28 TESTING
same time of day. It is also advisable to keep an untreated control area for comparison at all times.
Other factors influencing the skin are
subject-related. Many skin parameters are dependent on age, gender, the ethnic group and of course on the body site that is measured. Individual health and intake of medication may influence skin condition and functions, same as personal behavior and health consciousness, for example healthy nutrition versus junk food, smoking, alcohol, drinking (water), sleeping, excessive sunbathing etc.
Subject selection For meaningful results, you have to carefully choose your subjects. Ideally, you prepare a subject database that takes into account all subject-related information and can be filtered according to certain parameters to select subjects for different claims. You might also like to perform measurements on potential subjects in a pre-screening to judge their eligibility for the desired claim. You will not be able to prove anti-aging effects by measuring skin of a 25 year old subject. And it is almost impossible to improve the hydration of already well- moisturized skin. For moisturizing claims, you should instead rather measure on skin that is dry. The amount of subjects is also critical, the more, the merrier. In a pilot study to observe a trend, maybe twelve subjects are sufficient. For final product application studies, you should have at least 20 subjects.
Duration You should also consider how long the product will take to show an effect. For moisturizing claims, you will see an immediate increase of hydration after product application. Measuring the skin at certain time intervals, for example every hour can show how long this moisturizing effect will last. Always include an untreated control site. If you would like to prove that
Figure 5: The Visioscan® VC 20 plus – a real multi-
talented, economical device suitable for many different applications.
the product in the long term improves skin hydration, the subject has to use this product over a predetermined time, such as two to three weeks, and after this time needs to come back for skin measurement. On the follow-up measurement day, the product should not be applied. The same protocol could be applied for the measurement of TEWL or skin pH. Other effects, such as an improvement of skin elasticity or the depth of wrinkles without applying invasive surgery, will take longer to show. For such claims, the product has to be used for six to eight weeks to demonstrate its efficacy. You also have to develop a protocol for skin cleansing prior to the measurement. Especially sebum will take up to two to three hours to recover after the skin has been thoroughly cleansed. The cleansing process itself should be clearly defined, including the means and the timing of cleansing. At least 10 minutes prior to the
measurement, clothing needs to be removed from the measuring site. If you are interested in sebum measurement in areas hidden by clothing, the clothing should already be removed at the time of cleansing.
The amount of product and method of application should be defined in advance and for long-term use also clearly explained to the subject. After collecting all the results, the data should be evaluated in a meaningful and plausible way.
Figure 7: The cleansing procedure should be clearly defined.
PERSONAL CARE NORTH AMERICA
Conclusion To observe all these points might seem complicated at first glance. But once you have established a routine, you will see how easy these trials will become. And by testing and screening the efficacy of cosmetics in-house in all development stages of the product, you can be sure that the product that you hand over to a CRO for the final external documentation is the very best you can do.
PC
Figure 6: Pre-screening tests are important to find eligible subjects.
References 1 Fluhr JW. (Ed): Practical Aspects of Cosmetic
Testing – How to Set Up a Scientific Study in Skin Physiology, Springer 2011, ISBN: 978- 3642-05066-4
2 Pensé-Lheritier A-M. (Ed): Évaluation des produits cosmétiques – L’objectivation, Lavoisier, Paris, 2016, ISBN: 978-7430-2153-5
3 Berardesca E, Loden M, Serup J, Masson P, Monteiro Rodriguez L. The revised EEMCO guidance for the in vivo measurement of water in the skin, Skin Research & Technology 2018; 24: 351-358
4 Firooz A, Zartab H, Sadr B. et al. Daytime Changes of Skin Biophysical Characteristics: a study of Hydration, Transepidermal Water Loss, pH, sebum, Elasticity, Erythema and Color Index on Middle Eastern Skin, Indian Journal of Dermatology 2016; 61: 700, doi: 10.4103/0019-5154.193707
5 Matsui MS, Pelle E, Dong K, Pernodet N. Biological Rhythms in the Skin, International Journal of Molecular Sciences 2016; 17: 801,
6 Mehling A. Chronobiology and rhythms of the skin, Skin Care Forum
scf-online.com, Issue 40 – April 2006.
7 Le Fur I, Reinberg A, Lopez S, Morizot F, Mechkouri M, Tschachler E. Analysis of Circadian and Ultradian Rhythms of Skin surface Properties of Face and Forearm of Healthy Women, The Society of Investigative Dermatology 2001;117(3): September 2001.
Figure 8: Total security of the product properties through complementary in-house testing
March 2020
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