452 JOURNAL OF COSMETIC SCIENCE they need clarification of the specific substitution sites for mono- and disulfonates (e.g., 6’4-disulfonate, 8’,5-disulfonate). QY is a bright yellow dye with a green shade. It is prepared by condensing quinaldine 7 with phthalic anhydride 4, then sulfonating 2-(2-quinolyl)-1,3-indandione 8 (Figure 6) (37,38). The proportion of mono-, di-, and trisulfonated compounds varies considerably according to the extent of sulfonation (37–39). The definition of this colorant is significantly different between the EU and the United States. In the United States, the colorant has to contain more than 75% of the monosul- fonate, whereas in the EU, it has to contain more than 80% of the disulfonate (Table V). Therefore, when QY is permitted by the US standard, it is banned in the EU and vice versa. In the EU, oversulfonated products, trisulfonate, must be less than 7%. Particularly in the United States, the overall content of disulfonates should be below 15%, and 6’, 8’- indisulfonates below 3%. In Korea, Yellow 203 is defined as a mixture of mono- and N O O O ZnCl 2 N H O O i) H 2 SO 4 ii) NaOH N H O O Quinaldine, 7 Phthalic anhydride, 4 2-(2-Quinolyl)-1,3-indandione, 8 Quinoline Yellow WS (SO3Na)n n=1-3 Figure 6. Synthesis of Quinoline Yellow WS. Table V Comparison of Purity Dye Content of Quinoline Yellow WS Purity Specification EU United States China Korea Name CI 47005 D&C Yellow No. 10 CI 47005 Yellow 203 Pure dye content ≥ 70% ≥ 85% — (85.0–101.0)% Monosulfonated quinophthalone 2-(2-quinolyl) indan-1,3- dione- monosulfonates [sodium salts of the monosulfonates of 2-(2-quinolinyl)-1H- indene-1,3 (2H)-dione] ≤ 15% ≥ 75% — — Disulfoanted quiophthalone 2-(2-quinolyl) indan-1,3- dione- disulfonates (sodium salts of the disulfonates of 2-[2-quinolinyl]-1H- indene-1,3 [2H]-dione) ≥ 80% ≤ 15% — — 6′,8′-Disulfonated quinophthalone 2-(2,3-dihydro-1,3-dioxo-1H-indene- 2-yl)-6, 8-quinoline disulfonic acid, disodium salt — ≤ 3% — — Trisulfonated quinophthalone 2-(2-quinolyl) indan-1,3- dione- trisulfonate ≤ 7.0% — — — Abbreviation: ‘—’ : does not have a criteria EU: European Union. “—”′: does not have a criteria.

453 COSMETIC COLORATION: A REVIEW disulfonates more than 85.0% ~ 101.0%. Therefore, any colorants imported from the EU and United States can be used. In summary, we have discussed the general properties of synthetic colorants. It is import- ant to understand the structural features of colorants as their visual characteristics are easily affected. Synthetic colorants have intense and uniform color, high stability, and economical value. However, increased concern over misuse synthetic colorants led to the establishment of the regulatory system. After an assessment of each colorant, each country introduced its positive list of colorants, then established its impurity acceptance criteria as part of its specifications. These impurities may pose potential health treats when present in finished products. A comparative analysis of the colorant specifications of four entities was performed. The main regulatory challenges were that all countries have established their own sets of positive lists, specifications, and definitions of each colorant. The differences in regulatory systems may lead to misuse or confusion among consumers. INORGANIC COLORANTS Inorganic colorants have been used since ancient times, for example, ancient Egyptians used iron oxides extensively in tomb wall paintings (40). They are generally stable color- ing matters with a high heat stability, high chemical resistance, and low cost (41, 42). An inorganic colorant is defined as a dry, solid mineral that retains its color when ground to a fine powder (41). Inorganic colorants are chemically inert, insoluble compounds com- pared to organic colorants (42). They are classified as a pigment by definition because they are insoluble in the application medium. World production of colorants is estimated to 10,000,000 tons annually, about 80% of which are inorganic pigments (43). Titanium dioxide (66%), iron oxides (approx- imately 15%), and carbon black (approximately 10%) make up more than 90% of the pigments (44,45). Inorganic pigments are either produced naturally mined and synthetically manufactured (analogous to naturally occurring minerals). Specially, to provide stable color consistency and better strength, some inorganic pigments–such as iron oxides–are obtained by chemical routes rather than directly from the naturally occurring minerals. In the United States, colorants obtained primarily from mineral, plant, or animal sources are exempt from certification. Although they are exempt from certification, these colo- rants must conform to the identity, specification, restrictions, and labeling requirements in their individual listing regulations. Each country has its own positive list of inorganic pigments as well. For instance, mica is considered a colorant in the United States, but it is considered a general cosmetic ingredient rather than a colorant in the EU. The quality of inorganic pigments is also controlled through specifications. Heavy metal-based inorganic pigments such as lead, chromate, and cadmium pigments have limited or prohibited use in cosmetics. Other inorganic pigments may contain heavy metals a level that is not a threat to human health or the natural environment (46). In all four entities, the content of heavy metals (e.g., lead, arsenic, and mercury) in cosmetics is controlled by regulations. Titanium Dioxides. Titanium dioxide accounts for more than half of the worldwide use of inorganic pigments (45). Titanium dioxide is the whitest of all white pigments and is used extensively in the