Formulation Questions Answered

Let's address your questions regarding your proposed formulation:

1. Can this formula be made without an emulsifier?
   No, a formula containing both a significant oil phase (60%) and a water phase (39.5%) cannot form a stable, homogenous mixture without an emulsifier. Oil and water are immiscible and will separate into layers over time. Emulsifiers are necessary to create and maintain an emulsion (like a cream or lotion) where oil and water are blended together.

2. If the oils don't mix completely, can it still be used by shaking?
   Yes, if you choose not to use an emulsifier, the formula will separate. You can still use it by shaking well before each use to temporarily disperse the oil phase within the water phase. This type of product is known as a biphasic system (like some serums or makeup removers) and requires shaking before application.

3. If SkinLipid™ is used in the oil phase without an emulsifier, will the formula mix, considering SkinLipid™ might solidify at room temperature?
   SkinLipid™ is designed to integrate into the skin's lipid barrier and has some amphiphilic properties, but it is not a traditional emulsifier capable of creating a stable emulsion with a high oil load (60%) in a water base. Therefore, the formula will still separate without a proper emulsifier. Regarding its solidification, SkinLipid™ is a flake powder that dissolves in oil with heat. While it forms a lamellar gel structure, if it solidifies within your oil phase at room temperature, it could make it difficult to shake and mix the product effectively before use. You might need to gently warm the product to ensure the oil phase is liquid and can be dispersed.

4. Can Glycerin cause skin irritation in large amounts? What is the recommended usage percentage for maximum benefit?
   Glycerin is a very common and generally gentle humectant. While it can be used at high concentrations (up to 100% in some applications, though not recommended directly on skin), using it in very high percentages in a cosmetic formula can lead to a sticky or tacky feeling on the skin. For optimal humectant benefits in a leave-on product without excessive stickiness, a usage rate typically between 5% and 20% is often recommended. The ideal percentage depends on the overall formula and desired skin feel.

5. Any other recommendations?
   Since you want to avoid emulsifiers due to potential irritation, consider formulating either a purely oil-based product (like a facial oil or cleansing oil) or a purely water-based product (like a serum or toner) if possible, depending on your desired outcome. If you need to incorporate a small amount of oil-soluble ingredients into a water base, using a solubilizer might be an option, though solubilizers can sometimes also cause irritation depending on the type and concentration. Always perform stability testing (physical and microbial) on your final formulation to ensure it is safe and remains consistent over time, especially with natural extracts and a water phase.