Study on the Detection Methods and Usage of Permissible Colorants in Cosmetics

Study on the detection methods and use of permitted colorants in cosmetics
In today’s “face value era”, people are paying more and more attention to their appearance, and make-up has been accepted by more and more Chinese people as a kind of etiquette and the concept of image building. China’s color cosmetics market has taken shape and entered an accelerated stage of development. Colorants are mainly used in color cosmetics products, i.e. lipstick, rouge, eye shadow, mascara, nail polish, etc. Compared to the previous color cosmetics market structure, which was dominated by lipstick and rouge, the market share of mascara, eye shadow and nail polish is now growing rapidly. In recent years, by the impact and influence of the Internet idol, consumption upgrading and social tolerance, boys depicting eyebrows and lips are no longer condemned as a bad taste, men’s makeup products have become another new growth point in the cosmetics market, and the speed of development of the men’s makeup market should not be ignored. Other cosmetics such as shampoo, skin care creams, toothpaste, etc., although not belonging to the color cosmetics, but many also applied coloring agents, in order to enhance the commercial value of the product with the appropriate color, to arouse the consumer’s desire to buy. In view of this, it is necessary to study and analyze the testing methods and use of permitted colorants in existing cosmetics.
1 Types of permitted colorants and safety risks

Colorants in cosmetics are substances that use the principle of absorbing or reflecting visible light to give color to cosmetics, the body or parts thereof, and their role in products is mainly evaluated from the perspective of cosmetic coloring and psychology, with no other benefit to the human body. Many colorants can also be used as hair dyes or eyebrow tinting products. For example, acid dyes can be used to dye hair directly by passing through the surface portion of the hair and entering into the hair texture, without the need for an oxidation reaction as in the case of oxidative hair dyes, which can be used to dye the hair into a variety of different shades. Therefore, this type of hair colorant is relatively less irritating, less likely to damage hair and cause allergies, but the disadvantage is that the color firmness is poor.

Colorants can be classified according to solubility: 1) substances insoluble in water or organic solvents and other media, which are granular in the medium and can be dispersed uniformly; 2) water-soluble colorants, mostly containing hydrophilic groups such as carboxyl or sulfonic acid groups, which are sensitive to pH and ultraviolet rays, and can be easily oxidized or reduced, such as Food Red 17, Food Yellow 4, Acid Orange 7, etc.; 3) fat-soluble colorants, which usually don’t contain hydrophilic groups, and can be used for lipstick and other wax-based cosmetics, such as solvent yellow 33 and so on. According to the mode of origin, colorants can also be divided into two categories: natural and synthetic. Organic synthetic colorants are widely used in lipstick, rouge, nail polish and other cosmetics due to their strong covering power and coloring power, but many synthetic colorants come from coal tar products, which are azo compounds with certain safety risks, photosensitive reactions, reproductive development toxicity, and even a few may induce cancer. For example, pigment red 3 is included in the list of group III carcinogens published on October 27, 2017 by the International Agency for Research on Cancer of the World Health Organization.
Therefore the safety of colorant ingredients has been increasingly emphasized by consumers and regulatory authorities, and countries have conducted risk assessments and made corresponding regulations and restrictions, such as the Cosmetics Regulation (EC) 1223/2009 of the European Parliament and of the Council of the European Union, and Title 21 of the U.S. Code of Federal Regulations. Table 6 of China’s Safety Technical Code for Cosmetics (2015 edition) lists 157 colorants permitted for use and specifies their scope of use (various cosmetics, cosmetics other than eye cosmetics, cosmetics dedicated to non-mucous membrane contact, cosmetics dedicated to only temporary contact with the skin), other restrictions and requirements, and labeling provisions. For example, Acid Yellow 73 is limited to 6% in cosmetics, but it is prohibited for use in hair coloring products, and the content of the impurity resorcinol shall not exceed 0.5%, the content of phthalic acid shall not exceed 1%, and the content of 2-(2,4-dihydroxybenzoyl) benzoic acid shall not exceed 0.5%; and pigment red 3 and bromothymol blue can be used in cosmetics with

temporary contact with the skin only. etc. Nowadays, allergic problems caused by cosmetic colorants are fewer than before, mainly because the purity and safety of the colorants used in the products have been improved, and many cosmetic manufacturers, in order to respond to the consumers’ doubts about the safety of the colorants, have chosen food colorants among the permitted colorants, such as food yellow 3 (sunset yellow), food red 9 (amaranthine red), food yellow 4 (lemon yellow), food blue 2 (leucocyanine blue) , reducing blue 1 (indigo), pigment white 6 (titanium dioxide), etc.. However, the current national and local supervision and sampling of color cosmetics mainly focuses on heavy metal indicators and pays less attention to the use of colorants, and there is a certain gap in the supervision of colorants in cosmetics.
