44 TESTING
on the scalp. Especially, Propionibacterium acnes, preferring anaerobic environments, thrive in oily conditions and, combined with other factors, can cause acne. The porphyrins produced by the Propionibacterium acnes will show an autofluorescence when exposed to UV light of special wavelengths.24
Using cameras
providing such light sources can therefore demonstrate the activity of the Propionibacterium acnes and show the effect of products. Special software can evaluate the number, area and intensity of such fluorescences for comparison of untreated to treated skin.
Evaluation of skin irritation Skin irritation will show in increased microcirculation visible as an increased redness.25
Its intensity can be assessed by subjective scoring by experienced scientists. The human eye is however not able to evaluate very small differences and compare them to colours that have been previously seen at a different examination day. Photographs, taken in standardised conditions, will assist the researchers in grading of redness. Instead of subjective grading, image colour analysis can also be automatically performed by special software. Besides comparing pictures, colour
measurement to assess redness is often done by probes that are quicker and easier to use.
Skin Colorimeter® and Chromameter®
probes are emitting white light and apply colour detection sensors to determine the colour, transferring the results to Cie L*a*b* units. These values describe the colour in its brightness (L-value), its position on a red-green (a-value) and a blue-yellow axis (b-value). Since the main chromophores in the skin
are hemoglobin from the blood and the melanin, narrow-band spectrometers such as the Mexameter®
use only specific
wavelengths that offer a clear distinction between melanin and erythema. The Mexameter results for redness and pigment are displayed as arbitrary units with a high resolution between 0-1000 and can be very easily interpreted and compared.
Skin topography
Of course, healthy skin should show a regular texture and no open cuts or increased cornification providing a stiff skin surface and hiding the fine texture lines. Assessment of the skin texture using imaging techniques will show if there is an improvement of the skin condition. Different methods such as fringe projection (PRIMOS®
, FOIDS® ), Visioscan® or shadow
analysis of silicone replica can be applied to assess changes in the skin texture.
Desquamation assessment From the depth of the epidermis, new
PERSONAL CARE EUROPE
Class 1 Class 2 Class 3 Class 4 Class 5 All
Area (%) 12.21 28.34 37.9
13.62 6.02
98.09 Figure 8: Desquamation measurement with Visioscan using corneofix tape.
keratinocytes are constantly produced and migrate slowly to the outer skin layers. During their journey, they will undergo several processes and will end up as flat corneocytes in the stratum corneum that will finally be shed from the skin surface. This shedding process is called desquamation. It is an indicator for enzymatic processes taking place in the skin and has also been linked to skin barrier quality.17
The desquamation of healthy skin
should be fine and regular. To the eye, it is invisible. If the desquamation process is disrupted, some only partially detached corneocytes will accumulate either as isolated islands or as a whole combined with a thickening of the stratum corneum. The severity can be graded, from barely visible flaking and a slightly rough skin surface to the collection of very thick flake aggregations, clearly visible to the eye.26 The desquamation of the skin surface can be determined using imaging techniques, applying special sticking tapes to the skin and removing them. The loose corneocytes will stick to the tape and their distribution and thickness can be calculated.
Determination of the skin-pH-value Skin pH is essential for the wellbeing of
specialised bacterial communities. The body’s internal environment retains
a more or less neutral pH value of 7-9. From neutral pH values in the lower epidermis, there is a steep decrease of pH values towards the skin surface. Depending on the body site, age, gender and many other intrinsic and external factors, values of the surface mainly range between pH 4-6.27 The acidic pH-value towards the skin surface and in the hydrolipid film is attributed to different factors such as free fatty acids from the lipidic excretions of the sebaceous glands, lactic acids from the sweat glands, microbial and endogene processes and other influencing parameters. Cleaning the skin with soaps will lead to a short term shift of the pH value, but healthy skin will be able to balance this disruption within a certain time span. Frequent washing can however lead to cumulative effects and can seriously harm the skin barrier.28 The acidic pH environment on the skin surface is not only, as previously assumed, a protection against invading organisms. More recent studies have demonstrated that the formation of important enzymes necessary for triggering barrier-related processes is very much dependant on specific pH-values.
April 2019
Area(mm2 3.52 8.16
10.91 3.92 1.73
28.24
)
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