COSMETIC KNOWLEDGE THROUGH INSTRU- MENTAL TECHNIQUES* BY E.G. McDoNOUGH, PH.D.,D. A.M. M^cv.^¾, PH.D. ^HI) M. Bl•v.I)IC•., PH.D. Evans Research and Development Corporation, New York 17, N.Y. TRADITIONALLY, the cosmetic field has been a very difficult one for the chemist and analyst. A study of the development of the cosmetic in- dustry, however, shows the increasingly large part that science has played in it. The science referred to is made up of many parts, such as derma- tology, physics, chemistry, toxicology, etc., but it is probably the science of measurement as much as anything that is lifting the cosmetic industry from the slough of empiricism and setting it firmly on its feet as a field of genuine scientific endeavor. Lord Kelvin said, "If you can measure that of which you speak, and can express it by a number, you know something of your subject but if you cannot measure it, your knowledge is meagre and unsatisfactory." ,Un- fortunately, cosmetics have offered many examples where it has not been possible to "measure that of which you speak." Historically, cosmetic research can be divided roughly into three phases. In the first, the emphasis was on the gross physical properties of importance to cosmetics, such as color, texture and particle size. During this period many vague subjective terms, such as "oiliness, .... creaminess" and "smooth- ness" were in vogue, but apart from rough classifications of physical proper- ties very little actual measurement was involved. The second phase was stimulated by the rapid development of the chemical industry, with a resultant realization of the importance of product control methods and of specifications for the purity of raw materials and of finished products. The recent availability of synthetic materials and their use to replace natural products were also factors in this new awareness of the importance of chemistry to cosmetics. The chemical nature of fats and waxes was realized to be important to product performance and stabil- ity, acid numbers, iodine values and saponification numbers became valu- able measurements when their correlation with such properties was es- tablished. During this period the emergence of hair waving based on scientific * Presented at the December 13, 1956, Meeting, New York City. 126

COSMETIC KNOWLEDGE THROUGH INSTRUMENTAL TECHNIQUES 127 principle occurred. The mechanical phase of hair waving was supplanted by the chemical phase (1). Manual dexterity with the hot curling tongs was replaced by mental dexterity in the cold light of scientific research. This led to the seemingly paradoxical use of mercaptans in cosmetics (2), a development which appeared to fly in the face of the entire experience of the cosmetic industry. These mercaptans have been used in waving lotions and depilatories in a powerful demonstration of the superiority of the scientific method over curling iron, razor blade, tweezers and depilating wax. The third phase, which we have entered but comparatively recently, can be called the "era of physico-chemical measurement," a development which should make Lord Kelvin rest more easily. We have seen the gradual development of measurement techniques to aid cosmetic research in control work and in the evolution of new processes. We have pH, colori- metric and viscosity measurements on the one hand, and empirical measure- ments for detergency, foam stability and emulsion stability on the other. Probably the uses in analysis have had most emphasis, but the new instru- mental techniques are also very valuable for determining the effects of cosmetics upon hair, skin and teeth. They show the functioning of proc- esses, the absence of undesirable effects, the creation of desirable effects and the way to even better cosmetic products. It is important these days to show that cosmetic products not only cover blemishes and change the color of the skin and hair, but also that they pro- duce soft and smooth skin, better combing, increased luster and improved hair manageability. Unfortunately, methods for measuring these proper- ties are not always at hand, and the problem of measurement arises. How should the measurement be made ? By human senses or by machine ? On fundamental properties or on some empirical basis ? Before attempting to answer these questions, certain generalities, often overlooked, about instruments should be considered: (1) Instruments are developed for the convenience of man. They are designed to give him information more conveniently and more accurately than he could get the same results by hand. (2) An instrument is a measuring device which can give information on three levels: (a) bulk properties, (b) molecular properties and (c) atomic properties. Most instruments can be classified accordingly. (3) An instrument is designed to fill a gap in knowledge. The instru- ment for a given application is chosen according to the type of knowledge that is needed to solve a given problem. (4) The area where the knowledge is needed governs the design of the instrument, rather than of the instrument governing the field of applica- tion. (5) The results given by an instrument will be meaningful only in re-