452 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS dandruff and that you regard it as necessary to have a control group in parallel because the incidence of dandruff fluctuates at different times of the year? MR. VAN ABBg: The dandruff level of untreated subjects does not seem to be dependent on the season but we did see a sign in our earlier work that under active treatment there was a seasonal influence. Other factors might be involved too, such as holidays, examinations and various psycho-somatic influences that could make it difficult to draw conclusions without a placebo. M•ss DEAN: I should like to add that although we carry out concordance tests between examiners, this does not safeguard against all the examiners drifting in the same direction over a period of time. If we run a control panel, the observers do not know which product is control and which is treatment, so it does help to safeguard against any drift of this nature. Of course, using a placebo does put some people off they realise they are not getting better, and sometimes a proportion of our subjects get discouraged and tend to default if we keep them too long on no-treatment. MR. I(. M. GODFREY: IS the time required to re-establish dandruff affected by residual absorption of the active ingredients? MR. VAN ABsg: Possibly. Zinc omadine (the active ingredient referred to in the paper) is only soluble in water to the extent of about 6 ppm. Nonetheless it is soluble to this extent and may be absorbed or adsorbed this may contribute towards its efficacy, for some of it may be taken up during treatment and not be eluted for some time afterwards. MRs. S. M. LUDFORD: DO yOU use people again for assessment once they have recovered to their pre-treatment level if so, do they respond differently from new subjects? Do you observe any other effects of antidandruff products or do you only look for effect on dandruff? Mms DEAN: Occasionally we do use subjects again. We allow a considerable recovery period and, when using them again, we take great care to stratify them between the groups. We have supplemented the clinical examinations by looking for effects on Pityrosporurn and bacterial counts on the scalp. We pass an applicator through the subject's hair and take plate counts of micro-organisms. Sometimes we find a reduction but so far we have not really demonstrated any definite correlation with dandruff scaling. MR. VAN Assi: We also record itching and erythema, again without showing any distinct correlations. MR. K. V. CURRY: IS the response of the moderate/severe group of subjects similar to the response of the "very slight" group? I have a feeling that the majority of people with dandruff have the second type which is really a social nuisance rather than a scalp disorder. M•ss DEAN: On the whole it is easier to show a significant reduction on people who have severe dandruff and for the bulk of our panels we prefer to use such subjects. I think the proportion showing a reduction who start with slight dandruff is nearly as great as for those who start with a severe level but, of course, it is not such a great reduction. MR. R. CLAm•: Is your objection to the use of vacuum cleaner technique purely theoretical or is it based on practical experiments?

THE CLINICAL EVALUATION OF ANTIDANDRUFF SHAMPOOS 453 MR. VAN ABBI•: We have carried out some experiments. We did not like the Hair Vac (as used by Vander Wyk) in its original state but even when this had been modified by us, we still felt that it was impossible to know whether the course of the con- dition was being influenced. This is the main difficulty, for one just cannot know and therefore it does not seem to be a desirable technique. MR. R. CLARK: Did you run a "vacuum cleaner" trial in conjunction with your own subjective method of assessment? MR. VAN ABBi: We have not done so yet, although we have considered the possibility.