Synthetic dyes can make a cleaner blue, a hand wash pink, or a personal-care product green.

What they generally do not do is make that product clean better, remove odor more effectively, improve skin performance, or increase antimicrobial activity.

Their principal purpose is visual.

Color can influence how consumers interpret a product—what they expect it to smell like, how strong they believe it is, and even how effectively they expect it to clean. Research specifically examining formulated detergent found that appearance plays an important role in consumers' perception of cleaning effectiveness.¹

Color can serve another purpose as well: making a product look more uniform than the underlying formulation naturally is.

Raw-material source and purity, feedstock differences, processing conditions, particle size, trace impurities, storage, and normal aging can all influence the appearance of a finished formulation. In the detergent study, changing the source and purity of raw materials measurably changed the color of the finished product, as did manufacturing conditions and particle size.¹

Those visual differences do not necessarily mean that the product's functional performance has changed.

A dye can therefore do more than create an attractive color. It can mask normal batch-to-batch or age-related color variation, producing a visually standardized product even when the underlying formulation might naturally look slightly different.

That may be commercially useful.

It is not necessarily chemically necessary.

The U.S. Food and Drug Administration explicitly recognizes this broader function of color additives in another consumer-product category: FDA identifies offsetting color loss caused by storage conditions and correcting natural variations in color among the reasons color additives are used in foods.² Food and household cleaners are regulated differently, but the example illustrates an established technical use of colorants—making products appear more visually consistent.

At No Nines™, that distinction matters.

If a product performs within its appropriate specifications, a slight natural difference in color does not make one bottle more effective than another. We would rather measure and control the characteristics that actually determine product performance than add another ingredient simply to make every batch look artificially identical.

And if an ingredient is being added primarily to change—or conceal—the way a formulation looks rather than to improve what it does, we ask a simple question:

Why add the exposure at all?

That is particularly relevant because “synthetic dye” does not describe one chemical. It encompasses many different chemical structures with different toxicological and environmental profiles. Some have relatively low-hazard profiles. Others—or particular chemicals associated with their manufacture or metabolism—have raised significant concerns involving carcinogenicity, sensitization, persistence, or environmental toxicity.³⁴⁵⁶

So our position is not that every synthetic dye is equally hazardous.

It is that color alone is not a compelling reason to add another chemical exposure to a product that works without it.

That is why synthetic dyes are excluded under the No Nines™ Standard™.

No Nines™ Standard™

Effective chemistry doesn't require unnecessary exposure.

Our ingredient decisions consider not only whether an ingredient can perform a function, but also how much is required, how people are exposed to it, what happens when it is misused, and whether a different chemistry can accomplish the intended purpose with a more favorable exposure profile.

For synthetic dyes, the question is even more fundamental:

Does the product need the ingredient at all?

For No Nines™, the answer is no.

We do not need to color a cleaner blue to make it clean.

We do not need to make a skin product pink or green to make it perform.

We do not need to add color to a baby, pet, personal-care, or household product simply because consumers have been conditioned to associate a particular color with a particular function.

And we do not need to use synthetic color simply to conceal harmless differences in the natural appearance of a formulation.

We would rather let the chemistry do the work.

What are synthetic dyes?

Synthetic dyes are manufactured organic colorants designed to absorb particular wavelengths of visible light and impart color to a product.

The term encompasses numerous chemical families, including azo, triphenylmethane, xanthene, indigoid, anthraquinone, and other dye structures.

Their toxicological characteristics vary substantially according to molecular structure, purity, concentration, metabolites, route of exposure, and degradation products.

Many modern synthetic organic colorants are manufactured from petroleum-derived raw materials.

The familiar term “coal-tar dye” is largely historical. FDA explains that many synthetic colors subject to its certification system are now derived primarily from petroleum, although the “coal-tar” terminology originated when those chemical classes were produced from coal tar or chemically equivalent intermediates.⁷

Calling every modern synthetic colorant literally “coal-tar derived” would therefore not be chemically accurate.

A more precise description is:

Many synthetic dyes belong to chemical classes historically developed from coal-tar chemistry and today are manufactured primarily from petroleum-derived intermediates.

Petroleum origin by itself does not establish toxicity. The relevant questions are the identity of the particular dye, its impurities, metabolites, concentration, route and amount of exposure, and environmental fate.

Color has a purpose — but it is usually not a cleaning purpose

Colorants technically perform a function in a formulation:

They provide color.

