With the Speed of Light: A Look at Accelerated Testing

October 9, 2007 | Contact Author | By: Johann Wiechers
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Whereas most people know that scientists like Copernicus unveiled that the world is spinning at a constant speed— a logical consequence of placing the sun at the center of the universe— most feel that the world is turning at an ever increasing speed. Almost 20 years ago, people sent contracts by mail and subsequently waited a few days if not weeks until the other party had received, read, signed and returned them. Nowadays, we take a former contract, change a few words, print it off, sign it, scan it in, attach it to an e-mail, enter an e-mail address and hit the send button. And often, it is annoying if a response is not received within a few hours.

Increasing the speed of something is a relative thing. In times gone by, on August 12, 490 BC to be precise, a messenger was sent out from Marathon to Athens to inform the Athenians that the Persians were coming. Pheidippides ran the 42 km distance without stopping. He would have been subjected to temperatures as high as 39 °C, and just after he arrived in Athens with the news, he died most likely from heat stroke.

The world wants instantaneous responses. When things can go faster, it is hard to accept a slower than maximum speed. Comsumers in the personal care industry often face a temporary benefit, but when that benefit becomes standard, they want more, i.e. darker skin tan, less skin tone, faster delivery, leaner thighs, longer legs or holidays, etc., etc. Where is this list of superlatives leading you...to my topic—accelerated testing.

We test a number of things in our cosmetic industry. We test for safety, actually, the in vitro alternatives will discuss next time have a much greater chance of being accepted if they also offer a speed benefit; for stability; for efficacy; for microbiological contamination; and for interactions between the (ingredients of the) product and its container. Physical stability testing specifically can be quite time-consuming. Imagine you had to store all your samples for three years before you were able to state that your product was stable for this period of time. This would be far too long relative to the lifetime of the product in the market place.

Our world would have moved on. We, therefore, invented accelerated testing to gain time. Take physical stability testing of formulations as an example. Emulsions may undergo flocculation (internal droplets form a weak, reversible association without a change in size), coalescence (merging of internal phase droplet to form one larger particle – but of different sizes), Oswald ripening (the newly formed larger droplets are uniform in size), creaming or sedimentation (less dense particles rise to the top), or phase inversion.

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....

—Johann W. Wiechers, PhD
Technical Advisor, Allured Publishing Corp. 
Independent Consultant for Cosmetic Science, JW Solutions