Uncovering Stability Issues: The Obvious and Not So Obvious

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 the problem is identified, it is prudent to find a quick manner to assess progress and ensure long-term formulation stability to guarantee success; and having instabilities develop quicker will shorten the formulation time.

While it may seem that formula stability would have the same meaning to most of the cosmetic industry, it can vary from company to company. In a recent European conference, consumer attendees were asked, “What would you consider a stable personal care product?” The most common answer was a product that would not be compromised if left in a hot car for a period of time. Although this answer may seem extreme and “less scientific” to some, it exemplifies the high expectations that consumers have, which cosmetic scientists must strive to accomplish. After all, the interior of a car can quickly become as high as 140°F (60°C) in approximately 90 min on a hot, sunny day.1

Troubleshooting most stability concerns in cosmetic formulations typically starts at the usual raw material classes comprising the skin care and makeup 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 colorants. Though modifying the ingredient composition must be considered, formulators should 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.

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