2 Detection standards and methods of colorants for permitted use

In view of the fact that some colorants are harmful to human health, the research on the detection methods of colorants in cosmetics has been paid more and more attention in recent years, and there are quite a number of detection methods reported in the standards and literature, mainly high performance liquid chromatography and liquid chromatography-mass spectrometry, etc. Other methods, such as micellar electrokinetic chromatography, thin-layer chromatography, and ultraviolet spectrophotometric method, have been basically eliminated due to the high limit of detection and the poor specificity. There are not many foreign inspection standards for hair coloring products, mainly South Korea’s “Cosmetic Colorants Types, Standards and Test Methods”, etc., but most of the methods are to determine one or two substances individually, and there are not many colorants that can be detected at the same time. China has established several standards for colorant testing methods, covering about 1/3 of the permitted colorants, including GB/T 30938-2014 “Determination of Food Orange 8 in Cosmetics High Performance Liquid Chromatography”; GB/T 37545-2019 “Determination of 38 Permitted Colorants in Cosmetics High Performance Liquid Chromatography”; SN/T 2105-2008 “Determination of water-soluble pigments such as lemon yellow and orange yellow in cosmetics”; SN/T 2448-2010 “Determination of water-soluble colorants in lipstick by high performance liquid chromatography”; SN/T 4575-2016 “Export of Determination of Various Banned and Restricted Colorants in Cosmetics by High Performance Liquid Chromatography and Liquid Chromatography-Tandem Mass Spectrometry”; DB44/T 961-2011 “Determination of Acid Orange 7 in Cosmetics by High Performance Liquid Chromatography”; DB35/T 1338-2013 “Test Method for the Contents of Natural Red 4 in Cosmetics”; “Cosmetics Safety Technical Specification for Cosmetics (2015 edition), “High Performance Liquid Chromatography for Alkaline Orange 31 and 7 other substances” and “High Performance Liquid Chromatography for Colorant CI 59040 and 10 other substances”. In addition, titanium dioxide, which can be used as both a colorant and a sunscreen agent, has a test standard SN/T 1478-2004 “Detection Method of Titanium Dioxide Content in Cosmetics ICP-AES Method”, and there are also methods for the determination of titanium dioxide and silver in the “Technical Specification for the Safety of Cosmetics” (2015 Edition). The permitted colorants involved in the above standards are shown in Table 1.
Table 1 Permitted colorants involved in Chinese testing standards

As the process of standardization is more standardized, the determination methods have been verified by several units, with good specificity, precision and reproducibility, therefore, testing organizations and cosmetic-related enterprises generally give priority to the use of standard methods when testing colorants in products. Only for those that are not in the standards will they consider establishing their own determination methods or referring to the methods reported in the literature. The colorants not covered in the above standards reported in the literature in recent years are shown in Table 2. The literature method is an effective supplement to the standard method, and is also the basis for the development of many standards.
