THE EVALUATION OF A SHAMPOO By WM. W. MYDDLETON, D.Sc., F.R.I.C.* THE SHAMPOO user is supremely conscious of one characteristic, foam- iness, which, therefore, above all others, influences his judgment of shampoo quality. The fact of the independence of foaminess and the cleansing action, for which pre- sumably the shampoo is purchased, brings about no relaxation in the general demand for a shampoo which lathers freely. In 'this paper it is proposed to deal with the assess- ment of shampoo value on the basis only of foaming power, which is the veritable sine qua non of the popular shampoo. The evaluation of a shampoo may be required either for the major project of assessing the appeal of the product to the shampoo-using public or for quality control in manufacture and for the selection, grading and blending of raw mater- ials to be used in manufacture. In the present discussion we shall con- sider only the assessment for quality control and examination of raw materials. The ultimate test of shampoo quality must be its per- formance on the head, but, as we shall see, great care must be taken * Chief Chemist, County 12erfumery Co. Ltd., London. in the planning of the test and in the interpretation of the results. In a practical shampoo test we have to decide first of all who is to operate, who is to make the observations, and on what type of head the test is to be applied. Secondly, we must know what observations are to be made, and what conditions of opera- tion will provide the most reliable information. It will be useful for us to examine first of all the nature of the evidence we require to collect. It must cover all those features which the critical user will expect to find in a shampoo, namely: (a) The product must have an attractive appearance. (We are not considering the attrac- tiveness of the pack or its presentation, but of the sham- poo material itself.) (b) It must be simple in applica- tion, for example, if it is a cream shampoo it must be easily extruded from a tube and easily spread on the hair. If a powder, it must dissolve readily without scattering irri- tant dust. (c) There must be no failure to foam on the first application, 150

THE EVALUATION OF A SHAMPOO and the first rinsing should remove practically all the dirt from the hair. The second application must produce a copious lather. (d) It must be easily rinsed out of the hair. (e) The hair must be clean and glossy and in good condition when dry. (f) The perfume must be pleasant throughout the operation. (g) There must be no scalp irrita- tion. For purposes of control. we can carry out only a limited number of shampoo tests to determine whether the shampoo is capable of filling these requirements. The shampoo when applied to one's own head can- not be used so effectively and easily as when it is applied by a second person, who is also better able to judge the cleanliness, gloss and general condition of the hair. It is therefore essentiM that the opera- tion should be carried out by some experienced person who would natur- ally be the one to make and record all the observations, with the excep- tion of such as (g). We have now to consider some variables in the working conditions. The most important is that all heads are not alike in their reaction to a shampoo. For example, greasy or dirty hair will tend to depress the lather of the first application and may even suppress it entirely. Not only so, but the very texture of the hair, whether fine or coarse, •511 affect lathering power. For this reason, when only a limited number of test shampoos can be carried out, it is desirable to divide the hair into two parts, left and right, down the middle line. One side is treated with a reference shampoo and the other with the one under examination. It must be observed here that, while we are by this means reducing a major cause of discrepancy, we are introducing a minor one. The positioning of the operator with reference to the two sides of the head makes it easier for him to manipulate one side than the other, and this is quite apparent at times, particularly when a fatigue effect develops in the course of the somewhat strenuous application of the shampoo. This disturbing factor is miniraised when each shampoo is used on an equal number of left and right sides. The saloon method is made more selective by diluting the shampoo before use with tap water to some arbitrary standard of concentration which may differ according to the purpose of the test. Very high con- centrations fail to show minor differences and may not reveal what we are really most concerned in finding, namely, whether a given shampoo is likely to fail to produce a lather on the first application in a significant number of cases, under the average variations in the condi- tions of customer usage. A useful level of concentration is around 0'25 per cent of active foaming agent or, if this should be difficult to assess, 0'5 per cent for a powder shampoo, 1'0 per cent for a 151