Understanding Stability Testing

Understanding Stability Testing

Developing a stable cosmetic product requires understanding and reacting to information gathered throughout the formulation process. To ensure a quality product is produced, the formulator or cosmetic 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. 

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.

Here are some common issues to look out for:

Skin Care Separation or Coalescence

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.

At the first sign of instability, the formulator should look for an efficient way to assess the problem.

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 immediately or after a period of time.

General Stability Protocols

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 especially when the launch deadline is approaching.

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 laboratories 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 crystallising or a slightly oilier pickup. These can be just the beginning of a larger problem.

When conducting stability testing with light, different lighting conditions such as fluorescent and natural light should be used.

[Reference: www.cosmeticsandtoiletries.com]

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