CLEAR GEL ANTIPERSPIRANTS 229 The comparison of the stability results for formula 17 to 14, 15, and 21 18 to 14, 16, and 22 19 to 15, 16, and 23 and 25 to 21, 22, and 23 shows that at the levels studied, methenamine is more effective than all but acetamide MEA. The comparison of the stability results for formula 21 to 14, 15, and 17 22 to 14, 16, and 18 23 to 15, 16, and 19 and 25 to 17, 18, and 19 shows that acetamide MEA is the most effective of the five stability agents employed at the levels studied. Table III shows the result of formulating the five stability additives into one of Roehl's formulations (Formula 4/29). Formula 4/30 shows the increased stability achieved by using a less reactive solvent. Formula 4/31 shows the advantage of using acetamide MEA as both a stability aid and a solvent. Table IV shows the positive effect of incre- mental increases in the level of acetamide MEA on stability. Summarizing, the rank order of the effectiveness of the five stability additives at the practical concentrations studied is: acetamide MEA methenamine zinc acetate cocamide MEA magnesium sulfate. The concentration of additives was determined Table II Effect of Stability Additives on Gel Stability Formulation Constants % Dibenzylidene Sorbitol 3.0 Steareth- 100 1.0 Butylene Glycol 20.0 Hexylene Glycol 10.0 Aluminum Chlorohydrex 10.0 Stearic Acid, Triple Pressed 0.5 Hydroxypropylcellulose 0.2 Cyclomethicone 5.0 Formulation Variables Formula Number 13 14 15 16 17 lg 19 20 % % % % % % % % Ethanol, Anhy. 50.3 45.0 45.0 49.7 45.2 49.9 49.9 44.6 Magnesium Sulfate -- 0.3 -- 0.3 -- 0.3 -- 0.3 Cocamide MEA -- 5.0 5.0 -- 5.0 -- 5.0 Zinc Acetate -- -- 0.3 0.3 -- 0.3 0.3 Methenamine .... 0.1 0.1 0.1 0.1 Acetamide MEA ...... Stability Data: Days Until Completely Liquid @ 60øC 2 9 25 21 63 32 @ 45øC 35 263 445 445 445 445 Formula Number 21 22 23 24 25 26 % % % % % % Ethanol, Anhy. 40.3 45.0 45.0 39.7 45.2 39.9 Magnesium Sulfate 0.3 -- 0.3 -- 0.3 Cocamide MEA 5.0 -- -- 5.0 -- 5.0 Zinc Acetate -- 0.3 0.3 -- -- Methenamine -- -- 0.1 0.1 Acetamide MEA 5.0 5.0 5.0 5.0 5.0 5.0 Stability Data: Days Until Completely Liquid @ 60øC 102 60 123 247 247 247 @ 45øC 445 445 445 445 445 445 56 445 27 % 39.9 -- 5.0 0.3 0.1 5.0 247 445 98 445 28 % 44.6 0.3 __ 0.3 0.1 5.0 247 445

230 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table III Effect of Stability Additives on Gel Stability of Formula from US 4,154,816 Formulation Constants % Poloxamer 181 15.0 Cocamide MEA 3.0 Dibenzylidene Sorbitol 2.0 Triclosan 0.3 Aluminum Chlorohydrex 10.0 Stearic Acid, Triple Pressed 0.5 Fragrance 1.0 Formulation Variables Formula Number 29 30 31 32 33 34 35 % % % % % % % Propylene Glycol 28.7 -- -- 23.7 23.4 23.4 23.6 Butylene Glycol -- 68.2 -- -- -- Acetamide MEA -- -- 68.2 5.0 5.0 5.0 5.0 Magnesium Sulfate -- -- -- 0.3 -- -- Zinc Acetate .... 0.3 -- Methenamine ...... 0.1 Ethanol, Anhy. 39.5 -- 39.5 39.5 39.5 39.5 Stability Data: Days Until Completely Liquid @ 60øC 3 9-11 504 15 33 76 62 by solubility and aesthetic considerations. While magnesium sulfate and cocamide MEA apparently help stability, even together they do not improve stability enough to give a viable commercial product. Zinc acetate, methenamine and acetamide MEA alone or in combination appear capable of delivering a viable commercial product. The effect of these additives on antiperspirant efficacy will be the subject of a later paper. Table IV Effect of Acetamide MEA Concentration on Gel Stability Formulation Constants % Dibenzylidene Sorbitol 3.0 Steareth- 100 1.0 Butylene Glycol 20.0 Hexylene Glycol 10.0 Aluminum Chlorohydrex 15.0 Stearic Acid, Triple Pressed 0.5 Cyclomethicone 5.0 Formulation Variables Formula Number 36 37 % % Acetamide MEA 1.0 Ethanol, Anhy. 45.5 44.5 Stability Data: Days Until Completely Liquid @ 60 øC 3 4-6 @ 45øC 24 24 38 % 2.5 43.0 8 9O 39 % 5.0 40.5 20 367 40 7.5 38.0 59 367 41 % 10.0 35.5 169 367