Proving cosmetic claims of microbiome products


Bacterial analysis can be very useful to measure the effect of antibacterial washes, presumably showing a reduction of the bacteria on the skin. Also, the amount of specific bacteria species present is interesting for studying the effect of antiacne or antibiotic products. It remains in any case difficult to compare the full scope of microbial compositions of different individuals. Therefore, many cleansing claims are proven by traditional methods focusing on defined species of bacteria.


For cosmetic care products, bacterial analysis might show if the bacteria of probiotic products or the nutrition for special bacterial species in prebiotic formulations will lead to a shift in the microbiome composition. It will however yield very little information if a product with a microbiome claim will improve the skin condition. 


For skin health claims, despite of all microbiome research, we still need to revert to the traditional methods of skin testing. 


Assessment of the skin barrier by transepidermal waterloss (TEWL) measurement


The skin works as a barrier between our inner body and the environment. The measurement of the emission of water through the skin into the environment, the so-called transepidermal waterloss (TEWL), is one of the most-used methods to assess the skin barrier quality.16 The skin protects the inner body from losing a huge amount of water by evaporation. Healthy skin at most skin sites shows at ideal ambient conditions of 20-22°C with a relative ambient humidity between 40-60% a TEWL between 7-15 g/h/m2.  If the barrier is damaged, a higher loss of water will be measured. The Tewameter® with its open measurement chamber is the most-used probe for this kind of measurement. 


Studying repair effect of products by TEWL measurements


The TEWL measurement can also be used to assess the barrier repairing or protecting effect of products. The skin is artificially damaged by creating small wounds or by standardised tape stripping, often using Corneofix® or Desquame®. The damage will show in an increased TEWL and can be evaluated as well as the time the skin takes to recover to healthy TEWL values.17 


Measurement of the skin surface hydration


Healthy skin should have a higher surface water content, not wet, but by no means dry. Together with the skin lipids (sebum) present and cell aggregates from the desquamation process, the water forms an emulsion called the hydrolipic film that covers the skin surface, protecting it and keeping it supple. 


The water content of the hydrolipidic film is related to the water binding faculty within the upmost skin layers of the stratum corneum. The deeper you dive into the stratum corneum, the higher the water content. The upper layers of the stratum corneum contain less water and are most susceptive to the effects of moisturising products.18 Therefore, the measurement of these outer skin layers is very important for the assessment of skin health and the hydrating influence of applied products. 


The moisture measurement should be done swiftly, preventing the collection of water from the TEWL between the skin surface and the measurement contact area (occlusion). The Corneometer® is the world’s most-used instrument to determine stratum corneum hydration in the most important upper layers by capacitance. The moisture measurement with the Corneometer takes less than one second. The result is immediately displayed in arbitrary units and can be interpreted and compared. Also the L’Oréal Skinchip® or the MoistureMap® device are based on capacitance measurement. They display the distribution of the water on the contact site by imaging the capacitance readings. Other techniques of assessing the water content of the skin that have been applied are impedance measurement, evaluation of scaliness and desquamation, infra-red measurement or Raman spectroscopy. 


Sebum content


The Cambridge Dictionary describes the lipids excreted by the sebaceous glands as “an oil-like substance produced by the sebaceous glands in the skin that makes hair shiny and prevents skin from becoming dry”.19 The role of sebum in atopic dermatitis has been dismissed by different investigations in the past. More recent studies however, have shown that in diseased skin conditions such as atopic dermatitis, sebum levels are considerably lower than in healthy individuals.20 On the other hand, increased sebum production is correlated to the occurrence of acne.21 In ophthalmology, a reduction of lipids produced by the meibomian glands is linked to dry eye indication.22 The amount of lipids on skin, hair and also in the tear film according to these findings will also offer information on their health state. 


Sebum is very different at different skin areas. In the face and on the scalp sebum levels are highest.23 Other skin sites show much lower values. The Sebumeter® is the standard device to measure the sebum secretion on the skin surface. The special matte tape will become transparent by absorbing sebum present on the skin surface. The transparency will be measured; the more transparent, the higher the sebum level. Other methods like Sebufix® or Sebutape® use special microporous tapes that show the sebum pits on the skin surface as dark blotches of different sizes. These blotches can be evaluated according to their portion of the measurement area, their sizes and numbers. 



source from https://www.personalcaremagazine.com