But that should not be confused with cleaning or therapeutic performance.

A dye ordinarily does not:

• lift grease or soil;
• dissolve mineral deposits;
• reduce surface tension;
• neutralize odors;
• moisturize skin;
• support the skin barrier;
• provide the primary antimicrobial action of a formulation; or
• improve the underlying cleaning chemistry.

Instead, color frequently contributes to product identification, appearance, branding, consumer expectation, and perceived performance.

Research published in Particuology examined the color of a formulated detergent and stated that the appearance of detergent powder plays an important role in consumers' perception of its effectiveness for cleaning applications.¹

The study also demonstrated something particularly relevant to formulation.

Changes in raw-material grade and source, impurity levels, particle size, drying temperature, manufacturing conditions, and optical-brightener application changed the appearance of the finished detergent.¹

In other words, appearance can vary because of the materials and manufacturing process—not because the product suddenly stopped cleaning.

A liquid that is deep blue may look “powerful.”

Green may suggest botanical or environmentally friendly.

Pink may imply gentle or feminine.

Clear may suggest purity or simplicity.

And two otherwise acceptable batches may be perceived as different merely because one is slightly darker, yellower, or less clear than the other.

Those perceptions can be commercially powerful.

They are not measurements of performance.

For No Nines™, perceived performance is not a reason to formulate an unnecessary ingredient into a product.

Color can mask normal variation

Manufactured formulations are not always visually identical without intervention.

Raw materials themselves can vary slightly between suppliers, production lots, geographic sources, and feedstocks. Small differences in purity or trace constituents can affect color. Manufacturing temperature, mixing conditions, exposure to light or air, storage conditions, and normal product aging may also affect appearance.

The detergent research by Manga and colleagues demonstrated this directly. Reducing impurities by changing the raw-material source improved color definition, while particle size, drying conditions, and processing choices also affected the finished product's appearance.¹

Synthetic color can make those underlying differences much less visible.

This can create a consistent visual identity from bottle to bottle even when the uncolored formulation might show slight natural variation.

Colorants are used for comparable reasons in other industries. FDA identifies several purposes for food color additives, including:

• offsetting color loss associated with light, air, temperature, moisture, and storage;
• correcting natural color variation;
• enhancing naturally occurring color; and
• adding color to products that otherwise have little or none.²

FDA's food-color regulations do not govern household cleaners, and the safety assessment for a food color cannot simply be transferred to a cleaning formulation. The relevance here is the recognized function of added color: colorants can be used not merely to make something attractive, but also to minimize visible variation.

That can matter because consumers commonly interpret changes in appearance as changes in quality.

But appearance and performance are not the same measurement.

A slight change in the natural hue of a formulation may occur while the characteristics responsible for its performance remain within specification.

Conversely, a color change can sometimes signal genuine degradation or instability.

That is precisely why color alone is not an adequate measure of product stability.

The appropriate approach is to establish the critical attributes that determine whether a formulation remains stable and functional and then measure those attributes directly.

Adding dye may make a product continue to look the same.

It does not prove that the chemistry is the same.

For No Nines™, we would rather evaluate the chemistry than disguise its appearance.

If normal variation in color does not affect safety, stability, or performance, we do not believe it needs to be hidden simply to make every batch look artificially identical.

Why regulators evaluate colorants even when only small amounts are used

Colorants are generally used at relatively low concentrations.

That does not mean they are automatically ignored in chemical-safety assessment.

EPA's Safer Choice program evaluates ingredients according to both their function and their human-health and environmental characteristics. EPA maintains specific criteria for colorants, polymers, preservatives, and related chemicals.³

EPA notes that chemicals within these categories can be complex molecules or mixtures and may have limited measured toxicity data. Some also have functionality associated with resistance to degradation, making persistence and inherent hazard characteristics relevant to evaluation.³⁸

EPA's framework considers human-health and environmental endpoints rather than assuming that an ingredient is inconsequential merely because it constitutes a small portion of a formulation.³

That does not mean EPA considers all colorants hazardous.

It means that:

“It's only there for color” is not the same thing as “it requires no toxicological consideration.”

That principle aligns closely with the No Nines™ Standard™.

Synthetic dyes are not one toxicological category

It would be scientifically inaccurate to say that synthetic dyes as a whole cause cancer or that every synthetic dye presents the same health risk.

