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With the Speed of Light: A Look at Accelerated Testing
Posted: October 9, 2007
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How do we do our accelerated testing of emulsions? We are aware of freeze-thaw cycles, prolonged testing at elevated temperatures, but are they truly predictive? For example, by subjecting a formulation to high temperatures, the assumption is made that if a formulation is stable after 3 months at 50°C, it would be stable for 2 years at ambient temperatures. The problem with this approach is a possible phase change that may occur at the formulation’s critical temperature or breakdown, that may not occur at ambient temperatures for several years.
Centrifugation tests can also be misleading, since subjecting the formulation to a high gravity force may cause coalescence that may not occur at normal gravity forces. So, how valid are these accelerated tests? Do they depend on the formula? Do they depend on the product? Help is definitely needed here, and I thought I had that help when I found Guidelines on Stability Testing of Cosmetic Products, a document compiled by the CTFA and Colipa in March 2004. Unfortunately, after review of the document, the reader knows just as much (or little) as before reading this document.
The document states, “There is very little generally-applicable published research to support specific accelerated methods for predicting cosmetic shelf life.” Had we not already reached that conclusion? It also states, “Accelerated test conditions are internationally recognized as appropriately predicting product shelf life in many industries,” and continues to list a number of parameters that need to be investigated including temperature variations and extremes, mechanical and physical tests and light stability. Did we not just conclude that these tests were inappropriate under certain conditions? Luckily, the document does leave enough space for new experimentation appropriate for the product form. It states, “Each manufacturer should design their stability testing program such that it is reasonable and efficiently addresses the testing required.” While, on the one hand, this is pretty useless, it means on the other hand that you may design your own testing regimen, provided it is reasonable and efficiently addresses the testing required. Notice a resemblance with what is written about cosmetic claim substantiation in the European law?
Claims should be supported by sound, relevant and clear evidence based on generally accepted data, experimental studies (instrumental/biochemical methods, sensory evaluations, studies without using human subjects) and consumer evaluations. Here the big question is always, what is sound and what is relevant? For accelerated testing, what is reasonable and what is efficiently enough?
Anyway, accelerated testing is something where you can almost do whatever you want. If you do it badly and your product that you declared to be stable is in reality unstable, you are the one that will suffer in the market place. And who cares about a three-years stability certificate if we launch new “improved” formulations every six months anyway? Would it not be better if our products would spontaneously degrade as soon as another improved version gets onto the market? You may think it is crazy, but that is what happens in the computer industry. I will have to save this Word document, written on my new Vista computer, in the Word 2003 format, as otherwise my friends at Allured may not be able to open it. And that is, like it or not, normal. Something works till something better comes along. Fax machines replaced the registered mail. E-mails replaced fax machines. The faster option becomes the norm until we reach the speed of light. What happens then is all very relative....