast and mold when used alone.
• The typical usage rate for Phenoxyethanol in cosmetics is generally 0.5 - 1%.
• Important Note: Using only Phenoxyethanol at its typical rate in a complex formula with a high water content might make the product more susceptible to microbial contamination compared to the original formula's broad-spectrum blend. If long-term product safety is a concern, it's highly recommended to consider sourcing a broad-spectrum preservative blend suitable for creams, or using one in addition to Phenoxyethanol.

Amounts for Other Ingredients:

• Water (aqua): This will be the balance of the formula after adding all other ingredients.
• Oils (Jojoba, Sesame, Almond, Avocado, Dimethicone): As per the staff's advice, the total oil content should not exceed 30%. The exact percentage depends on the desired skin feel (higher oil content results in a richer, more occlusive feel). A total oil phase of around 10-20% is common for a basic cream base.
• Thickeners/Emulsifiers (Cetyl Alcohol, Glyceryl Stearate, PEG-100 Stearate, Stearyl Alcohol, Polysorbate 20):
  • Cetyl Alcohol and Stearyl Alcohol are fatty alcohols that help thicken the cream and provide emollience. Use around 1-5% each.
  • Glyceryl Stearate and PEG-100 Stearate are often used together as an emulsifying system to bind the water and oil phases. Use around 3-7% for this blend.
  • Polysorbate 20 can act as a co-emulsifier or solubilizer. Use around 0.5-3%.
• Humectants/Slip Agents (Sorbitol, Butylene Glycol, Sodium Hyaluronate):
  • Sorbitol and Butylene Glycol are humectants that draw water to the skin and improve texture. Use around 1-5% each.
  • Sodium Hyaluronate is an excellent humectant and skin conditioner. Use around 0.1-1% (higher concentrations are very viscous).
• Thickener (Carbomer): A water-phase gelling agent. Use around 0.1-0.5%. It requires neutralization with Triethanolamine to form a gel.
• pH Adjusters (Citric Acid, Triethanolamine): Used to adjust the final pH of the cream to a skin-compatible range (typically 5.5 - 6.5).
  • Triethanolamine is used to neutralize Carbomer and raise pH.
  • Citric Acid is used to lower pH.
  • The amount needed depends on the other ingredients; you'll need to add gradually and measure the pH until the desired range is reached.

In Summary:

DIY cosmetic formulation requires understanding ingredient functions and often involves experimentation to achieve the desired texture and performance. The percentages provided here are typical starting ranges. You can begin with values within these ranges and adjust in future batches based on your results.

Crucially, regarding the preservative system, using only Phenoxyethanol at 0.5-1% might limit the product's shelf life and microbial stability compared to a broad-spectrum blend. Storing the finished product in a cool place can help extend its life.

I hope this information is helpful! Feel free to ask if you have more questions.