Developing a stable cosmetic product requires understanding and reacting to information gathered throughout the formulation process. To ensure a quality product is produced, the scientist must conduct various stability tests to identify issues that may arise. Although some issues may seem obvious, it is better to use the actual outcomes of several tests to form a proper formulation plan. Once a problem is identified, it is imperative to seek a solution to ensure long-term formulation stability. Having instabilities develop quicker will shorten the formulation time.
Troubleshooting most stability concerns in cosmetic formulations typically starts by looking at the raw materials in ingredient list. In skin care systems, the emulsification system, thickening ingredients, actives and emollients are usually examined. In a makeup formulation, structural items such as waxes and fillers are usually reviewed, as well as film-formers and colourants. Though modifying the ingredient composition can be considered, formulators need to first rule out any processing or raw material issues first. Adding a non-uniform thickener, for example, can cause an erratic low viscosity dial reading or formula splitting.
One of the most common and major problems a skin care formulator faces is formula separation or coalescence. There are many stability tests that can demonstrate this phenomenon. Emulsions are inherently thermodynamically unstable, so formulators must counteract this property with raw materials and processing. When an emulsion starts to break, the oil and water phase coalesces and separates. A thorough understanding of the theoretical factors influencing emulsion stability, as well as the various types of separation, is therefore important.
At the first sign of instability, the formulator should look for an efficient way to diagnose the problem and possibly accelerate it to replicate the tests while making improvements with modifications. A slight stability problem may necessitate less of a formula adjustment than would a complete split. Formulators must also account for the timing of the instability, and whether it happened in the first week or 10th week of the test, when adjusting their formula.
Although many industry standards serve as the basis for stability testing, some may not be helpful when quick adjustments are needed to stabilise a product and meet agreed upon launch dates. While the general parameters established for stability can pinpoint most issues, it can take up to three months to fully test a product and see instabilities. The focus here is using tools to quickly troubleshoot and gauge success, then correlate with traditional long-term stability.
Generally accepted approaches to predict the stability of cosmetics include measuring the product’s resistance to common stresses such as temperature extremes and exposure to light. Accelerated temperature testing is commonly used as a long-term stability predictor. Most companies conduct elevated temperature testing at 37°C (98°F) and 45°C (113°F). Products in elevated temperatures may exhibit separation, a decrease in viscosity or discolouration. The general consensus is that if a product passes stability at 45°C for 12 weeks, it should be stable at room temperature (RT) or on the market for up to two years.
Analysis of samples should include colour and odour evaluation, pH value, viscosity, texture and any signs of separation. Formulators should observe the product as it is taken out of the stability station. Applying the product after it has been through its testing parameter and seeing its flow and spreadability is also essential; in some instances, formulators may notice crystallizing or a slightly oilier pickup. These can be just the beginning of a larger problem and should be monitored. When conducting stability testing with light, different lighting conditions such as fluorescent and natural should be used.
Besides traditional stability tests, several others can provide the formulator with more immediate data. Quicker tests include rheological profile testing, differential scanning calorimetry (DSC) curves, microscopy and mechanical tests.
Cosmetic scientists depend on stability tests to maintain product consistency, and they desire the flexibility to modify testing protocols and familiarise themselves with various tools that provide long-term and real-time information. Specific tests may be developed to address new technologies or specific storage environments in certain markets.
Stability Testing Services, a division of Botanichem conducts stability testing for the cosmetics industry and can also help develop new formulations or assess existing formulations that are problematic. For more information contact Stability Testing Services.