Examination of sebum 325 The whole of the panel was classified according to increasing value of Z 0. From this classification, the histogram in Fig. 9 was drawn based on the conclusions of the clinical examination. IOO • 5o 26 31 36 41 46 51 56 Figure 9. Distribution of seborrh½ic subjects according to values It is to be noted that the percentage of seborrheic subjects increases with values included between 26 and 36 no cases of seborrhea were found. As a corollary, above z 6 = 51 only seborrheic individuals were found. These two groups represent 20•o of our population. For these subjects the determina- tion of z6 gives a perfect correlation with the diagnosis. Between these two limits, the probability of finding seborrheic subjects increases with the value of Z 6. This fact shows that for 36 • • Z 51 there is no absolute and perfect correlation between the conclusion of the clinical examination--which is subjective--and the para- meter Z 0 which is measurable. This finding is not surprising the clinical examination includes a complex reality where there is simultaneously: the quantity of sebum secreted per unit time (possibly corrected by a factor related to the mass and to the surface state of the hair), the quality of sebum which is related to its physical properties (spreading, viscosity, melting plot... ). The method used only included the qualitative parameter. There are other measurable parameters which define this notion of quality of sebum, especially viscosity. Other parameters directly bound to composition are: percentage of squalene iodine number the ratios of the quantities of palmitic and palmitoleic acids. These parameters were determined for the whole population, to see whether they are in correlation with The correlation is positive with iodine number and percentage of squalene, negative with viscosity and the ratio quantity of palmitic acid (Fig. quantity of palmitoleic acid These correlations are readily explicable: a high zo shows that the melting signal is important in the low temperature range. In other words, at ambient temperature, the larger is the liquid fraction of sebum the higher is Z6. Similarly high z 0 values must

326 Pierre Bard and No•'l Goetz 5O ,,, 4O 3O _ I I I 5 I0 15 % Squalene , I I I 80 90 I00 I10 Iodine value 5O 3O 4- I I I I I , I I I 2 • 4 5 1 2 Viscosity Polmillc acid PolmlioleJc acid Figure 10. Correlations between •"6 and some physico-chemical parameters. 5C- 40- 30 G G N N G\G G G GN N NG N N N N N • G N N N N N GN N N G G G NG G G G G N N N NN ß I I I, t 500 1000 1500 2000 Weight of sebum per head(mg) Figure 11. Relation between quantitative and qualitative parameters.