Adjusting Formulation Percentages When Adding Ingredients

Asked by: krittikakai On: March 29, 2015 Product Type: Cosmetics

Question

When adding new ingredients to an existing cream or lotion formula, how should the percentages of the original ingredients be adjusted to maintain a total of 100%? For example, in a sunscreen formula with 77.5% Distilled water, 20% SPF Protect Ultra, 1.5% Light cream maker, and 1% Phenoxyethanol, if I want to add Humectant (3%), Whitening Agent (2%), Antioxidant (1%), and Colorant (0.5%), how do I calculate the new percentages, especially for the water component? And how do I convert these percentages to grams for a specific batch size (e.g., 100g or 500g)?

Answer

Adjusting Formulation Percentages

Yes, when you add new ingredients to an existing formula, you must adjust the percentages of the other ingredients so that the total percentage remains 100%.

The general method is to reduce the percentage of the base ingredient (often water in creams and lotions) to make space for the new ingredients.

Example using your sunscreen formula:

Original Formula:

  • Distilled water: 77.5%
  • SPF Protect Ultra: 20%
  • Light cream maker: 1.5%
  • Phenoxyethanol: 1%
  • Total: 100%

Suppose you want to add:

  • Humectant: 3%
  • Whitening Agent: 2%
  • Antioxidant: 1%
  • Colorant: 0.5%
  • Total of new ingredients: 6.5%

To keep the total at 100%, you need to reduce the existing ingredients by 6.5%. The easiest way is to reduce the water:

New Water Percentage = Original Water Percentage - Total Percentage of New Ingredients
New Water Percentage = 77.5% - 6.5% = 71%

The adjusted formula would be:

  • Distilled water: 71%
  • SPF Protect Ultra: 20%
  • Light cream maker: 1.5%
  • Phenoxyethanol: 1%
  • Humectant: 3%
  • Whitening Agent: 2%
  • Antioxidant: 1%
  • Colorant: 0.5%
  • Total: 100%

Calculating in Grams:

Once you have the percentages, you can calculate the amount in grams for any batch size. For a 100-gram batch, the percentages are equal to grams (e.g., 71% water is 71 grams). For a 500-gram batch, you multiply the total batch size by the percentage (as a decimal): 500 grams * 0.71 = 355 grams of water.

Important Notes:

  • The specific percentage for each new ingredient depends on its recommended usage rate and desired effect.
  • Always consider ingredient compatibility and the stability of the final product when modifying a formula.

Tags

Cream Formulation Adjustment Ingredient Addition Ingredient Ratio Sunscreen Formulation