Table 2 Permitted colorants covered in the literature
In the standards and the literature, the detection of colorants by high performance liquid chromatography (HPLC) is the most common. Pre-treatment according to the solubility of the components to be tested will be extracted with water or organic solvents (methanol, tetrahydrofuran, trichloromethanol, etc.) ultrasonic extraction, and then centrifuged to take the supernatant filtration membrane, the use of solid-phase extraction and other means of purification is not much; for the lipstick and other difficult to extract the samples, you can use a water bath with heating (eg, GB/T 37545-2019), and for the homogeneous dispersion of some of the viscous larger samples, then you can add the anhydrous sodium sulfate grinding. The chromatographic conditions are usually ammonium acetate-acetonitrile or methanol as the mobile phase, and the detection wavelength is generally selected from 240 to 620 nm depending on the colorant, and the retention time and the spectral waveforms obtained by the diode array detector are used for qualitative characterization at the same time, and quantitative characterization is performed by the peak area. In addition, the adsorption effect of the filter membrane material on the colorants needs to be considered in the detection, for example, hydrophilic groups such as amino and imino groups in the molecular structure of nylon can adsorb acidic dyes, while organic membranes such as polytetrafluoroethylene and polypropylene do not have much effect on the results. Some acidic colorants may be ionic in solution and poorly retained on reversed-phase columns, and the chromatographic separation can be improved by using tetrabutylammonium hydroxide and other plasma pairs of reagents.
Although the price of liquid chromatograph is moderate, and the laboratories of inspection organizations and large cosmetic enterprises are basically equipped with it, and the popularity of the related determination method is better, but due to the complexity of cosmetic matrices in general, the background interference of chromatographic peaks is more, resulting in the method for the separation of some structural and properties of similar substances can not be separated well, and the results of the test may produce some deviations. Therefore, future research should focus on sample pretreatment and purification techniques to improve the specificity of the method and reduce the detection limit.
Compared with liquid chromatography, liquid chromatography mass spectrometry can overcome the relative lack of specificity of the former, easy to have the shortcomings of false positives, and can shorten the analysis time of the sample, higher sensitivity, suitable for trace samples and complex matrix qualitative and quantitative analysis of cosmetics, and is also currently applied to the detection of colorants in the best comprehensive results of a method, the shortcomings of the detection equipment is relatively high price, generally only professional The disadvantage is that the price of testing equipment is relatively high, generally only professional testing organizations will be equipped, and enterprises will rarely have. Liquid chromatography mass spectrometry usually can detect more colorants at one time, with different structures and properties, in order to ensure the recovery of the method, a certain concentration of salt solution can be added to the extraction solvent to weaken or eliminate the electrostatic adsorption between the target compounds and the substrate.The pre-treatment method of SN/T 4575-2016, on the basis of this standard liquid chromatography method, uses the solid-phase extraction purification means, avoiding the problem of poor specificity of the solvent extraction method, but some cosmetics contain special components that are easy to block the extraction column, and need to pay attention to the use. In recent years, some literature [15,17,18] used a relatively novel matrix-dispersed solid-phase extraction, in which the sample was mixed with a desiccant (e.g., anhydrous sodium sulfate) and a dispersant (e.g., sand) and loaded into a solid-phase extraction cartridge containing C18 or Florisil powder, and then eluted with methanol. This method has the advantages of simple operation, short time-consumption and low consumption of organic solvent compared with the traditional pretreatment method of organic solvent extraction-solid phase extraction cleanup, and is expected to be more widely used in the future.
3 The use of permitted colorants in commercially available cosmetics
As the number of people wearing makeup continues to expand, the use of color cosmetics and the scale of production is increasing rapidly, and the colorants used in the products are abundant and diverse.
Chen Meng et al. investigated 69 commercially available makeup products, and detected a variety of permitted colorants, including pigment red 3, pigment red 48 and pigment red 49, in addition to solvent red 23, a banned substance in the Technical Code for Cosmetic Safety (2015 edition).
Guerra Eugenia et al. determined 24 cosmetic and personal care products available on the market, covering a wide range of lip, face and eye color cosmetics, shower gels, liquid soaps, shampoos and toothpastes. A total of five permitted colorant ingredients, including food yellow 3, food yellow 4, food blue 2, food red 17 and food red 1, were detected at levels ranging from 0.110 to 199 mg/kg. Among them, Food Yellow 4 and Food Red 17 had the highest detection rates, both of which were 11 times. More than half of the products contained two colorants, and two of them contained three colorants.Guerra Eugenia et al. additionally tested 14 cosmetic products, and the colorants detected included Food Red 7, Acid Orange 7, Food Yellow 3, Food Red 17, Food Yellow 4, Food Blue 2, and Acid Red 92, with levels ranging from 0.232 to 575 mg/kg.Among them, the detection rate of Food Blue 2 was the was the highest with 6 times, followed by Food Yellow 3 and Food Red 17 with 3 times each.
