Acid Red 92: properties, uses, pros, cons, safety, alternatives

Acid Red 92 (CI 45410) is a chemical compound, a synthetic dye known as  D&C Red No. 28, Solvent Red 48.

The name describes the structure of the molecule:

• CI stands for "Colour Index", which is an international system used to classify dyes and pigments. This nomenclature is universally employed to standardize the naming of dyes across different industries.
• 45410 is a specific identifier within the Colour Index that denotes a particular red dye. This number is assigned to a specific dye to facilitate its identification and ensure consistency in manufacturing and usage.

Acid Red 92 is a synthetic dye used primarily in cosmetics, hair colorants, and some personal care products. The chemical compound belongs to the xanthene dye family and is characterized by its bright red-pink hue. It exists in various forms, including 3,4,5,6-Tetrachloro-2-(1,4,5,8-tetrabromo-6-hydroxy-3-oxoxanthen-9-yl)benzoic acid and its insoluble barium, strontium, and zirconium lakes, salts, and pigments. Another related compound is Fluorescein, 2',4',5',7'-tetrabromo-4,5,6,7-tetrachloro-, disodium salt, which shares the same CI 45410 designation.

Chemical Composition and Structure

Acid Red 92 includes halogenated derivatives of fluorescein, such as tetrachlorofluorescein and tetrabromofluorescein. The various forms include both soluble salts (like sodium salts) and insoluble pigments (like lakes), which are used depending on the formulation needs. The structure is based on the xanthene ring, a fluorescent and highly chromatic structure, contributing to the vivid color and fluorescence observed in many formulations.

Physical Properties

Acid Red 92 typically appears as a red to pink powder, depending on its specific form (salt or lake). The dye is soluble in oils and organic solvents but can also form insoluble lakes, which are used in certain makeup products for longer-lasting pigmentation. It provides a bright, vivid red-pink color, often used in lipsticks, blushes, and hair dyes.

Production Process

It is synthesized through a chemical process that involves halogenation (with bromine and chlorine) of fluorescein derivatives. These halogenated xanthene derivatives are further processed to produce either soluble salts or insoluble lake pigments, depending on the intended use in formulations.

Chemical Industrial Synthesis Process

• Selection of base materials. The process begins with the selection of sulfonated organic compounds, which are essential for the synthesis of the dye.
• Fusion with a base. The selected compounds are then fused with a base, typically sodium hydroxide, to form the corresponding salt.
• Precipitation. The salt is precipitated in an aqueous solution to form the pigment.
• Filtration. After precipitation, the pigment is filtered to remove impurities and unreacted residues.
• Drying. The filtered pigment is dried to reduce moisture content.
• Laking. To enhance the stability of the pigment, it is treated with substrates such as aluminum lake, which helps to bind the color and prevent smudging.
• Quality control. Each batch of Red 28 Lake produced undergoes rigorous quality testing to ensure that specifications are met.

Chemical name 2',4',5',7'-tetrabromo-4,5,6,7-tetrachloro-3',6'-dihydroxyspiro[2-benzofuran-3,9'-xanthene]-1-one

It contains a xanthene core that makes the colour fluorescent.

Applications

• Cosmetics: Acid Red 92 is  used in colored cosmetics, such as lipsticks, blushes, and eyeshadows. It provides a bright, intense color that is stable and long-lasting.

• Hair Colorants: Acid Red 92 is an ingredient in hair dyes due to its vivid color and ability to provide vibrant shades. It is especially used in temporary or semi-permanent hair colors.

• Other Personal Care Products: The dye can also be found in various personal care items like soaps and bath products for its coloring properties.

Cosmetics safety

It is a restricted ingredient as IV/79  a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported: 

• 3,4,5,6-Tetrachloro-2-(1,4,5,8-tetrabromo-6-hydroxy-3-oxoxanthen-9-yl)benzoic acid and its insoluble barium, strontium and zirconium lakes, salts and pigments
• Fluorescein, 2',4',5',7'-tetrabromo-4,5,6,7- tetrachloro-, disodium salt (CI 45410)

Colorant. This ingredient has the primary function of colouring the solution in which it is inserted in a temporary, semi-permanent or permanent manner, either alone or in the presence of the complementary components added for colouring.

