HAIR COLORING--MODERN FORMULATION CONSIDERATIONS 297 There is a second reason why such hair takes up more dye. Not only are more of the usual dye sites accessible due to the swelling, but the su./fhydry/ group of cystei,e provides a new type of dye site. Cysteine will react with sulfonic acid dyes to such an extent that it is possible to re-crosslink reduced hair by use of disulfonated colors. They can take the place of the usual oxidizing bath. Several years ago, the author helped formulate a permanent dye based on this principle, using disulfonated U.S. certified dyes in combination with an alkaline thioglycolate. Tensile strength measurements showed that it was not necessary to follow this treatment with the usual oxidizing step since the hair was substantially cross linked by the dyes. The British chemist Deadman also came to the same general conclusions, receiving a patent (31) in 1955 as a result of his work. D,zEs UsEr •s HAIP. COLOP.•N'G Metallic Dyes. The deliberate application of lead and other heavy metal salts to the hair has been practiced for several thousand years. Currently known as "progressive dyes" due to the slow additive manner in which the the color develops on repeated application, an "instant" version is also sometimes offered. In this version, there are two solutions the first (the "dye") containing the heavy metal salt, and the second (the developer) containing a sulfide or pyrogallol which produces a brown or black precipi- tate on the hair. One really modern version recently appeared with a thio- glycolate as the developer. In spite of their rather dubious toxicity and sometimes unnatural appearance on the hair, such products will always find a market since they are water-white liquids which do not look messy. In the field of hair dyes, this is a tremendous advantage. Fegetable Dyes. There is only one of commercial importance today (7), henna. Henna extracts are used alone, sometimes modified with pyrogallol or logwood, and sometimes mixed with acid dyes. Safe and nonirritating, henna gives colorfast dyeings which have a rather unsubtle look on repeated application. Oxidation Dyes. These constitute the major type of colorant used in the United States for permanent hair dyeing. They include the aromatic amines (the para dyes) and polyhydric phenols such as resorcinol and pyro- gallol. Harry (8) gives an excellent concise review of these oxidation colors. Kass gave a longer one in a series of articles (12) which appeared a few years ago. These dyes are unique in one notable respect--the use of peroxide required to form the final color pigment. This allows "lightening" at the same time as dyeing, but also requires a two-bottle product which must be used shortly after mixing. The hair damage occasionally caused by such dyes is due to the combination of peroxide and alkaline conditions. Unfortunately, questions of toxicity, skin irritation, sensitization and eye damage caused by the oxidation dyes seem to have become rather academic

293 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in this country. They are still of considerable interest to state and federal regulatory agencies and to the chemist, but the ultimate user seems to ig- nore the whole matter. The legally required warning label has apparently become such a common sight to the consumer that only those persons who know they are sensitive to such products pay any attention to it. Several advertising campaigns based on the safety aspect of products containing only certified dyes have fallen rather flat. /lcid Dyes. These are the principal type used in temporary hair color- ings. Many of the U. $. certified colors are acid (anionic) dyes their use presents the manufacturer certain advantages. He has the assurance that exacting quality control was maintained during their manufacture and has less fear that his product will cause allergic reaction. Although it seems that this safety angle does not have much advertising value, these "dyes with a pedigree" (13) give the manufacturer one tremendous advan- tage in a field noted for the nuisance lawsuit: they allow him to shift the onus for purity of active ingredient onto the federal government. There is a certain magic in the words, "Contains only government certified dyes," which tends to keep the customer honest, reducing get-rich-quick lawsuits to a minimum. Certified dyes commonly found in temporary hair colorings include the following: FDC Blue 1 DC Brown 1 Ext DC Green 1 Red 1 Black 1 Orange 3 Red 2 Violet 1 Red 11 Yellow 5 Red 37 Red 13 Yellow 10 Yellow 1 The main drawback to their use is the fact that no certified color will give a usable brown or black by itself, forcing the formulatot to work with mix- tures of primary colors which sometimes take quite differently on damaged hair than on normal hair. Trying to balance out such effects results in shade mixtures of five or six dyes which are difficult to control in production. Temporary hair colorings also often use uncertified acid dyes such as nigrosine, which has a long history of safe use over the past thirtv to forty years. Such harmless uncertified dyes may be used in hair products with- out including the caution statement on the label. However, the Food, Drug and Cosmetic Act states that the manufacturer who elects to do so assumes all responsibility should it be found that the colors used were in fact dangerous. Basic Dyes. Two of these (methylene blue and rhodamine) appear on the certified list, and many other uncertified ones such as safranine, Bismark brown, chrysoidine, methyl violet and thiofiavine have been used in hai• colorings. They are generally restricted to temporary tints because of their poor light fastness. They give very strong coloration on the hair, and