258 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS be extracted with a fat so]vent in order to free the enzyme create the greatest concern. One example of such a problem is the inability to dis- tinguish between poor recovery due to poor stability, or due to the tech- nique used to separate the water soluble protein from the lipophilic base. The proper selection of the type of ointment, as well as the components with which it is made, can spell the difference between being able to demon- strate both in vitro and in vivo activity and having a preparation with the enzyme so bound as to make it virtually useless. And finally, it should also be recognized that an enzyme can be chem- ically, as well as physically, complexed to some components of cosmetic preparations, due to the large number of reactive groups present on all proteins. An example of this particular type of problem is the complexing of certain types of enzymes with carboxymethylcellulose, which appears to occur via an ion exchange-type of mechanism. Sometimes reactions of this nature can be minimized by adjusting pH or preferentially complexing the proteins with reagents that will not interfere with the activity, or the physical stability, of a cosmetic preparation. C. AS'eas of •uestionable Potential The cosmetic chemist most certainly will become better acquainted with the desirable features of enzymes that make them so suitable for cosmetic purposes. This does not mean that enzymes will become the panacea there are many areas in which nonenzymatic methods are, and will remain, superior. For example, it would take a most remarkable enzyme to function as a cuticle remover as effectively as do the inorganic alkalies currently in use. Also, as indicated above, an enzyme with the characteristics of the "ideal" depilatory more than likely does not exist. The areas of most questionable potential are those in which the demand is for an agent to react instantaneously on an insoluble substrate. The critical parameter as far as the enzymes are concerned is the insoluble substrate with which the cosmetic chemist is so often concerned. Under the proper conditions enzymes can perform in the desirable fashion, if the substrate is readily available. Unfortunately, many of the conditions with which the cosmetic chemist must deal are those that are least compatible with the requirements of the enzymes. However, by adjusting some of these, such as the extension of contact time, choice of suitable dosage form, etc., some of the drawbacks can be overcome. In those areas where nonenzymatic reagents may be more economical and function as well as or better than their enzymatic counterparts, it would be pointless to consider an enzyme as the active ingredient. How- ever, there are areas in which enzyme specificity would offer such ad- vantages (e.g., in cases of "oily skin" it may be possible to remove specific

POTENTIAL OF ENZYMES FOR TOPICAL APPLICATION 259 portions of sebum which would otherwise be completely removed with fat solvents) that the development of such products would be well worth the added effort. IV. SUMMARY Whether or not an enzyme can be used for a given topical application depends on the nature of the cutaneous disorder as well as the limitations associated with the enzyme activity. To a large extent, the physiology and anatomy of the skin dictate the degree of success an enzyme prepara- tion might enjoy as a cosmetic or therapeutic agent. (The distinction between "cosmetic" and "therapeutic" has become extremely difficult to define and is in all probability more a question of semantics than of practical importance.) The enzyme group that has proved to be quite useful is the proteases, some of which have more suitable specificities than others. In addition, the search by suppliers for new enzymes active on the more refractory substrates continues. Recent studies of enzyme formulations suitable for topical use have shown that such dosage forms are relatively easy to handle. However, the choice of base, surface active agent, etc., is important to provide for a stable formulation. The choice of base is also important in determining the ease with which the enzyme present can be assayed. Since enzymes can act only in an aqueous environment, proper vehicle selection is also critical for the proper activity in silu. The mild conditions associated with the enzymatic process, dovetailed with the characteristics of healthy and pathological skin, provide for op- timism as far as the potential of enzymes for topical application is con- cerned. While all of the requirements of the cosmetic chemist cannot be met with currently available products, enzyme research and development is being conducted with these in mind. (Received February 8, 1963) REFERENCES (1) F. Haurowitz, Chemistry and Biology of Proteins, Academic Press, Inc., New York (1950). (2) W. H. Ward and H. P. Lundgren, Atdvances in Protein Chemistry, IX, Academic Press Inc., New York (1954). (3) Drug Topics, 106, July 16 (1962). (4) D. G. Welton, Skin Dermatol. in Practice, 4, 131 (1962). (5) R. G. Harry, Cosmetics: Their Principles and Practices, Chemical Publishing Co., New York (1956). (6) D. M. Pillsbury, et al., At Manual of Cutaneous Medicine, W. B. Saunders Co., Phil- adelphia (1961). (7) S. Rothman, Physiology and Biochemistry of the Skin, University of Chicago Press, Chicago (1954), p. 300. (8) H. W. Siemens, General Diagr. osis and Therapy of Skin Diseases, University of Chicago Press, Chicago (1958), p. 53. (9) D. R. Goddard and L. Michaelis, 5'. Biol. Chem., 106, 605 (1934). (10) D. R. Goddard and L. Michaelis, Ibid., 112, 361 (1935). (11) D. J. Millin and M. H. Smith, Nature, 189, 664 (1961).