Safety

SCCNFP experts noted:

"Acid Red 92 has been tested in two in vitro assays for the induction of gene mutations and 

chromosome aberrations in bacterial cells and in mammalian cells. An in vivo study for the 

induction of numerical/structural chromosome aberrations has been performed on mice. 

Under the conditions of the studies, the test item has been demonstrated to be devoid of the 

ability to induce gene mutations in bacterial and mammalian cells, to induce chromosome 

aberrations in mammalian cells in vitro, and numerical/structural chromosome aberrations in 

vivo in mice bone marrow. 

Carcinogenicity 

A long-term carcinogenicity study with mice showed an increased frequency of pituitary 

tumours among the dosed females. The frequency of the other tumours was not affected by the 

presence of Acid Red 92 in the diet. The study is not adequately reported."

Regulations and Warnings

Under the European Cosmetics Regulation (EC) No 1223/2009, CI 45410 is subject to specific provisions, listed as IV/79 and III/270 under its name Acid Red 92. These regulations are in place to ensure the safe use of this synthetic colorant in cosmetics and personal care products.

Wording of Conditions of Use and Warnings

For products containing Acid Red 92, especially hair colorants, the following labeling and warnings must be printed on the product packaging:

• Mixing Ratio: The exact ratio of ingredients used in the hair dye formulation must be indicated.
• Allergy Warning:
  • “Hair colorants can cause severe allergic reactions. Read and follow instructions.”
  • “This product is not intended for use on persons under the age of 16.”
  • “Temporary ‘black henna’ tattoos may increase your risk of allergy.”
• Usage Restrictions: The label must advise users not to color their hair if:
  • They have a rash on their face or a sensitive, irritated, or damaged scalp.
  • They have experienced any reaction after coloring their hair in the past.
  • They have reacted to a temporary ‘black henna’ tattoo in the past.

Health and Safety Considerations

Safety in Use

While Acid Red 92 is considered safe for use in cosmetics, it must be used in accordance with the regulations to minimize any potential risks. The warnings regarding its use in hair colorants highlight the importance of conducting patch tests before application, particularly for individuals with sensitive skin or a history of allergic reactions to dyes or henna.

Allergic Reactions

Allergic reactions to Acid Red 92, particularly when used in hair dyes, can occur. Users should follow the warning labels carefully, especially if they have a history of allergies to hair dyes or temporary black henna tattoos, as these increase the risk of an allergic reaction.

Toxicity and Carcinogenicity

Caution is advised for individuals with sensitive skin or a history of allergies.

Environmental and Safety Considerations

Acid Red 92 is a synthetic dye, and as with many synthetic colorants, its environmental impact should be considered, especially in terms of waste and pollution during manufacturing. Regulatory guidelines ensure that its use in products is safe for consumers.

Regulatory Status

The use of Acid Red 92 is strictly regulated in the European Union under the Cosmetics Regulation, which requires specific labeling and concentration limits to ensure safety. The FDA in the United States also regulates the use of this dye in cosmetics, ensuring it meets safety standards for consumer use.

Applications Under Strict Control

• Hair Dyes: Used with specific mixing ratios and warnings about allergic reactions and age restrictions.

• Cosmetic Products: Widely used in lipsticks, eyeshadows, and blushes, with labeling required to indicate its presence and usage instructions.

• Temporary Tattoos: May be used in formulations for cosmetic tattoos, with strong warnings regarding allergies from black henna.

Alternatives

Molecular Formula C₂₀H₄Br₄Cl₄O₅

Molecular Weight  829.6 g/mol

CAS  18472-87-2

UNII    767IP0Y5NH

EC Number   242-355-6

UNII 2LRS185U6K

DTXSID2031089

Synonyms: 

CI 45410

Eosin Blue

D&C Red No. 27

D&C Red No. 28

Solvent Red 48

Red 28 Lake

Acid Red 92

References_____________________________________________________________________

(1) https://ec.europa.eu/health/ph_risk/committees/sccp/documents/out262_en.pdf