RESINS AND THEIR APPLICATION TO DRUG AND COSMETIC PRODUCTS 293 Since ion exchange resins are insoluble but exhibit reactivity of their fuvctional groups when hydrated and placed in contact with an electrolyte- containing environment, they retain their original identity when mixed in a powder, lotion or hydrophilic ointment. By an ionic binding reaction, they serve as a means of absorbing and rendering inactive certain undesirable skin irritants or exudant products of a skin eruption. For topical applications, bead form ion exchange resins are purified to remove residual traces of unreacted low molecular weight hydrocarbons and metallic contaminants and then are ground to an impalpable powder of Figure 1.--Microphotograph of a bead form, strongly acidic, sulfonic type, cation exchange resin. an average particle size of 25 mi- crons. These powders, when prop- erly formulated, are nonirritating and cosmetically acceptable for ex- ternal use, even on tender and sensi- tive skin. The ion exchange activity provided by these resins prevents or inhibits the growth or reproduction of organisms, including both fungi and bacteria, which are sensitive to the pH character of the resin or the therapeutic ionic salt form of the resin. Moreover, the resin is cap- able of absorbing and rendering in- active metabolic products, toxins, or decomposition products resulting from the growth of organisms. The specific ion exchange resin sys- tems which have received major at- tention in dermatological prepara- tions are Amberlite XE-64, a weakly acidic, carboxylic acid type, cation exchange resin, notable for its ability to control pH and absorb basic skin toxins the cobalt salt of Amberlite XE-64, which provides a nonirritating sustained release source of cobalt which has marked bacteriostatic and fungistatic action and Amberlite XE-87, a four-component cation and anion exchange resin system which provides an absorption mechanism coupled with controlled buffering action. PRINCIPLES OF ACTION The ability of an ion exchange resin to retain its identity in a dermatolog- ical system because of its insoluble nature and its reactivity with skin elec- trolytes or ionic skin irritants provide a dual role in its action. Therapeutic formulations can be developed for the correction of an imbalance of electrolytes on the skin surface. The reactivity of these systems can also

294 JOURNAL OF THE SOCIETY OF-COSMETIC CHEMISTS "•T-•"•.•%T•'L." d,.. ••• .••. /• . ,o R o. N• •N 0 OH Figure 2.•Sketch of cation exchange resin Figure 3. Sketch of anion exchange resin particle in hydrogen form. particle in hydroxyl form. be used to provide protection against skin invasion by bacteria and fungi as well as organic or inorganic materials which bring about an undesirable alteration in skin pH, thereby permitting use in "preventive maintenance" procedures. THERAPEUTIC A. pH Contro/•mberli•e XE-6• •eak/y •cidic, Carboxylic Type, Cation Exchange Resin Thurmon (13, 14) has shown that a single resin component of the car- boxylic acid type when incorporated in a powder, ointment or lotion adjusts or maintains a desired, mild, acid mantle on the skin. When the skin is broken or irritated, it is common for the damaged area to develop al- kalinity. In some cases, skin surfaces become alkaline from the con- AMBERLITE 1•'12 T AMBERLITE CAR80XYLICTYPEL•CHAN•R, ---'-'"""'"• R. + CAPACITY IN MILLIEOU•VALENT$ PER GRAM Figure 4.--Comparison ooe titration curves for suloeonic (IR-]20) and carboxylic (IRC-50) cation exchange resins. I I I I 4o 0 l, H TiTRATiO N IN 1 • KCL SOLUTION. AMBERLITE IR _•'"• • CAPACITY IN M[LLIEOUIVALENT$ Pt8 GRAM Figure 5.--Comparison of titration curves for weak base (IR-4B) and strong base (IRA-400) type anion exchange resins.