EMOLLIENCY AND CHEMICAL STRUCTURE 639 ment if these were incorporated in a typical cream or lotion, rather than trying to feel them "pure." The second requirement of the base formula was that it be stable, with emollient content as high (37%) as practicable, so that the primary feel would be that of the emollient under test. Deliberate use was made of a TEA-stearate soap emulsifier system containing excess stearic acid to provide a "background" raspiness and drag which each emollient had to "overcome" before it could score well. Additional emulsion stability was provided by a generous amount of glyceryl monostearate, to insure that we would not obtain mixed (O/W -]- W/O or O/W/O) emulsions, which have a peculiar skin feel all of their own. Table II shows the evaluation of a Control Lotion, where water was substituted for the 7% emollient used in all other tests. This table also shows details of the numerical rating system used to determine the Skin Table II Control Lotion (No Emollient) Viscosity (25øC) = 912 cps Oil phase 4.0 % Glyceryl monostearate (pure) 3.0 Stearic acid XXX Water phase 4.0 Propylene glycol 0.5 Triethanolamine 0.4 Sodium lauryl sulfate 88.1 Water 100.0% Initial Slip = 4.0 (Scale 1-5 = slight to much slip) End Feel = 10.5 (Skin Feel after complete dry-out, the summation of four factors, each judged on a 1-5 scale. Total End Feel scale is therefore 4-20). End Feel Ratings 1 2 3 4 5 Smoothness 2.5 Poor Fair Good Smooth Friction 3.0 Tacky Skids Drag S1. drag Oiliness 3.0 Dry Dry/waxy Waxy Oily/waxy Moistness 2.0 Very dry S1. dry Neutral Sl. moist = 10.5 Velvety rich Slips Oily Dewy Skin Feel Index (SFI) = 4.0/10.5

640 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Feel Index (SFI) of various emollients. The SFI is the ratio of Initial Slip/Total End Feel. Initial Slip was considered very important, and was rated per se, on a 1-5 scale (slight to much slip). Middle Feel could not be ranked reproducibly, since qualities such as "absorption time" are highly variable, depending on skin type. Creams would "rub in" quicker on a dry skin than on an oily skin, and absorption time varied greatly with the location to which cream is applied. Palms, for exa•nple, absorb very little. End Feel was divided into four subcategories, as shown in Table II. With very little practice it is possible to describe quite reproducibly the sensations of smoothness, friction, oiliness, and moistness. The same in- vestigator was able to repeat his own results at any given time, or his own results a week or a month later, or the results of other investigators. Overall SFI scores were reproducible within approximately 10 to 15%. This reproducibility is the primary justification for presenting the data which follow. The SFI evaluation procedure relieves us of the necessity to ask dozens or hundreds of persons to evaluate each product. The SFI scores of over 85 different cosmetic emollients are reported below. RESULTS The Control Lotion (no emollient, Table II) showed an Initial Slip 4.0. Its End Feel score of 10.5 is the sum of the following four corn- ponent scores: S•noothness 2.5 (fair to good s•noothness) Friction 3.0 "(drags) Oiliness 3.0 (waxy) Moistness 2.0 (slightly dry) 10.5 (out of a possible score of 20.0) This control lotion was almost perfect for our purposes, since it gave quite average results (SFI z 4.0/10.5). Its Middle Feel was also quite mediocre, showing values of 3.0 for "break" quality, medium "absorp- tion time," and a 3.5 value for "change in texture." This lotion becomes extremely draggy during the transition period to complete dry out. Materials which show SFI scores below the 4.0/10.5 Control Lotion score are likely to worsen the skin feel of emulsion cosmetics. Materials showing substantially higher scores can presumably improve them.