SKIN RELIEF AND AGING 185 AGED PEOPLE o 270 ø 30 ø AR•t•iAXIS Figure 6. Rose of directions for aged people. Coordinate is the number of subjects having the principal or secondary axis at each 15 ø step. b) It seems that the secondary axis when it does exist becomes deeper with age, but only slightly as compared to the principal axis (Figure 9). 4. THE COEFFICIENT OF DEVELOPED SKIN SURFACE (C.D.S.S.) The C.D.S.S. increases with age: 1.16 _+ 0.01 for children (p 0.001), 1.18 + 0.01 for adults (p 0.01), and 1.20 _+ 0.01 for the aged subjects (p 0.001). The real skin

186 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS LINE DENSITY DEPTH 3O 20' 10 ! TT TTT Figure 7. Line density and mean depth of furrows from principal axis in each group: I--children II--adults Ill--aged people. jim 6o .4o .2o surface varies between 8 to 30%. This means that 1 cm 2 of skin represents an area of exchange of 1.08 cm 2 to 1.30 cm 2 (Figure 10). DISCUSSION The cutaneous region studied, the forearm, is a relatively covered area. It could be that changes detected in this site are provoked by aging and actinic radiation. Our results show that, until the age of forty, furrow depth does not change (Figure 8). After this age, modification of C.R. appears, and the principal furrow direction of the forearm is formed. At the age of fifty, the skin furrow depths start to increase continuously, to reach more than 100/•m after the age of eighty. In the same period (between 50 and 80 years) the secondary direction disappears and the furrow density of the principal direction is diminished. Looking at the aged skin, we can notice simultaneously four aspects related to surface structure: a) furrows in the principal direction are well marked by deep depressions b) the furrows in this direction are small in number compared to young and adult skin