Ren Guojie et al. examined 101 coloring samples in the market and found that in terms of frequency of use, acid red 98, food yellow 3 and acid blue 9 were higher, followed by pigment red 49, food red 17 and acid violet 9. The study found that the amount of colorants detected in many products was small, and by analyzing some of the raw materials of the colorants, it was found that certain raw materials were of low purity, and thus it was hypothesized that these traces may have been due to the It is therefore hypothesized that these trace amounts of colorants may have been introduced due to the impurity of the raw materials used. The impurity of colorant raw materials can easily lead to unconscious misuse or wrong use by manufacturers, which may cause unnecessary safety hazards to consumers. Therefore, the regulation of colorant raw materials and the analysis and testing of their products should be strengthened in the future.
Zhang Fenglan et al. detected 27 kinds of permitted colorants in eyebrow dyeing products, including pigment black 11, pigment red 101, 102, pigment yellow 42, 43, pigment white 6, food blue 2, pigment white 20, etc. The products were mainly added with 3~5 kinds of colorants, among which the ones containing 4 kinds of colorants were the most, amounting to 56.6%; those containing 5 kinds of colorants accounted for 17.3%; and those containing 3 kinds of colorants accounted for 15.6%. A series of iron oxide compounds are used most frequently, pigment black 11 (ferrous oxide + iron oxide) reaches 92.2%; followed by pigment red 101, 102 (iron oxide) and pigment yellow 42, 43 (hydroxyl iron oxide), which account for 90.5% and 89.6% respectively; and then titanium dioxide, which is the strongest covering ability among white pigments. Although the total number of colorants used amounted to 27, the colorants with high usage rates were relatively concentrated, with most of them being used less than 3.0% of the time.
In addition, some literature points out that there are cases in which the colorants detected in the samples are inconsistent with the identification in the ingredient list of the products, such as food yellow 3 and acid orange 7 detected in a cosmetic product, but only one of the compounds is identified in its ingredient list, which is not an isolated case. On the surface of the problem is only labeling, in essence, reflects the enterprise management is not standardized, not in place, quality awareness is not strong, product formula even if the changes are very small, can not be afraid of the trouble or cost savings and do not go to replace the label and re-formulation of the record or approval.
To sum up, more coloring agents that can also be used as food coloring, such as Food Yellow 3 (Sunset Yellow) and Food Red 17 (Seduction Red), are currently used in color cosmetics products, which is conducive to cosmetic companies to prove the safety of their products to consumers. Eyebrow- and hair-dyeing products differ in their application of colorants due to the large differences in the targets and requirements of ordinary cosmetics, with iron oxide compounds being used most frequently.
4 Conclusion
China’s cosmetic market had total sales of 250 billion yuan in 2018, with an average annual growth rate of about 10%. Although the domestic color cosmetics industry started late, with the progress of the times, the national thinking is slowly changing, accompanied by the generalization and rejuvenation of the color cosmetics market and the opening up of the male color cosmetics market, the use of the population is becoming more and more widespread, and in recent years, it has ushered in the maturity of large-scale development. Therefore, improving the quality of color cosmetics is conducive to safeguarding the safety of consumers and promoting the healthy development of the industry. However, the permitted colorants covered by the current standard only account for 1/3 of the Technical Code for Cosmetic Safety (2015 edition), and with less than half of the detection methods reported in the literature, there are still many gaps in the determination technology of colorants. At this stage, priority should be given to transforming the testing methods in the literature into standards, especially pigment red 3, solvent violet 13, pigment yellow 3, solvent orange 1 and bromothymol blue and other colorants with a restricted scope of use, in order to gradually improve the formulation of colorants.