226 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Distribution of Levarometry ø•Age 20-39 Y 30 E 20 o 100 88 82 84 63 40 0 0 N:84 11 21 31 41 51 61 71 - -• 81 20 30 40 50 60 70 80 -- Elevation x 10 -3 cm Figure 3. Distribution of levarometry. The "young age" (20-39 years) cases are shown by a dotted line. The unbroken line shows the total number of cases. coefficients (hair graying score and metacarpal osteoporotic index). The generally low correlation coefficients of age-dependent processes as compared to other biological cor- relations reflects the fact that biological aging is poorly correlated with chronological aging. Once we have a statistical evaluation as shown in Table III, we can establish a "desired" range of that parameter, based on some statistical assumptions. Conversely, any value outside the above range shows the effect of aging, and cosmetic treatment is therefore worthwhile. In our data, superimposing the range given in Table III onto Figures 1-4, we can in fact see that about at the limits given by Table III, the percentage of "young" cases starts to decline. The percentage of women by age groups, whose skin parameters are outside the limits given in Table III (therefore presumably showing the effects of aging) has been published elsewhere (4). Age dependence of physical parameters has been published in earlier literature (for review, see reference 3), but no detailed analysis of

AGE DEPENDENCE OF SKIN PROPERTIES 227 Distribution of forehead pH. 125 - Age 20-39y: 100 100 76 •: 100 - 75 t 5o 25 69 71 77 74 86 27 90 70 80 ß ß N: 500 I ee eee 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 4.3 4.5 4.7 Figure 4. Distribution of forehead pH. The "young age" (20-39 years) cases are shown by a dotted line. The unbroken line shows the total number of cases. Table III "Young" (20-39 Years) Range of the Measured Parameters 95% Confidence Limit Mean (20') Indentation 41 x 10 -3 cm -+ 8 x 10 -3 cm* Elastic recovery 78% _+ 10% Levarometry (slackness) 41 x 10 -3 cm +- 25 x 10 -3 cm pH pH 5.3 +- 0.8pH * 24.6 -+ 4.8 units the "normal" versus "desired" range has ever been presented. In analogy, for an anti- pyretic drug we know at what body temperature to start using it and what the desired normal temperature is. For a drug, one has to show that in field situations the prep- aration restores the measured parameter to the normal range in a statistically significant percentage of cases treated. Such analysis is very important if we wish to develop skin care products with scientifically proven value, to combat aging aspects of the skin.