They do not.

Chemical structure matters enormously.

One important historical example involves benzidine-based dyes.

The National Toxicology Program's 15th Report on Carcinogens lists dyes metabolized to benzidine as known human carcinogens.⁴

NTP explains that certain benzidine-based dyes can undergo reduction that releases free benzidine. Benzidine itself is also classified by NTP as a known human carcinogen.⁴

That finding applies to this particular class of dyes.

It should not be generalized to every synthetic colorant.

The International Agency for Research on Cancer has likewise evaluated particular aromatic amines and organic dyes individually rather than classifying all synthetic dyes as a single carcinogenic category.⁵

That distinction is central to the No Nines approach.

We are not arguing:

Synthetic dye = carcinogen.

The research does not support that blanket statement.

We are saying something more precise:

Synthetic dyes comprise many different chemicals. Some dye structures, metabolites, and dye-related intermediates have established serious toxicological concerns, while other colorants have substantially different hazard profiles. When color provides no necessary cleaning or therapeutic benefit, No Nines chooses not to introduce that additional chemistry in the first place.

Azo dyes illustrate why chemical structure matters

Azo dyes constitute one of the major classes of synthetic dyes and contain the characteristic –N=N– azo linkage.

Their safety cannot be determined simply from the word “azo.”

Depending on molecular structure, certain azo dyes can undergo reductive cleavage that produces aromatic amines.

Some resulting aromatic amines have demonstrated significant carcinogenic or mutagenic properties, while others have different toxicological profiles.

Solubility, bioavailability, chemical structure, and metabolism all influence the outcome.⁶

Golka, Kopps, and Myslak reviewed the carcinogenicity of azo colorants and described the established history of certain benzidine-derived dyes, including the metabolic conversion of specific dyes to carcinogenic amine precursors. They also discussed important differences between soluble dyes and less-bioavailable pigments.⁶

That research illustrates why broad claims about all synthetic dyes should be avoided.

It also illustrates the formulation question No Nines asks:

If the ingredient contributes primarily color, what is gained by introducing another chemical whose identity, metabolites, impurities, environmental fate, and exposure must then be considered?

For us, not enough.

Purity and impurities matter too

The colorant molecule itself is not always the entire safety question.

Manufactured chemicals can contain residual starting materials, intermediates, reaction byproducts, or other impurities.

FDA's regulatory system for certain synthetic color additives used in foods, drugs, and cosmetics demonstrates the importance regulators place on chemical identity and purity.

Many synthetic colors subject to FDA certification must meet defined composition and purity requirements, and batches are analyzed before certification for permitted uses.⁷

Household cleaning products operate under different regulatory frameworks, so FDA color-certification requirements should not be interpreted as universally applying to household cleaners.

But the underlying chemical principle remains relevant:

Colorants are chemical ingredients, not simply visual decoration. Their identity and purity matter.

What happens after the product goes down the drain?

Cleaning products ultimately enter wastewater streams.

That makes environmental fate relevant even for ingredients that may be included at relatively low concentrations.

Again, synthetic dyes cannot be treated as one environmental category.

Different structures can have very different characteristics involving biodegradation, persistence, aquatic toxicity, and transformation products.

EPA's Safer Choice criteria specifically evaluate colorants as a functional class and consider both human-health and environmental characteristics.³⁸

EPA notes that resistance to degradation can be part of the desired functionality of some colorants and related chemicals, which is one reason their inherent hazard and environmental-fate characteristics warrant evaluation.³

The contribution from colorants in household products should be kept in perspective. Industries such as textile manufacturing use vastly larger quantities of dyes and represent much more significant sources of dye-containing wastewater.

But formulation decisions still occur ingredient by ingredient.

If a colorant is unnecessary to make a cleaner perform, No Nines sees little reason to add another chemical that must first be manufactured, transported and incorporated into the product—and ultimately enter the waste stream.

The simpler formulation question

There are circumstances in which color has a legitimate functional purpose.

Color may be important for:

• product identification;
• safety coding;
• process control;
• diagnostic applications;
• distinguishing chemicals that should not be confused; or
• products in which coloration itself is the intended function.

An ordinary household cleaner, skin mist, baby product, pet product, or personal-care formulation is different.

When color is added primarily because someone expects bathroom cleaner to be blue, soap to be pink, or a “natural” product to be green, we do not believe that visual convention justifies another ingredient.

