Colorants Targeted for Further Government Scrutiny: Resorcinol and Solvent Red 23

Coloring agents have been around since ancient times, and there is no doubt consumers are heavily influenced by the color of a product. Colorants are often found in lipstick, makeup, nail polish, perfumes, hair dyes, soap, shampoos, creams and even mouthwash—the list is endless.

The most significant colorants in use belong to different chemical classes, including: azo compounds, triarylmethane, anthraquinone, xanthene and phthalocyanine.1 These organic colorants have been heavily scrutinized throughout history due to concerns about potential toxicity to humans and the environment. Several of the colorants in these groups have been banned or restricted by countries over time, and the list continues to grow. Formulators, manufacturers and consumers are interested to know the next compound to be added to the growing list of concerning colorants; some of the most recent developments regarding colorants are highlighted here.

Solvent Red 23

This colorant (CAS 85-86-9, CI 26100, D&C Red No. 17) has been on the radar of regulators in a number of countries with some new and important developments. In Canada, Health Canada’s Cosmetic Ingredient Hotlist is being revised to include the organic colorant solvent red 23.2 This ingredient can be found in hair grooming products, dyes, anti-wrinkle creams, shampoos, makeup, nail polish removers, tanning products, shaving creams, face paint and fragrances.3, 4

Solvent red 23 has been reviewed by the Canadian government and concluded to have genotoxic and carcinogenic health effects related to oral exposure.2 It is proposed that this ingredient will be prohibited in cosmetic products intended for use on or around mucosal membranes such as the eyes, nose and mouth.2 There will also be additional label warnings required for hair dyes containing this colorant, informing consumers to not use the product for eye lashes or brows, or around mucosal membranes.2

Health Canada’s proposal aligns nicely with the restrictions on this ingredient in the United States and the European Union, with minor differences. In the United States, the U.S. Food and Drug Administration (FDA) has additional certification requirements for solvent red 23.5, 6 In Europe, this ingredient has been under a microscope by the German government, where concerns are based on solvent red 23 being an azo dye that can form carcinogenic amines (e.g., 4-aminoazobenzene) upon metabolism in the gut.7 The Scientific Committee on Consumer Products (SCCP) concurs with the German government that solvent red 23 may pose an issue to consumer health, but does not have significant data to be conclusive.7 Despite Germany’s argument and SCCP's supporting opinion, this colorant still remains on the EU’s acceptable colorant list as long as certain purity requirements are met, and it is not used in products applied to mucous membranes.8

Believe it or not, regulation on solvent red 23 could expand beyond the federal level to certain states in the United States. For example, it could potentially fall under The Safer Consumer Products Regulation, as part of California’s Green Chemistry Initiative.9-11 California’s Department of Toxic Substances Control (DTSC) adopted these regulations to establish a process to identify and prioritize chemicals in consumer products (e.g., cosmetics) and to establish a process for evaluating chemicals of concern.9 DTSC released its “Initial” Candidate Chemicals List on Sept. 26, 2013, and it appears that most “aromatic azo compounds” such as solvent red 23 could be targeted for further assessment.11 After initial review, a subset of this list will be created and known as the “Priority Products list,” which is expected to be published in 2014-2015.9

If solvent red 23 (or any other colorant) becomes designated as a Chemical of Concern, products containing it will face a difficult challenge in California, in addition to the already complex Proposition 65 requirements.9, 12 Companies manufacturing such products will have to determine the best way to limit chemical exposure to humans and the environment;9 many might simply choose to reformulate.


Resorcinol is a fascinating multifunctional ingredient, mainly known for its hair coloring, antioxidant and anti-acne properties.13 This ingredient is already “hidden” on the Canadian hotlist under the coal tar dyes section and is prohibited for use around the eyes.2, 14 Health Canada is looking to extend this prohibition to use anywhere on the skin, but some hair applications will still be permitted.2

The EU has strict requirements for resorcinol as well. It can only be used as a coloring agent in hair dye (not for eye brows) at 5% w/w or less, and in hair lotions and shampoos at 0.5% w/w or less.8 The EU also requires several warnings on product labels containing resorcinol that are similar to Canada.

Surprisingly, the United States does not regulate resorcinol the same way as Canada or the EU. In the United States, resorcinol is considered an active ingredient that is commonly regulated for use in topical antimicrobial drug products, but there are no distinct regulations limiting amounts of resorcinol as a colorant in hair products or cosmetics.13, 15, 16 Countries are always trying to harmonize as much as possible, so there is a possibility that the United States could impose newer regulations on resorcinol used in cosmetics to align with Canada and the EU.

This regulatory burden on resorcinol may come as a shock to many, considering resorcinol has a history of safe use in multiple cosmetic products and is listed in the International Cosmetic Ingredient Dictionary and Handbook.13 A comprehensive safety assessment conducted by the American College of Toxicology tested the effects of 2-methyl resorcinol and resorcinol in non-clinical and clinical settings.17 No adverse events were observed following a dermal application of 5% and 10% resorcinol in a chronic dermal study.

