Techniques for globally approved skin testing

Without suitable instrumentation it is close to impossible to determine what a product is really doing for the skin. Those objective measurement methods and subjective evaluations are mutually dependent. No measurement can be performed without the subjective evaluation of the results by the user of such instrumentation. However, a pure subjective evaluation of the skin without appropriate measurement techniques is not able to achieve accurate results either. This relationship becomes clearer when looking for examples of skin colour measurements. Subjectively, the human brain cannot process slight changes in colour, especially when the colours are not viewed side by side, but at different points in time. Instrumental measurement however will clearly detect such slight changes. The achieved result must then be interpreted in context with the expected outcome or the hypothesis. For this, you will always need a knowledgeable and experienced person because ‘a fool with a tool is still a fool’, as the late Albert Kligman used to say. This relationship between objective measurement and subjective evaluation is not only true for the determination of differences in skin colour, but also for all other skin measurement parameters important for the cosmetic industry.

Skin measurements for claim support

About three decades ago, the first measurement methods were developed. Many of these techniques may seem crude nowadays. These first attempts of skin measurement were only used where they were developed and were available only to the respective company. Literature describes a variety of examples. The biggest disadvantages were that the measurements could not be compared and were not commercially available. Since then on an almost constant basis, new measuring techniques have been developed. Now, almost 30 years later, a wide variety of skin measuring equipment enables scientists to conduct all kinds of research and claim support. There is a multitude of skin measurement techniques available on the market for everyone. As many of the devices are easy to use and can be purchased with smaller budgets, these skin measurement techniques are affordable even for smalland medium-sized research institutions and cosmetic manufacturers, and are used to determine the effects of the product not only after its finalisation but also in all stages of its development. The most important functions to objectively measure are the skin barrier function, the stratum corneum water content (hydration), the surface pH-value, mechanical skin properties, skin colour and photo-protection (melanin and erythema), gloss, sebum excretion, epidermal and dermal thickness, temperature and thermoregulation, blood flow and microcirculation, surface morphology, and digital imaging. The development of further new techniques is constantly and quickly evolving. In addition to in vivo Raman spectroscopy, multiphotone tomography and ESR spectroscopy, new oscillating spectrographic methods can assess the penetration of products into the skin, or fluorescent laser scan microscopy serves to characterise further skin properties. Simple product claims that can be evaluated with skin measurement devices are for example the moisturising or the sebum regulation effect of a skin care product. These parameters can be easily and quickly assessed with the specific measurement devices like the Corneometer or the Sebumeter. Other claims are more sophisticated. The anti-ageing effect of a product can show in different parameters. Not only do these products often contain a sun protection factor, but they also usually have a hydrating effect. Many of them contain ingredients to decrease the wrinkle depth, they enhance skin firmness and elasticity, strengthen the barrier and even out the skin colour. For such products there are many different parameters that can be tested, from physical measurements to profilometric methods to evaluate the skin micro-and macro-structure. Also photographical documentation is often used to illustrate the anti-ageing effects of products and treatments.