Chapter 2 - Essential Formulation Techniques
Incorporating Active Ingredients into Emulsions: Tips for Stability and Efficacy
Introduction
Active ingredients—such as vitamins, acids, and antioxidants—are the key players in skincare formulations that deliver targeted benefits, from anti-aging to brightening and exfoliation. However, adding these powerful actives into emulsions requires careful consideration to ensure stability and efficacy. In this post, we’ll explore how to incorporate active ingredients into emulsified products like lotions and creams, covering best practices for stability, pH compatibility, and maximizing effectiveness.
Why Active Ingredients Need Special Attention in Emulsions
Active ingredients can be sensitive to factors like pH, temperature, and oxidation. Without proper handling, they can destabilize the emulsion, lose effectiveness, or even irritate the skin. By carefully considering each active ingredient’s needs, you can create stable, high-performing emulsions that deliver their intended benefits.
Key Considerations for Adding Actives to Emulsions
1. pH Compatibility
Every active ingredient has an optimal pH range where it remains stable and effective. Adding it to an emulsion with an incompatible pH can lead to degradation or irritation.
Examples:
Vitamin C (L-Ascorbic Acid): Needs a pH below 3.5 to remain stable and effective.
Niacinamide: Stable between pH 5-7. Using it in more acidic formulations can cause it to break down into niacin, leading to potential irritation.
AHAs (Glycolic, Lactic Acid): Effective at a pH of 3-4 for exfoliation benefits.
2. Temperature Sensitivity
High temperatures can degrade certain actives, particularly antioxidants, peptides, and vitamins. For emulsions, it’s best to add these ingredients in the cool-down phase, once the temperature drops below 40°C.
Examples:
Vitamin E (Tocopherol): Best added below 40°C to prevent oxidation.
Peptides: Heat-sensitive and should be added in the cool-down phase to maintain their structure and activity.
3. Solubility
Actives are either oil-soluble or water-soluble, and their solubility determines which phase they should be added to in the emulsion.
Oil-Soluble Actives: Retinoids, Coenzyme Q10, and Vitamin E are added to the oil phase.
Water-Soluble Actives: Niacinamide, hyaluronic acid, and AHAs are added to the water phase.
Note: Proper solubilization is crucial to avoid clumping or separating. For some actives, pre-dissolving them in a small amount of compatible solvent can help with even distribution.
4. Concentration Limits
Actives must be used within safe and effective concentration ranges. Going over recommended percentages can lead to irritation, while using too little may reduce efficacy.
Examples:
Retinol: Typically used at 0.1-1% in most skincare formulations.
Niacinamide: Effective at 2-5%, with minimal irritation risk.
Glycolic Acid: For at-home products, 5-10% is common, as higher concentrations increase the risk of irritation.
5. Interaction with Other Ingredients
Some actives are incompatible with each other and can cause irritation or reduced effectiveness when combined.
Examples:
Vitamin C and Niacinamide: Historically thought to be incompatible, recent studies show they can coexist, but it’s best to monitor pH.
Retinol and AHAs/BHAs: Combining strong exfoliants and retinoids can increase irritation, so they are often used in separate products.
Step-by-Step Guide to Incorporating Actives into Emulsions
Here’s a step-by-step guide to safely incorporate active ingredients into an emulsion:
1. Select Your Actives Based on Product Goals
Determine which actives will best achieve your formulation’s purpose, whether it’s brightening, moisturizing, anti-aging, or exfoliation.
Research each active’s ideal pH range, concentration, and solubility to ensure it aligns with the product type and other ingredients.
2. Formulate with pH-Dependent Actives in Mind
Adjust the pH of the emulsion to match the needs of pH-sensitive actives. For example, if formulating an AHA-based cream, set the emulsion’s pH to around 3-4 to ensure the AHA remains effective.
Tip: Always test pH after adding actives and adjust as necessary with pH modifiers, like citric acid to lower pH or sodium hydroxide to raise it.
3. Pre-Dissolve Actives When Needed
Some actives, like salicylic acid (BHA), are difficult to dissolve directly in an emulsion. Pre-dissolving them in a small amount of a compatible solvent, like propanediol, can help with even incorporation.
