Oil Percentage in Serum

The appropriate percentage of oil to use when formulating a serum with oil in water depends on two main factors:

1. Suitability/User Preference: This is subjective and depends on the user's skin type, climate, and preference.

   • For slightly dry skin or normal conditions, starting with 5-10% oil is recommended.
   • For very dry skin, cold climates, or constant exposure to air conditioning, a higher percentage might be preferred as it helps prevent water loss from the skin.

2. Technical Limitations (Emulsifier): The maximum amount of oil you can incorporate depends heavily on the emulsifier used.

   • Some emulsifiers, like Light Cream Maker, can handle a high oil load (40%+).
   • If using Glyceryl Stearate / Cetyl Alcohol, it can typically handle 20-25% oil, although this can vary depending on the specific type of oil used. For more precise calculations, studying HLB values is recommended.

Using Glyceryl Stearate as an Emulsifier

Regarding the mixing process when using Glyceryl Stearate:

• You must mix the emulsifier with the oil phase while it is hot. Do not wait for it to cool down.
• After melting the Glyceryl Stearate and mixing it into the oil phase, it's important to maintain the heat for about 5-10 minutes to ensure complete and stable emulsification.
• Be mindful of the temperature; try not to exceed 70°C to avoid degrading heat-sensitive ingredients. Prolonged heating should also be avoided.