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 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 acneswill 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 acnesand 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 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.  


Higher pH values at certain body sites like the axilla or the interdigital areas promote the colonisation of certain odourproducing or harmful bacteria and fungi.28, 29 


There are also other measurement parameters that can be used to show a positive effect on skin health. 


source from https://www.personalcaremagazine.com