30 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS dize rapidly, the thicker application serves as a protection from oxidation by the air while the mercaptan is acting at the level of the skin. Also, because the free liquid content of the cream is low, the danger of irritating the follicle is obviated. The choice of fillers or cream-forming materials is much wider with mercaptans than with sulfide depilatories. 6. Because the substituted mer- captans produce depilatories that are substantially non-odorous, one is likely to overlook that they have solved one of the most troublesome problems associated with sulfide depilatories, namely, that of perfum- ing the product. As stated by Koeune, this is not merely a matter of covering the odor of the depila- tory but of finding aromatic ma- terials which will not be destroyed or changed into foul-smelling com- pounds by the ingredients of the depilatory. With the mercaptan depilatories we have found that a much wider choice of perfume ma- terials is possible not only because lighter fragrant types may be used but also because many perfume ma- terials destroyed or changed by sulfide depilatories remain un- changed in mercaptan depilatories. 7. The mercaptan depilatories are less irritating than the sulfide depilatories. On this point our original findings have been con- firmed by 6thers. For example, Consumers Union reported(8) that thioglycolate depilatories "are some- what milder in their action than the sulfide depilatories and medical authorities believe that they are less likely to cause dermatitis than the sulfides." During an epidemic of ringworm in Hagerstown, Maryland, when a commercial thioglycolate depilatory was applied to even the infected areas on a large group of school children for the removal of hair, there were no unfavorable results. The thioglycolate depilatories were first offered to the American public in June, 1939, and although the war has hampered their exploi- tation, nevertheless, it is estimated that this year the sales of cosmetic depilatories will be approximately three times the sales of any previous year, and more than ten times the amount sold in •938. The mercap- tan depilatories will be the reason for that advance. MERCAPTANS IN COLD WAVING The depilatory market, though, cannot even approach that of cold waving, because the income from this source is derived not only from sales of the product for use at home but also from the huge amounts of the product used in the beauty shop. Within the short period of five years cold permanent waving has become the preferred method of permanent wavi-ng of the women of America. Today over 50% of all permanent waving is done by the cold process, and it has been esti- mated that between 25,000,000 and 30,000,000 permanent waves will be given professionally by the cold waving process during •946. Permanent waving accounts for approximately 60% of the income

MERCAPTANS IN COSMETICS 31 of a beauty shop, and cold waving alone accounts for over 30% of the shop's income. As the total yearly income of the beauty shops of America is estimated to be one billion dollars, cold waving not only becomes the most significant source of income for the 300,000 beauty operators but also plays an impor- tant role in our national economic structure. All of this commercial revolution has happened since the spring of 1941. After the unfortunate death of an Atlanta matron who had just had a cold wave, the Federal Government effectively halted all cold waving by the seizure of the cold wave lotions. These, however, contained ammonium hydrogen sul- fide, which was the only chemical agent then used commercially to wave hair at low temperature in a short period of time. One large chain of beauty salons which had spent a small fortune in ventilating equipment to dispose of the toxic and malodorous hydrogen sulfide gas was the first to utilize commercially a cold wave lotion con- taining mercaptan as the successful displacement for the noxious sulfide lotions. Thus at one stroke the poison, bad odor, and cumbersome equipment associated with the use of the sulfide lotions were displaced by the mercaptan lotions which are superior in every respect. The cold wave product introduced by this group of salons was an earlier discovery made as a result of exten- sive research and development in our laboratory. The principle is that mercaptans, particularly in an alkaline medium, were effective waving agents and could be used for waving at low temperature. With- out going into the details of these experiments, some of the conclu- sions reached were as follows: The substituted mercaptans were not only more effective but also preferable because in the proper medium they gave less odor. The concentration of the mercaptan was less than 15% and preferably was in the range of 2% to 10%. In cold waving with mercaptans the range of pH is very important. Although below pH 7 cold perma- nent waving is possible, the time re- quired is very long. No critical difference in time is noted below pH 7. At this pH there is a break, for at this point the time to 'wave sharply decreases with even a slight increase in pH. The critical upper limit for pH is 10, because at this pH and above, the hair is seriously damaged before it can be waved satisfactorily. A particularly critical range of pH is from 9.2 to 9.5. Within this range the hair can be waved quickly without being damaged therefore, this range is to be preferred for com- mercial use especially in beauty shops. Although many alkaline com- pounds may be used, the bases hav- ing a dissociation constant less than 5 X 10 -3 give the best results. The volatile bases are particularly effective for example, ammonia and ethylamine are preferable to the non-volatile monoethanolamine.