Adding to Vitamin C Serum (CE Ferulic Type)

The base of this serum typically contains Vitamin C (L-ascorbic acid), Vitamin E (dl-alpha tocopherol), and Ferulic Acid.

Preservative

According to the staff's reply, the original formula you are using already includes a preservative. Therefore, you generally do not need to add an extra preservative. Adding more might exceed the recommended safe usage rate or cause instability.

If you intend to replace the existing preservative with a different one, you must follow the recommended usage rate for the specific preservative you choose. For example:

• PE 1090 Preservative: Typically used at 0.5% to 1.0%.
• Mild Preserved™ COS: Typically used at 0.75% to 1.5%.
• Caution: Be aware that some natural preservatives like NaturePreserve™ Ultra are not compatible with L-Ascorbic Acid and should not be used in this type of formula.

Always check the recommended usage rate for the specific preservative you are using and perform a challenge test to ensure effectiveness and safety.

Color

You can add water-soluble cosmetic colors directly to the serum. These colors are very concentrated, so you only need a tiny amount.

• Start by adding just 1-2 drops per 100g/ml of the serum.
• Mix well and check the color intensity.
• Add more drop by drop if needed until you achieve your desired shade.

Examples of suitable water-soluble colors include D&C Green No.5, FD&C Yellow No.6, or FD&C Red No.4.

Fragrance

You can use general perfume oils (fragrance oils) to scent the serum. However, since this is a facial product, it's best to use a low concentration to minimize the risk of skin irritation or sensitization.

• A typical usage rate for fragrance oil in a facial serum is 0.1% to 0.5% of the total formula weight.
• Start with a lower percentage (e.g., 0.1-0.2%) and add more gradually if you desire a stronger scent, but do not exceed the recommended maximum usage rate for the specific fragrance oil you are using.

Common fragrance oils like Strawberry Fragrance Oil, Jasmine Fragrance Oil, or Lavender Fragrance Oil can be used, but always consider potential skin sensitivity.