And when synthetic color is added to make every production lot appear identical—or to conceal normal visual changes that do not affect performance—we would rather explain the chemistry than disguise it.

The No Nines™ Standard™ is not built around the idea that every excluded ingredient is equally dangerous.

It is built around a different formulation philosophy:

Every ingredient should earn its place.

Synthetic dyes do not improve the cleaning chemistry.

They do not improve our HOCl chemistry.

They do not improve the performance of our skin, baby, pet, or personal-care products.

They can change what a product looks like.

They can influence what consumers expect it to do.

And they can make natural differences among raw materials, production batches, or product age less visible.

None of those functions makes the underlying chemistry perform better.

For us, that isn't enough.

So we leave them out.

Published Sources & Further Reading

1. Manga MS, Willis D, Ali NM, York DW. “The impact of raw material properties and process conditions on the color of a powdered formulated detergent product.” Particuology. 2019;45:35–41. DOI: 10.1016/j.partic.2019.01.002.
The study evaluated factors affecting the color of formulated detergent powder and reported effects from raw-material grade and impurities, particle size, drying conditions, processing methods, and optical-brightener application. The authors also identified product appearance as an important factor in consumer perception of cleaning effectiveness.

2. U.S. Food and Drug Administration. Color Additives in Foods. FDA, current consumer and regulatory guidance, 2024–2026.
FDA identifies several purposes for color additives, including offsetting color loss caused by light, air, temperature, moisture and storage conditions; correcting natural variations in color; enhancing naturally occurring color; and adding color to otherwise colorless products. This source concerns foods rather than household cleaners and is cited to document recognized functional reasons for adding colorants.

3. U.S. Environmental Protection Agency. Safer Choice Criteria for Colorants, Polymers, Preservatives, and Related Chemicals. EPA Safer Choice Program. Criteria originally developed under the Design for the Environment/Safer Choice program and maintained as part of the current Safer Choice ingredient-review framework.
EPA evaluates colorants according to human-health and environmental criteria and recognizes that colorants may be chemically complex, may lack complete measured toxicological datasets, and may have functionality associated with resistance to degradation.

4. National Toxicology Program, U.S. Department of Health and Human Services. 15th Report on Carcinogens: Benzidine and Dyes Metabolized to Benzidine. 2021. Research Triangle Park, NC: National Toxicology Program.
Benzidine and dyes metabolized to benzidine are listed as known to be human carcinogens. Benzidine was first listed in the First Annual Report on Carcinogens in 1980; dyes metabolized to benzidine were first listed as a class in the Ninth Report on Carcinogens in 2000.

5. International Agency for Research on Cancer. Some Aromatic Amines, Organic Dyes, and Related Exposures. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 99. 2010. Lyon, France: International Agency for Research on Cancer, World Health Organization. ISBN 978-92-832-1299-7.
IARC evaluated individual aromatic amines, organic dyes, and related occupational exposures based on epidemiological, experimental-animal, and mechanistic evidence rather than treating all synthetic dyes as a single toxicological class.

6. Golka K, Kopps S, Myslak ZW. “Carcinogenicity of azo colorants: influence of solubility and bioavailability.” Toxicology Letters. 2004;151(1):203–210. DOI: 10.1016/j.toxlet.2003.11.016. PMID: 15177655.
The review discusses the metabolism and carcinogenicity of particular benzidine-derived azo dyes and explains the importance of chemical structure, solubility, bioavailability, and formation of aromatic-amine precursors.

7. U.S. Food and Drug Administration. Color Additives and Cosmetics: Fact Sheet. FDA. See also Federal Food, Drug, and Cosmetic Act §721, 21 U.S.C. §379e, and 21 CFR Parts 70–82.
FDA describes the regulation, certification, identity, and purity requirements applicable to color additives within its jurisdiction. FDA also explains the historical use of the term “coal-tar colors” and the modern use of petroleum-derived starting materials for many certifiable synthetic organic colorants.

8. U.S. Environmental Protection Agency. EPA's Safer Choice and Design for the Environment (DfE) Standard. Originally issued 2009; revised 2011, 2012, 2015, and August 2024. See the sections addressing colorants, polymers, preservatives, and related chemicals.
The Standard describes EPA's functional-class approach to ingredient review and its consideration of human-health hazards, environmental toxicity, environmental fate, persistence, and available measured or modeled toxicological data.