Tip: Use only as much solvent as needed to dissolve the active fully, as adding too much can alter the emulsion’s balance.
4. Add Heat-Sensitive Actives During the Cool-Down Phase
After emulsifying and mixing the oil and water phases, allow the mixture to cool to below 40°C. Then, add heat-sensitive actives, such as peptides, Vitamin C derivatives, or antioxidants.
Tip: Mix gently after adding these actives, as excessive stirring at this stage can destabilize the emulsion.
5. Test for Stability and Adjust if Necessary
Check the final product’s stability through stability testing. Look for any signs of separation, pH drift, or changes in texture over time.
Test pH again after adding all actives to confirm that it remains within the target range. Adjust if needed to ensure both stability and compatibility with the active ingredients.
Sample Emulsion Formulations with Active Ingredients
1. Anti-Aging Cream with Retinol and Vitamin E
Water Phase:
Distilled Water: 60%
Glycerin (Humectant): 3%
Oil Phase:
Jojoba Oil (Emollient): 10%
Glyceryl Stearate (Emulsifier): 4%
Cetearyl Alcohol (Thickener): 2%
Cool-Down Phase:
Retinol (Active, oil-soluble): 0.5%
Vitamin E (Antioxidant): 0.5%
Preservative: 0.5%
Process: Heat water and oil phases to 70°C, blend them, and allow to cool. Add retinol, Vitamin E, and preservative below 40°C to ensure stability.
2. Brightening Lotion with Niacinamide and Hyaluronic Acid
Water Phase:
Distilled Water: 65%
Hyaluronic Acid Solution (1%): 5%
Niacinamide (Active): 5%
Oil Phase:
Caprylic/Capric Triglyceride (Emollient): 8%
Polysorbate-20 (Emulsifier): 2%
Cool-Down Phase:
Panthenol (Pro-Vitamin B5, Active): 2%
Preservative: 0.5%
Process: Heat water and oil phases, blend them at 70°C, and allow to cool. Add panthenol and preservative at below 40°C to maintain the efficacy of the actives.
Testing Stability of Emulsions with Actives
Stability testing is essential to ensure that active ingredients remain stable and effective within the emulsion. Here are recommended tests to conduct:
Temperature Stability Test: Store samples at different temperatures, such as room temperature, 40°C, and refrigeration, and observe for separation, pH drift, or changes in color or texture.
Freeze-Thaw Cycles: Freeze and thaw the emulsion three to five times to simulate temperature stress and test for separation.
pH Monitoring: Track pH over time to check for any shifts, particularly for pH-sensitive actives like AHAs and Vitamin C. Consistent pH helps ensure active stability and effectiveness.
Troubleshooting Common Issues with Actives in Emulsions
1. Separation of Actives in the Emulsion
Solution: Increase the emulsifier concentration or choose an emulsifier better suited to the oil or water content.
Tip: For some active ingredients, adding a secondary emulsifier or stabilizer can help keep the emulsion intact.
2. pH Drift Affecting Active Efficacy
Solution: Use a buffer system or pH stabilizer to help maintain the desired pH over time.
Tip: Ingredients like sodium citrate can help maintain a stable pH, especially in acidic emulsions with AHAs.
3. Degradation of Heat-Sensitive Actives
Solution: Ensure that all heat-sensitive actives are added in the cool-down phase and avoid reheating the emulsion after they are added.
Tip: For highly sensitive actives like peptides, consider airless packaging to reduce oxygen exposure.
Key Takeaways
pH Compatibility: Choose actives that align with the emulsion’s pH, and test pH after adding each active to avoid irritation or reduced efficacy.
Temperature Control: Add heat-sensitive ingredients during the cool-down phase to maintain stability and effectiveness.
Stability Testing: Conduct stability testing on emulsions with actives to check for separation, pH drift, and texture changes over time.
Final Thoughts
Incorporating active ingredients into emulsions requires careful planning, but with the right techniques, you can create effective, stable products. By mastering pH compatibility, solubility, and stability testing, you’ll be able to formulate high-performance emulsions that meet consumers’ needs. In our next post, we’ll dive into sustainable and eco-friendly practices in formulation, including how to create waterless skincare products and select environmentally friendly ingredients.
Stay tuned!