TESTING 43
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®
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
April 2019
Figure 6: Strong fluorescence of the Propionibacterium acnes under UV-illumination of the Visiopor camera,
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®
SEr SEsc
(Roughness) (Scaliness)
(Wrinkles)
1.26 2.46
SEsm (Smoothness) 334.37 SEw
39.98 Figure 7: Calculation of skin texture with Visioscan. 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 damage will
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
other hand, increased sebum production is correlated to the occurrence of acne.21
On the 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® standard device to measure the sebum
is the
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® Sebutape®
or 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.
Evaluation of skin blemishes Blemishes are usually an indication that the skin condition is not ideal. They especially occur in acne and are often correlated to an increased sebum production. The occurrence of pimples and blackheads can be visually assessed and graded. This can be done based on direct inspection or for better comparison by the evaluation of high resolution photographs.21 The turn-out of photographs is strongly influenced by ambient light not only in reference to the light colour and intensity but also to the angle of light. Additionally, the position of the face and the angle of photographing as well as the distance between camera and face will have a huge impact on the outcome. Therefore, simple mobile phone cameras or even high-end consumer cameras are not the best-suited tools for taking such pictures. There is dedicated equipment available on the market that provides a homogeneous illumination, sometimes even the use of different light sources and a fixed positioning of face and other body sites for taking standardised photos. With such equipment, very reproducible and comparable images can be taken that are evaluated either by subjective scoring or by automatic calculation of the size of the pores and the amount of impurities. Sebum levels are highest in the face and
PERSONAL CARE EUROPE
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