402 D. C. Cullum selected must also be as constant as possible, otherwise the random variations which must inevitably occur may be so great as to make it impossible to fulfil these conditions. The parameters to be considered include but are not necessarily limited to the following: sweat weight from an individual axilla sweat weight from an individual subject ratio of sweat weights from right and left axillae of an individual subject ('R/L ratio') mean sweat weight, geometric or arithmetic, for a group of axillae or subjects and mean R/L ratio, geometric or arithmetic, for a group of subjects. The best parameter to use is the one which shows the least variation. In practice the choice may be influenced by other constraints. It is essential to appreciate that none of these parameters is necessarily among those which the user employs to assess efficacy. For example, common sense suggests that in normal use the consumer can observe only inefficacy. That is, if she perceives that she is not sweating, she cannot tell whether her antiperspirant is working or whether she would not have been sweating if she had not used it. If she perceives that she is sweating, however, she is likely to interpret that fact as evidence that her antiperspirant is not working. Secondly, she will observe that she is sweating through some signal such as wet patches on her clothing. The connection between presence or absence of wet patches on clothing and variations in the number of milligrams of sweat on absorbent pads may be a tenuous one. The user's judgement may also be influenced by the various sensory impressions she gains when she applies the product, and by the characteristics and persistence of the perfume. There is therefore no a priori reason for supposing that anti- perspirant efficacy as measured in the hot-room will correlate with efficacy as perceived by the user, because the parameters employed are necessarily different and may be quite unrelated. PROTOCOL The protocol, that is the manner in which the method of measurement is to be applied, is determined by the parameter to be measured, and by any ancillary information which may be required. For example, antiperspirants based on aluminium chlorhydrate often show only a modest effect in tests conducted up to 24 h after the first application (6). With daily or twice-daily application, the effect increases and reaches a plateau after a period which may be as long as 14 days. If it is desired to observe this build-up, repeated hot-room sittings will be necessary, but for routine testing of development products it may be adequate to take only one observation. In this case the result will be influenced by the number and frequency of product applications preceding the test, and a test done after three daily applications will be neither better nor worse than one done after eight twice-daily applications it will merely be different. Cross-over designs have been advocated to minimise the effect of side bias. If this type of design is used it is necessary to allow at least 2 weeks to elapse between the two halves of the test to permit the effect of the first set of treatments to disappear. Provided the number of subjects is large enough, application of each treatment to equal numbers of left and right sides will miniraise side bias to an acceptable extent without the need for a cross-over. Just how many subjects are enough depends not only on the level of statistical discrimination required but also on the need to use a sample reasonably representative of the population at large. It might be possible to devise a procedure which would discriminate significantly between two products whose efficacies differed by only 5•o with the use of say twelve subjects. Twelve subjects, however, would be unlikely to constitute a reliably repre-

Rapid hot-room testing of antiperspirants 403 sentative sample, in which case repeating the test on another group might give a very different but equally precise result. The sample should be big enough not only to give acceptably narrow confidence limits, but also to give reasonable certainty that the result obtained is typical of the population at large. The taking of a single observation on each subject obviously maximises the sample size for a given number of hot-room sittings. THE METHOD Subjects. Female subjects are used exclusively, because male subjects are not available in substantial numbers during normal working hours, and because a majority of anti- perspirant users are women. Before being accepted on to the test panel, each subject undergoes a screening test to determine whether her sweat output in the absence of antiperspirant treatment is sufficient for her to be useful. The lower limit of acceptability has been arbitrarily set at 100 mg per axilla over a 20 min collection period. This test is preceded by a 2 week period during which the subjects are supplied with an alcoholic deodorant product. Once they have been accepted, panellists receive a continuous supply of the same product for home use. Frequency of participation. No subject is used more frequently than once every third week. This is to permit the effect of test products to disappear. Protocol. Subjects attend for three consecutive days. They are treated with the products once daily and on the third day take part in a hot-room test. No cross-over is used. Normally up to fifty subjects are used for each test. Products. Two products are used per test, designated the test and control product respectively. The control product may or may not be without antiperspirant effect, i.e. a true placebo. Product application. The products are applied by a member of the hot-room personnel. For aerosols a 2 sec spray is given from a distance of 6 inches. Solutions are applied by pump-spray. With roll-on products the subjects are normally asked to apply the product themselves. Alternatively an attempt is made to apply 200 mg of product per axilla, but the size and topography of individual axillae cause considerable variation in the amount actually deposited. Half the subjects, selected randomly, receive the test product on the left side and the control product on the right, while the other half receive them the other way round. Hot-room procedure. Before each subject enters the hot-room, a pair of unweighed absorbent cotton pads (the 'A' pads) are placed in her axillae. She then sits in the hot- room for 40 min to allow her sweating rate to approach equilibrium. The A pads are removed, the axillae are blotted with tissues and a weighed pair of pads (the 'B' pads) are placed in position. After 20 min these are removed and put into airtight polythene jars. The axillae are again dried with tissues and a second weighed pair of pads (the 'C' pads) are applied. After a further 20 min these are removed and put into airtight poly- thene jars. During the 80-minute hot-room sitting subjects may have hot or cold drinks on request, and are permitted any activity compatible with retaining the absorbent pads in the axillae. At the end of the session, subjects shower and go home.