Structural formula of aniline yellow in the group azo dyes


What is it?

“Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl. They are a commercially important family of azo compounds, i.e. compounds containing the linkage C-N=N-C.[1] Azo dyes are widely used to treat textiles, leather articles, and some foods.” Wikipedia

What are the effects?

This substance belongs to the groups:

The azo dyes, also called aryl azo compounds, is a large group of chemical compounds with vivid colors that share a similar molecular structure. The group includes, for example, congo red, aniline yellow, and Ci direct black.

There are broadly two different types of azo dyes; azo direct dyes and azo reactive (acid) dyes. The azo direct dyes have been linked to increased cancer risk, mutagenic and negative reproductive effects, while the azo reactive (acid) dyes have been linked to increased allergy risk. The dyes are also difficult to biodegrade in the environment and can accumulate in the marine food chain, which has lead to indirect exposure for humans through food that we eat. The different dyes will be highlighted and tagged accordingly to by Curious Chloride’s scanner.


The Swedish Chemicals Agency (KEMI) explains that the concern regarding these dyes is that some of them break down to aromatic amines; arylamines. Some of the dyes are classified as carcinogenic and causing “allergy on skin contact, irritating the eyes, being toxic by inhalation and if swallowed or being very toxic by inhalation, skin contact and if swallowed. Some of the arylamines have also been judged to be toxic or very toxic to aquatic organisms and to be capable of causing long-term adverse effects in the aquatic environment”

KEMI also writes that the breakdown to arylamines can take place during storage (affected by light and temperature) or in contact with the body’s own enzyme system (when for example sleeping in bedclothes or using color cosmetics containing the dyes).

Another important aspect of the azo dyes is that “the arylamines emitted from the azo dye can be absorbed by the skin and accumulate in the body”, KEMI again.

Environment and Climate Change Canada (ECCC) also reports that azo direct dyes and azo reactive dyes may persist in water, sediment, and soil. They have further found that the reactive dyes had induced effects in aquatic organisms already at low concentrations.

The ECCC have also found that the dyes “may have sensitization potential for individuals directly exposed to the concentrated dyes”

Both KEMI and ECCC warns especially about children and infants’ risk of exposure to these chemical dyes. They azo dyes are only loosely bonded to the textile fibres which means that exposure becomes easier. Prolonged contact with the child’s palms, when for example playing with an azo dyed toy, can drive exposure. High exposure for small children is also likely if they suck or chew on chemically dyed textiles, as they tend to do with soft toys or blankets. Small children are also at risk of being exposed to the chemicals through dust that often to a large part contains textile fibres.

Four azo dyes examples

Congo red – a “Substances of Very High Concern.”Classified as carcinogenic, mutagenic or toxic for reproduction (CRM) by the European Chemicals Agency (ECHA), “may cause cancer and is suspected of damaging the unborn child.”

Aniline yellow – Classified as a “Substances of Very High Concern” by ECHA, “may cause cancer, is very toxic to aquatic life with long lasting effects, is toxic if swallowed and may cause an allergic skin reaction.”

C.I. Direct Black 38 – on ECHA’s Candidate List of “Substances of Very High Concern”, identified as a CMR that “may cause cancer and is suspected of damaging the unborn child.”

C.I. Acid Red 114 – classified as a possible carcinogen and on the Red List* of Campaign for Safe Cosmetics, a project of Breast Cancer Prevention Partners (previously the Breast Cancer Fund).

Pigment Red 4 – also known as red 36, Aka228 or CI 12085 is a monazo color restricted for use in Canada due to potential health concerns.

*  “The Red List includes chemicals found in personal care products that pose serious, chronic health concerns including cancer, hormone disruption, and reproductive and developmental harm. The list also flags chemicals that are banned or have use restrictions by the U.S. or other world governments, ingredients that adversely impact worker health, and ingredients that are widely used in products marketed to women of color.” – Campaign for Safe Cosmetics

How is it used?

There are reportedly around 2000 azo dyes on the market today, representing around 60 – 80 % of all organic colorants. They have been described as the most important class of synthetic dyes and pigments and are present in most things colorful around us.

Some of the dyes can be found in cosmetics* and personal care products such as hair dyes, face masks, make-up, body lotions, hair conditioners, nail polish, lipsticks, sanitary napkins, and bath products. It is also common to use the dyes to color textiles, leather, and paper.

The azo colorants are a popular choice for the manufacturer since they are cheap and easy to use, especially since they color most fabrics, including for example cotton silk, wool, viscose, and synthetic fibers including polyamide and other plastics.

The dyes give strong and clear colors and are very common to find in the fabrics of furniture, clothing, shoes, and toys, to name a few.

Since they color such a wide variety of materials, a large number of people can be exposed to these types of dyes. KEMI warns that “There is a risk of exposure when wearing garments or accessories that contain azo dyes, or when sleeping in such bedclothes.”

The chemicals can migrate from garment to skin, and be absorbed by the pores through for example sweating.

Other uses of azo dyes include natural health products, permanent tattoo inks,  inks (f.ex. for printers), insecticides (substances used to kill insects), varnishes, waxes, paints, and lacquers.

Children might be exposed through creative and school/kindergarten material as the dyes also are used in finger and face paints.

We use the European Commissions definition of Cosmetics:
“Cosmetics range from everyday hygiene products such as soap, shampoo, deodorant, and toothpaste to luxury beauty items including perfumes and makeup”.

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