456 JOURNAL OF COSMETIC SCIENCE Carbon Black. Carbon black is the most commonly used black pigment (46). Carbon black is pure ele- mental carbon produced by the partial combustion or thermal decomposition of gaseous or liquid hydrocarbons (42). Black pigments adsorb all wavelengths of visible light, and carbon black adsorbs up to 99.8% of visible light (42). The most important characteristic of carbon black is the small particle size and highly developed surface area of its particles, which gives it a high adsorption capacity. The tinting strength of carbon black is known to be determined chiefly by the particle size (51). As the properties of carbon black align more with those of typical or general inorganic pigments than those of organic pigments (52), carbon black is considered an inorganic pigment in this report. Polycyclic aromatic hydrocarbons (PAHs) have been found to be adsorbed onto the surface of carbon black during manufacturing processes, and all four entities have established content limits for PAHs in the pigment (Table VIII) Carbon black consists of 95% pure carbon and other impurities adsorbed on the surface. The primary particle size of carbon black is between 5 and 500 nm, and those of its aggregates and agglomerates are 100–800 nm (53). To use carbon black as a pigment in the EU, the pri- mary particle size must be greater than or equal to 20 nm, according to Annex VI (entry 126a). In the United States, carbon black is not exempt from certification, and the correct INCI name for carbon black after it has been certified by the FDA is D&C Black No. 2. In summary, an inorganic pigment is a ground fine mineral powder with chemically inert and insoluble properties. The use of inorganic pigments dates back to ancient times. Still, there is a steadily increasing demand for inorganic pigments because of their low cost, stability, and lack of toxicity. In many countries, the heavy metal content in cosmetic colorants is strictly regulated. However, the variety and content of each heavy metal allowed may vary from country to country. In addition, uniform standards on pearlescent pigments that are widely used in the cosmetic industry are required. Table VIII Comparison of Purity Specifications of Carbon Black Purity Specification EU United States China Korea Name CI 77266 D&C Black No. 2 CI 77266 Carbon black Ash 4.0% 0.15% Limit for polycyclic aromatic hydrocarbons: for 1g of Colorant samples, 10g of Cyclohexane is added, after continuous extraction in the extractor, the extraction liquid should be colorless, whose fluorescent intensity under ultraviolet rays shall not exceed that of control solution of quinine sulfate(0.1mg quinine sulfate dissolve in 1000mL 0.01mol/L sulfuric acid solution) Arsenic 3 mg/kg 3 mg/kg 3ppm Lead 2 mg/kg 10 mg/kg 10ppm Mercury 1 mg/kg 1 mg/kg Cadmium 1 mg/kg Total Sulfur 0.65% 0.65% PAH Benzo[a]pyrene Dibenz[a,h]anthracene 50 μg/kg 0.5 mg/kg 0.005 mg/kg 0.005 mg/kg 0.5ppm 5ppb 5ppb Alkali soluble matter Colorless Assay 95% 95% 95.0% EU: European Union. “—”: does not have a criteria.
457 COSMETIC COLORATION: A REVIEW NATURAL COLORANTS Recently, the “clean beauty” trend has become increasingly popular in cosmetic markets around the world. The term “clean beauty” has no legal definition right now. Generally, it means a beauty product’s manufacturer should consider human and environmental health, using nontoxic ingredients as a baseline and natural ingredients for active results (54). Clean beauty advocates natural products containing ingredients from plants and nature. Keeping pace with this trend, consumer demand is increasing for natural colo- rants instead of synthetic colorants. In this report, natural colorants are colorants derived from natural sources. However, there is no widely accepted definition of natural colorants, and the term “natural colo- rant” is not used in four entities as it could mislead consumers. In this report, colorants from a natural origin (e.g., plants and insects) that are included on the positive lists in the regulations of each country (excluding the inorganic pigments discussed previously) are grouped as natural colorants regardless of their manufacturing process. Natural colorants can be classified based on their chemical structures (e.g., carotenoid, quinonoid, and fla- vonoid) and origin (e.g., plants and insects). Unlike synthetic colorants, natural colorants are expensive and easily affected by external factors such as pH, oxygen, heat, and light. In an effort to improve the stability of natural colorants, optimal extraction conditions and techniques for encapsulation matrices have been widely studied. While synthetic colorants are tightly regulated because of their historical risks, natural colorants are defined ambiguously and relatively loosely, as currently regulated. For natu- ral colorants, the specifications focus on a general test for residual solvents, an assay, and a test for heavy metals as these colorants are obtained mainly from plants. As the geographic origin and climate substantially influence their quality, the acceptance criteria of the assay test is relatively lower than those of synthetic colorants. There are no generally agreed upon maximum levels and types of residual solvents and heavy metals for natural colorants in cosmetic products. For instance, in the process of annatto extraction, isopropyl alcohol is allowed as an extraction solvent in the United States and Korea but not in the EU. In addition, the acceptable residual concentration of acetone varies from the United States and Korea ( 30 ppm) to the EU ( 50 ppm). The rest of this article encompasses general definitions, a comparison of regulatory requirements, and the practical limitations of natu- ral colorants. As China has not established the specifications for natural colorants, this sec- tion will focus on the regulatory differences between the EU, the United States, and Korea. Carotenoids: Annatto, Lycopene, ß-Carotene, and Paprika Extract. Carotenoids occur naturally in plants, algae, and fungi. There are over 600 known carot- enoids. Carotenoids used in cosmetics are annatto, lycopene, β-carotene, and paprika extract. They exhibit different colors: red, orange, purple, and yellow. Carotenoids are categorized into two types: xanthophylls and carotenes. Xanthophylls contain hydro- carbon and oxygen (e.g., lutein, zeaxanthin, and astaxanthin), and carotenes contains hydrocarbon without the oxygen (e.g., α-carotene, β-carotene, γ-carotene, and lycopene) (55). Carotenoids typically contain eight isoprene units (Figure 8) (56). There have been reports of stability problems in carotenoids because of their extensive conjugated double bonds, which are referred to as the polyene chain (57–61). An unsaturated carotenoid is susceptible to oxidation and isomerization. The mechanism of carotenoid oxidation
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