SKIN RELIEF AND AGING 181 5. 'FHE COEFFICIENT OF DEVELOPED SKIN SURFACE = S E When two axes do exist, one can calculate EMt for axis 1, and EM2 for axis 2: SE = EM• {1 + (EM2- 1) sinfi} where fi is the angie formed between the two axes. This coefficient is of great interest in studies including measurements relating to exchanges between the skin and its surroundings. It gives the real area involved in migration through the skin barrier (02, CO2, H20) and corrections should always be made taking into account this coefficient. In the case of a single axis, EM2 is equal to 1, and: SE = EMp RESULTS The study was done on the volar forearm of 116 subjects, from 2 to 98 years of age, and classified in three groups (Table I). TABLE I ( : : ) ( "GROUP : AGE CLASSIFICATION (YEARS) : NUMBER : TOTAL NUMBER PER GROUP ) ( : : : ) ( : ( I : ( Children : ( : : : ) 0 - 9 : 18 : 38 ) 10 - 15 : 20 : ) : : ) : : ) 20 - 29 : 9 : ) 30 - 39 : 7 : ) 40 - 49 : 6 : 42 ) 50 - 59 : 9 : ) 60 - 64 : 11 : ) : : ) : : ) 65 - 69 : 5 : ) 70 - 79 : 23 : 36 ) 80 -100 : 8 : ) : : ) ( : ( II : ( : ( Adults : ( : ( : ( : ( : ( III : ( : ( Aged people : ( : 1. THE NUMBER OF DIRECTIONS Two main furrow directions are detected in the children's group. The second axis disappears progressively with age, and is almost absent in aged people, as shown in Figure 3. 2. THE ORIENTATIONS A graphic representation in polar coordinates, called rose of directions, plots in 15 ø intervals the number of people having that direction to their furrows. For example, when we detect two orientations, the first one at 60 ø (plus the complement at 240 ø ) and

182 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 100' 75' 50- 25 10 20 30 40 50 60 70 80 90 AGE Figure 3. Histogram showing % of subjects lacking the secondary axis when classified in ten year age groups. the second one at 0 ø (plus the complement at 165ø), such a subject will be plotted four times on the graph. An aged subject, having a single orientation, will be plotted two times. This graphic representation has two advantages: it gives the general orientations in the whole population studied and the spatial symmetry or asymmetry of these orientations to each 180 ø measurement. Thus, in each group, arrows indicate both when a main orientation appears and the geometric mean angle directions related to arm axis (Figures 4 to 6). ß Children's group (Figure 4) The principal axis is found at 65 ø, and shows homogenous representation. The secondary axis is principally oriented at 165 ø, but some skins show a secondary axis at 15ø-195 ø . ß Adult group (Figure 5) The principal axis is found at 50 ø . The secondary axis is placed between 150 ø and 15 ø , although it has an average position of 165 ø and is less stable than the corresponding one of the children's group. ß Aged group (Figure 6) In this group, the secondary axis has disappeared. Some people have their single axis oriented at 0 ø, others at 50 ø (and complements at 180 ø and 225ø). The dispersion of values is very high. An explanation of this might be the different positions taken by arms when replicas Were made, as related to the loss of the skin extensibility in aged people, discussed latter.