72 TESTING
In vitro testing - not just for product claims
Ana Carolina Kelmer, Georg Wiora, Christiane Uhl, Diana Khazaka – Courage + Khazaka
The importance of in vitro tests for analysing the skin and its functions has increased continuously in recent years. Cultured skin models and skin-like tissue mimicking the characteristics and functions of human skin are readily available and provide a controlled basis for numerous analyses, allowing researchers to manipulate variables more precisely. Notwithstanding the complex interactions
between a living body and the environment, they also offer the advantage that tests will score rather reproducible results. This enables the study of specific factors such as environmental influences or genetics on the skin. In particular for cosmetic and dermatological research, in vitro tests offer many advantages. Not only do in vitro measurements provide
precise insights into the dermal absorption of substances, crucial for assessing the safety of cosmetics, pharmaceuticals and other products. Time and financial aspects also play an important role: in vitro tests offer a cost-efficient and time-saving alternative to costly in vivo studies. Studies on humans are expensive; subjects
need to be recruited and often need to be available for several appointments. The versatility of in vitro tests also allows scientists to explore variations in skin thickness, and how they affect the penetration and efficacy of skin care ingredients. This information is vital for adapting products to different skin types and conditions.
Ethical concerns Another driving factor is the ethical aspect. The use of animals for testing chemical substances is increasingly being criticised, and in vitro tests offer an ethically acceptable alternative for generating meaningful data. Also, the efficiency of animal tests is disputed, since biological structures and processes of animals and humans cannot always be compared with each other. In the European Union, animal testing of
cosmetics or chemical substances that are manufactured exclusively for use in cosmetic products is prohibited. According to the European Cosmetics Regulation (Regulation (EC) No. 1223/2009),1
cosmetics whose
ingredients were tested on animals after this date may no longer be officially sold in the EU since March 2013. Many other countries have issued similar regulations. The growing
PERSONAL CARE April 2024
Figure 1: In vitro tests of cosmetic products gain more and more importance
awareness of animal welfare and the ban on animal testing have further cemented the acceptance and integration of in vitro methods.
Logistical challenges Last but not least, experience from the Covid-19 pandemic has made it clear that measurements on humans can not only be unhygienic, but also pose logistical challenges. Due to the risk of infection of subjects and personnel, and also due to staff shortages, in many laboratories, measurements on humans had to be suspended
for considerable periods of time. In vitro measurements have become
increasingly important as they represent a safe and reliable alternative for obtaining meaningful data without jeopardising the health and safety of staff and the test subjects. Conducting experiments on skin cultures
facilitates multi-sample screening, enabling tests of multiple substances or conditions simultaneously. The incorporation of in vitro approaches as recognised methods for assessing skin tolerance and other parameters in numerous guidelines and regulations also emphasises the increasing relevance of these test methods. Organizations such as the ECVAM (European
Centre for the Validation of Alternatives Methods), the OECD (Organisation for Economic Co-operation and Development) and the COLIPA (European Cosmetic Toiletry and Perfumery Industry Association) have validated many of these tests.2-5
Common in vitro measurements Common in vitro measurements on skin cultures include the following ■ Permeation studies: Investigating the penetration of substances through the skin layers. ■ Assessment of inflammation and immune responses: Studying the skin’s response to
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