Color Tone. Our laboratory has studied hair color steadfastness by utilizing hair tresses and analytical chemistry. Briefly, hair tresses are treated with hair dye according to the manufacturer's guidelines. Then over the course of 5 days of treatment, the tresses are gently shampooed with various water conditions, taking into account water hardness, temperature, and so on, at 10 minute intervals.
Aliquots of the washings are then subjected to standard spectrophotometry scanning to evaluate changes in baseline and in treated color hair tone. This approach can also be used when one is comparing current products with market innovators to perform simple pilot screening studies in developing claims for parity or superiority. The data generated from these pilot studies can then in turn be used to develop definitive clinical studies for ultimate marketing claims.
Penetration Studies. Further, to evaluate ingredient penetration into the hair shaft or even deeper into the hair unit (cuticle), hair tresses again can become
a valuable testing tool. One can simply radiolabel the hair care preparation with something such as tritiated thymidine or carbon-14. Tritium is a low beta emitter, and with relatively simple radiation safety precautions one can generate some eloquent autoradiograph clearly demonstrating the penetration of various chemical entities into the hair shaft and deeper for "hair nutrient claims." Again, one can perform the testing over a 5-day time period for 10 minutes per treatment to establish the kinetics for ingredient penetration .
For those studies, where working with radioactive isotopes is simply not an option, one can look to specific fluorescein probes, coupled with fluorescent epimicroscopy, to track ingredient penetration. Although such techniques clearly are not as quantitative and precise as the radiolabeled approach, one can generate some compelling data in comparison to appropriate controls. One of the downsides of this experimental approach is that fluorescein can nonspecifically stain keratin molecules, thereby producing at times a significant amount of nonspecific "noise." However, with some simple trial-and-error sequences using various concentration and ratios of product to the fluorescein dye, one can derive some very striking photography claims .
If one uses double labeling such as fluorescein isothiocyanate (green) and phycoerythrin (red) in testing one hair care product against another, one could conduct a clinical study again taking hair samples every day over the course of 5 days of treatment. Typically one would use a regimen of hair products with a cleansing shampoo, conditioner, and even a hairstyling product. However, by using double-labeling fluorescent microscopy techniques, it becomes possible to confirm that the penetration observed is indeed due to penetration of the product ingredient into the hair shaft, not an artifact of fluorescein chemistry. From a marketing perspective, moreover, these fluorescent probes can indeed provide a high-impact, visually compelling color photography for a variety of multifunctional hair care products.
There are many other requirements for claims support related to multifunctional products including deposition of active ingredients, hair strength, and elasticity. These are commonly used in the industry and are discussed elsewhere.
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