46 TRENDING TECHNOLOGIES
E. The skin is protected by this sebum with an extra lipophilic film. In other words, sebum has multiple beneficial functions that strengthen the skin barrier. It is an extra protection against the outside world by forming an additional physical barrier.
Thanks to the presence of vitamin E in the sebum, it also protects the stratum corneum and especially the skin lipids from destruction by free radicals. Sebum also has antimicrobial properties, especially against S. aureus. This bacterium is a fierce skin destructor. Finally, sebum together with the skin lipids
are crucial nutrients for the skin microbiota. The skin microbiota is in fact the microbial day cream for the skin with hydrating, antioxidant, antimicrobial and anti-ageing properties. The trio: stratum corneum, sebum and the
skin microbiota form an ingenious and efficient barrier that keeps out not just oil or water- soluble molecules, but also pathogens and free radicals.
This trio not only keeps the outside world out but also keeps the precious water inside the skin. Unfortunately, like the mighty mythological Achilles, the skin barrier has one weakness: surfactants.
The mechanism of surfactants Almost all naturally occurring molecules are either water-soluble or oil-soluble. Surfactants are the exception, as they are molecules with an oil-soluble part and a water-soluble part. The water-soluble part is in size far more superior compared to the oil-soluble part. Surfactants are the best-known solution to
clean a surface. As a matter of fact, it is the only known solution. Their oil-soluble part sticks into the dirt, as dirt is usually oil-soluble. The oil- soluble part of the most efficient surfactants is almost always made up of 10 (Decyl), 12 (Lauryl) to 14 (Myristyl) carbon atoms. Sometimes a surfactant is a mixture of 8, 10, 12, 14 (Cocoyl) carbon atoms. When the surfactant puts its oil-soluble tail
into the dirt, the surface of the dirt is completely covered with the water-soluble head. The dirt is now easily mixable with the water and is removed as shown in Figure 1.
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Figure 1: The cleaning mechanism of surfactants The main problem with surfactants is that
they are not selective. They cannot make a distinction between dirt and precious skin lipids. Therefore, surfactants not only remove the dirt on the skin surface but also the skin lipids between the corneocytes. The mortar of the wall is now washed away, and the barrier is lost. It takes the keratinocytes approximately three weeks to make and to arrange the skin lipids, while surfactants remove them in just a few seconds. Not only the skin lipids are washed away, but also sebum. This means that after washing the skin with surfactants, the skin is not protected anymore against pathogens, dirt and
free radicals. Also, water can now escape out of the skin. This latter is called transepidermal water loss (TEWL). Yet this is not the end of the problem. Now that sebum is gone, the skin microbiota lost an important source of nutrients. The skin microbiota is now like a powerful car without fuel.
The skin is cleaned to keep it hygienic, beautiful, and healthy but if the skin is washed regularly with surfactants, it will become dry, sensitive, flaky and red. So, surfactants are resulting in the opposite effect.
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The different surfactants When the skin is deprived of its lipids it feels very uncomfortable. Of course, not all the surfactants have the same impact on the skin lipids. A surfactant formulation such as a shampoo, shower gel or hand gel is usually composed of three types of ingredients. The first one is the primary surfactant.
866 556 241 SLES Lauryl glucoside Figure 2: The influence of different surfactants on the skin barrier (TEWL) PERSONAL CARE May 2024 CAPB SLS
These surfactants are anionic and are the main ingredient of the formulation. They remove efficiently dirt and of course also skin lipids. They are also responsible for foam. Typical examples of primary surfactants are sodium laureth sulfate (SLES), sodium lauryl sulfate (SLS) or sodium cocoyl sulfate. The second type of ingredient is the
secondary surfactant. These surfactants are amphoteric. When primary surfactants were used alone, the formulation would feel quite harsh and would also make the hair unmanageable. Secondary surfactants mask the harshness of the primary surfactant. They also boost the foam. The most famous example of a secondary
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(TEWL Increase %)
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