In addition to this, resorcinol is rarely a sensitizer. In clinical testing, 5 of 250 and 1 of 149 patients exhibited irritation and sensitization to resorcinol. No sensitization to 15% resorcinol was reported in a study of 22 non-clinical subjects. The study concluded that although resorcinol is a mild skin irritant and a rare sensitizer in clinical testing, there was no application site irritation, sensitization or photosensitization when tested in cosmetic products on human volunteers. Researchers found it to be safe as a cosmetic ingredient in present practice of use.17

Sad to say, there are a few conflicting studies regarding resorcinol, which have been highlighted by many non-governmental organizations (NGOs) that put pressure on governments to respond, even if the scientific evidence is not conclusive.18-19 It is clear that resorcinol is a concern for many NGOs and governments, so despite many positive studies in support of resorcinol usage, it is considered a major target. Shock or no shock, resorcinol is an ingredient of concern in Canada and the EU, and the United States could jump on board at any time.

Solutions for Resorcinol and Solvent Red 23

One proactive solution is to reformulate by substituting resorcinol and solvent red 23 with ingredients that are already on approved regulatory lists with no restrictions. The formulator must ask themselves: Is this colorant necessary? and Is there a safer alternative? The FDA has a list of colorants accepted for use in cosmetics,6 and Europe has its own acceptable colorant list.8 California also has several additional lists for colorants worth reviewing, such as: Proposition 65, DTSC and the California Department of Public Health (CDPH) Chemicals List.11, 12, 20 In Canada, the hotlist contains colorants that are restricted or prohibited for use, which can be referenced when considering reformulation.

Another option for many is considering natural colorants. Consumers are becoming increasingly health-conscious and are looking for products with more natural components. Natural colorants do not seem to be a focus of regulatory scrutiny by governments right now, and most of these colorants are from vegetable sources, which some consumers prefer over synthetics. Examples of natural colorants include: anthocyanins from red berries, cartenoids from carrots and curcumim from turmeric.1 One caveat about natural colorants is they can exhibit a strong odor and are often considered inferior to synthetic colorants when it comes to resisting heat, light and pH differences. Therefore, R&D and stability testing is crucial when developing these types of products.1


The battle roars on, as worldwide government scrutiny continues with resorcinol and solvent red 23. Although these ingredients are still permitted in cosmetics under certain restricted uses, they are considered troublesome by most governments. Safer alternatives do exist for those willing to find them.

Consumers love a variety of colored cosmetics, so it is safe to say that color is here to stay. Formulators therefore must make sure that colored cosmetics are compliant with the latest colorant regulations.

1. AO Barel, M Paye and HI Maibach, Handbook of Cosmetic Science and Technology, New York, NY: Marcel Dekker Inc. (2001)
2. Proposed changes to the Cosmetics Ingredient Hotlist, Health Canada (Oct. 10, 2013)
3. Regulatory Impact Analysis Statement-Order Adding Toxic Substances to Schedule 1 to the Canadian Environmental Protection Act Part I, Canada Gazette 145(42) (2011)
4. Draft Screening Assessment, Aromatic Azo and Benzidine-based Substance Grouping, Certain Azo Solvent Dyes, Environment Canada, (Nov 2013)
5. Listing of Color Additives Subject To Certification, Part 74 of  Title 21, Food and Drugs, Chapter I- Food and Drug Administration Department of Health and Human Services, 21CFR74.1317 (Apr 1, 2003)
6. Color Additive Status List, FDA (2009),
7. Opinion on the use of CI 26100 (CI Solvent Red 23) as a colorant in cosmetic products, SCCP (2005),
8. Regulation (EC) No. 1223/2009, Official Journal of the European Union (2009)
9. What is the Safer Consumer Products (SCP) Program?, DTSC (2010)
10. What is the Candidate Chemicals list?, DTSC (2010)
11. "Initial" Candidate Chemicals List, DTSC. (2013)
12. Proposition 65, Office of Environmental Health Hazard Assessment (OEHHA) (2007)
13. International Cosmetic Ingredient Dictionary and Handbook (Dictionary), Personal Care Products Council (PCPC) (2013)
14. Cosmetic Ingredient Hotlist, March 2011, Health Canada, Consumer Product Safety Directorate (2011),
15. Understanding the Types and Dangers of Resorcinol in Hair Color, Organiccolorsystems (2012),
16. Topical Antimicrobial Drug Products For Over-The-Counter Human Use, Part 33 in Title 21-Food and Drugs, Chapter I- Food and Drug Administration Department of Health and Human Services (2003) 21CFR333.310,
17. M Liebert, Final Report on the Safety Assessment of 2-Methylresorcinol and Resorcinol, J Amer College of Toxicology 5(3) 167-203 (1986)
18. Resorcinol, Skin Deep Database, Environmental Working Group (2013)
19. Coal Tar Dye Issues, David Suzuki Foundation (2013)
20. Chemicals Known Or Suspected To Cause Cancer Or Reproductive Toxicity, Safe Cosmetics Program, California Department of Public Health Occupational Health Branch California (2013)

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