18 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS types of published method, visual or colorimetric, continuous humidity assessment and gravimetric. The basis of the colorimetric method is to apply an anhydrous indicator to the skin and to observe the extent of colour formation, when sweat is produced. A developer may also be used to produce the colour, which is usually in the form of individual dots, each dot corresponding to a sweat gland. The disadvantage of this type of method is that it is not readily quantitative, and that it is only applicable to flat, accessable areas of the body such as the back or fore-arm. Many workers have studied the colori- metric approach and Daley (1) has produced a quantitative method that has given good agreement with other methods. It did, however, require a large area of skin such as the back, and depended on a numerical count of dots, not taking into account their size or intensity. The continuous humidity approach is almost the opposite to the gravi- metric in that it is readily suited to axillary sweating measurement, and is fully quantitative. It depends on directly measuring the humidity of the air in a cell held in the axilla, and sophisticated adaptions produced by workers such as James (2) are capable of giving a direct print out on an x-y recorder of the sweating ratio between axillae. The objection to the method is that the subject is severely restricted in movement, and adaptation to normal conditions of use is not really feasible. Most attention in recent years has been directed at gravimetric methods of assessing perspiration flow, as they are direct or absolute and reasonably convenient. Much of the early work in this field was conducted by Fredell and co-workers (3, 4). Their method was to use pre-weighed absorbent pads held in place in the axilla without a harness for a fixed period of time. The increase in weight of the pad was a measure of degree of perspiration. The daily variation of weight of sweat produced by individuals was found to be high, but the ratio of sweat produced from one axilla to the other for an individual was reasonably constant. If after a control period only one axilla was treated, the change in ratio was a measure of antiperspirant effect. It was necessary with this sweat collection technique, however, that the subjects were static, and a hot room to induce perspiration was required. This method is the basis of the procedure used by Hill Top Research Inc., and typical results obtained using this procedure have been published by Martin (5). The great advantage of using the change in ratio as a measure of antiperspirant effectiveness is that it is independent of the absolute weight of sweat collected, which can vary considerably even under fairly controlled conditions.

EVALUATION OF ANTIPERSPIRANTS UNDER NORMAL CONDITIONS 19 To adapt the gravimetric method to be suitable for assessing anti- perspirant preparations under normal conditions of use, Wooding et al. (6) used silica gel drying tins of the type used in analytical balances. These were strapped to the backs of subjects and had the advantages of being easy to handle, reusable and efficient. From consideration of the different types of procedure described above, it was clear that the gravimetric method was the most adaptable for assess- ment of antiperspirant effect under normal conditions of use, if the ratio technique was employed. As to the method of sweat collection, it was found, after experimentation, that the moisture absorbing tins of Wooding et al. could be strapped to the body side of the axilla with waterproof tape, without greatly inconveniencing the tester, and that they gave more reliable and accurate results than the various pad and cup arrangements tried. The experimental method described in this paper is, therefore, a gravimetric one, whereby silica gel moisture absorbing tins are used to collect axillary perspiration and the change in ratio of sweat production between axillae for an individual, when only one axilla is treated, is a measure of anti- perspirant effect. TEST PROCEDURE The particular moisture absorbing tins selected were Silica Gel Air Dryers*, size No. 2, 60 mmx 9 mm (Fig. 1). These are perforated disc- shaped containers of silica gel, which are capable of absorbing 8-9 g of moisture. They are supplied in aluminium outer containers. The rate of loss of moisture by evaporation, from a used tin, is negligible for a tin in its container left on the bench for half an hour. Thus, during the time that the tin is removed from the axilla, placed in its container and weighed, there is negligible evaporation of sweat. The waterproof tape used is a micro- porous, plastic, self-adhesive plaster, Elastooe1ast Airstrioe?, which was supplied in rolls 1« inch wide. The tins and containers were numbered, and were used randomly during a test. ß At approximately 09.00 every working morning, the tins were weighed in their containers to the nearest milligram. Subjects were asked to dry their axillae with tissue paper, and the tins were removed from their * Silica Gel Limited, London,. ? T. J. Smith and Nephew Ltd, Hull and Welwyn Garden City.