ASPECTS OF CHELATION IN COSMETIC PRODUCTS 269 immunity, antioxidant property, preventing discoloration and skin irrita- tion due to presence of heavy metal ions. Even synthetic-based hard soaps designed for hard water areas still lack the cleaning action desired. EDTA is the answer, but for the present, economics limit its use in this area though soap plus EDTA should become greater competition to the syn- thetic bar. Where bacteriostats are employed in soap products, discoloration, deactivation and skin irritation may be problems created by reaction with heavy metal ions. Some bacteriostats are reactive with ferric ion and become primary irritants so that chelation is a safeguard measure. To create a white soap or pastel shades requires proper choice of fatty acids, whitener or colorant, perfume and bacteriostats plus chelation for shelf-life stability. Again, the only function performed by the presence of EDTA or DTPA is as a protective measure to set up competition for the trace metal ions and lower their ionic activity to such low values that catalytic or color reactions to develop will require a time lapse of thirty days, ninety days or may never occur. Another aspect of chelation important to recognize with soap or the use of bacteriostats is the prevention and dissolving of calcium soaps. Calcium soaps are insoluble in water but dissolve in the oily secretions of the sebace- ous glands. EDTA, by dissolving calcium soaps, helps cleanse the skin and prevents the entrance of bacteria into the skin and also exposes the bacteria to the destructive action of sodium soap. The cleaner the surface of the skin the more effective exposure to the action of the bacteriostat. The use with hair dyes is similar to the established practice throughout the textile dyeing industry. The presence of EDTA will help level the dye and dye take-up. Its prime function is to cleanse the hair surface of impeding metal ions. Aromatic diamines and aminophenols require the addition of a reducing agent to act as a stabilizer and prevent oxidation during storage. EDTA will definitely promote greater stability of the reducing potential of the dye system since trace metal ions such as ferrous and cupric ions catalyze the reaction of the reducing agent with atmos- pheric oxygen. Any oxidation treatments involving bromates or peroxides are stabilized to a marked degree by either EDTA or DTPA. The chelating agent acts also as a protective agent against hair damage since mordanted metal ions act to localize and catalyze the oxidative action of the bleaching agent. A glance at the log K values for DTPA'versus EDTA with iron and copper ions plus the fact that DTPA is more stable to peroxide than EDTA desig- nates the use of DTPA as the stabilizer for any oxidative treatment of hair. Where stearic acid is the basic ingredient of formulations, such as vanish- ing creams and brushless shaving creams, it has been reported that these creams made with certain alkalis tend to darken with age and strict atten-

270 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS tion must be given to the absence of metallic contamination. The use of EDTA in the acid form solubilized with the desired base for compatibility should prevent this darkening with age and also assist in the cleaning function of the preparation. Simply add the EDTA acid before the addi- tion of the base. This brings up the question of the toxicity of EDTA and DTPA. In the concentration necessary to accomplish the ends described previously in this paper, and within the pH limitations of cosmetic products, neither of these materials presents any toxicological problems. Actually the utility and amounts used in cosmetic products place their relative toxicity far below that of alkalis, reducing or oxidizing agents commonly used by the cosmetic industry. Chelation is spreading into many new cosmetic formulations but old products and soap preparations are areas where chelation can improve the end-use performance and make such products very competitive with syn- thetics. When employed correctly, either EDTA or the new chelating agent, DTPA, should be the solution to problems involving trace metal ions. The cosmetic chemist should look to these two chelating agents for the solution of problems dealing with interplay of metal ions and competing anions as well as enhancement of many soap-based cosmetic preparations. The writer gratefully acknowledges the foam protection data proved by Dr. A. K. Prince and Mr. Norman Picard of the Technical Service and Development Department, The Dow Chemical Company, Midland, Mich- igan. THE PRESENT ROLE OF DETERGENTS IN TOILET BAR MANUFACTURE BY JOHN W. McCuTCHEON* Presented •Yune ¾, 1955, New York City IT Is ^ mistake to think that the introduction of synthetic detergents into bar form is a recent innovation. Experiments along these lines have been carried out over a quarter of a century. The fact that during most of these years they met only limited success under special conditions indicates the enormity of the problem. The initial attack was to incorporate the detergent with binders and to frame and cut the product as a laundry bar. The salt water bar used by the Navy during World War II is an example. The use of synthetics in toilet bars made its appearance about a dozen * John W. McCutcheon, Inc., New York 17, N.Y.