Formaldehyde-releasing preservatives are designed to do exactly what their name suggests: release small amounts of formaldehyde into a formulation over time to control microbial growth.

Common examples include DMDM Hydantoin, Quaternium-15, Diazolidinyl Urea, Imidazolidinyl Urea, Bronopol, and Sodium Hydroxymethylglycinate. The U.S. Food and Drug Administration identifies these ingredients specifically as formaldehyde-releasing preservatives and potential cosmetic allergens.¹

The concern is not simply that formaldehyde appears somewhere in the chemistry. It is that these preservatives can create ongoing formaldehyde exposure during the useful life of a product, and the amount released can change with formulation chemistry, pH, temperature, storage time, and other conditions.²

That matters because formaldehyde is one of the most extensively evaluated chemical hazards in this ingredient category.

The International Agency for Research on Cancer classifies formaldehyde as carcinogenic to humans (Group 1).³ The U.S. National Toxicology Program lists it as known to be a human carcinogen.⁴ In 2024, the U.S. Environmental Protection Agency concluded in its comprehensive IRIS assessment that formaldehyde is carcinogenic to humans by the inhalation route and can also produce respiratory and allergic effects.⁵

Formaldehyde is also a well-established skin sensitizer, meaning repeated exposure can cause the immune system to become sensitized and subsequently produce allergic contact dermatitis.⁶

For No Nines™, that creates an unnecessary exposure pathway.

We do not formulate with formaldehyde, and we do not use preservatives designed to generate formaldehyde after the product is made.

That standard applies across our formulations — whether a product is intended for skin, personal care, babies, pets, or the home.

What are formaldehyde releasers?

Water-containing products generally require some method of controlling bacteria, yeast, and mold during storage and use.

One traditional solution has been a class of preservatives commonly called formaldehyde donors or formaldehyde releasers.

Rather than adding free formaldehyde directly to a formulation, manufacturers can use compounds that decompose or undergo chemical equilibrium reactions that produce formaldehyde.

Common examples identified by FDA include:¹

• DMDM Hydantoin
• Quaternium-15
• Diazolidinyl Urea
• Imidazolidinyl Urea
• Bronopol (2-bromo-2-nitropropane-1,3-diol)
• Sodium Hydroxymethylglycinate
• 5-bromo-5-nitro-1,3-dioxane

These chemicals are not all toxicologically identical, and they do not release identical amounts of formaldehyde under identical conditions.

What they share is their ability to generate formaldehyde in the finished product.

The formaldehyde is not necessarily static

One reason this preservative system is different from simply measuring the concentration of an ingredient when a product is manufactured is that formaldehyde release can change over time.

A laboratory study examining eight formaldehyde-releasing preservatives found that formaldehyde release depended on the specific preservative, formulation matrix, pH, storage time, and temperature. Higher temperatures and longer storage were associated with greater formaldehyde release under the conditions studied.²

In other words, the concentration of free formaldehyde in a product is not necessarily determined solely by how much free formaldehyde was present on the day the product was manufactured.

The preservative itself can act as a continuing source.

That is the point of the chemistry: a reservoir of preservative activity is maintained as the formulation ages.

This also means that simply reading a product's ingredient panel does not tell a consumer exactly how much free formaldehyde is present at a particular point in the product's shelf life.

Research evaluating formaldehyde-releasing preservatives in cosmetics has found that several commonly used releasers can, under appropriate formulation conditions, generate concentrations of free formaldehyde sufficient to trigger dermatitis in people already sensitized to formaldehyde.⁷

Formaldehyde is a recognized human carcinogen

Formaldehyde has been evaluated by multiple major scientific and governmental bodies.

International Agency for Research on Cancer

IARC evaluated formaldehyde in its Monographs on the Evaluation of Carcinogenic Risks to Humans and classifies it as: Group 1 — carcinogenic to humans.³

The classification is based primarily on evidence from occupational and inhalation exposures, including studies involving workers with substantially greater formaldehyde exposure than would normally occur from use of a cosmetic product.

National Toxicology Program

The U.S. National Toxicology Program lists formaldehyde as known to be a human carcinogen in the 15th Report on Carcinogens.⁴

NTP's evaluation cites human epidemiological evidence involving cancers including nasopharyngeal and sinonasal cancers and myeloid leukemia.

U.S. Environmental Protection Agency

In 2024, EPA completed its extensive IRIS Toxicological Review of Formaldehyde (Inhalation).

EPA concluded that formaldehyde is carcinogenic to humans by the inhalation route of exposure and identified evidence involving nasopharyngeal cancer, sinonasal cancer, and myeloid leukemia.⁵

This distinction is important scientifically: classification of formaldehyde as a human carcinogen does not mean that a cosmetic containing a formaldehyde-releasing preservative has itself been demonstrated to cause cancer in consumers.

The cancer classifications establish the hazard of formaldehyde itself, particularly from inhalation exposures studied in occupational populations.

For formaldehyde-releasing preservatives, the more directly demonstrated consumer concern is their ability to produce formaldehyde exposure and to cause or provoke skin sensitization and allergic contact dermatitis.

Skin sensitization is a well-documented concern

Formaldehyde is one of the classic causes of allergic contact dermatitis, and formaldehyde-releasing preservatives have been studied extensively in dermatology.

A 2022 clinical review in Contact Dermatitis identified five major formaldehyde-releasing preservatives of continuing clinical importance:

• Quaternium-15
• Diazolidinyl Urea
• DMDM Hydantoin
• Imidazolidinyl Urea
• Bronopol⁶

Exposure can produce localized dermatitis involving areas such as the face and hands, as well as more widespread reactions in susceptible individuals.⁶

Importantly, people may react either to formaldehyde released from the preservative, to the preservative molecule or its other degradation products, or through a combination of mechanisms.

A major review of formaldehyde releasers concluded that there is a clear relationship between formaldehyde allergy and reactions to several formaldehyde-releasing preservatives.⁷

Newer research confirms that sensitization remains relevant

This is not simply a historical concern associated with older cosmetic formulations.

A 2026 systematic review and meta-analysis analyzed 158 studies involving more than 1.3 million dermatitis patients.⁸

Among this clinical population, the pooled prevalence of contact allergy was:

• 2.88% for formaldehyde
• 2.76% for bronopol
• 1.89% for Quaternium-15
• 1.42% for Diazolidinyl Urea
• 1.37% for DMDM Hydantoin
• 1.20% for Imidazolidinyl Urea⁸

These figures apply to patients undergoing evaluation for dermatitis, not to the general population, but they demonstrate that formaldehyde and formaldehyde-releasing preservatives remain clinically relevant contact allergens.

Regulators have responded to formaldehyde exposure from these preservatives

European regulators have taken particularly specific action.

Free formaldehyde itself is prohibited for use as a cosmetic ingredient in the European Union because of its carcinogenic classification.¹⁰

Formaldehyde-releasing preservatives may still be permitted under specified conditions, but European regulators substantially tightened labeling requirements after reviewing sensitization data.

In 2021, the European Commission's Scientific Committee on Consumer Safety concluded that the previous labeling threshold of 0.05% — 500 ppm — did not adequately protect consumers already sensitized to formaldehyde.⁹

The committee recommended reducing the threshold by a factor of 50.

Commission Regulation (EU) 2022/1181 subsequently requires cosmetics containing formaldehyde-releasing substances to carry the warning:

“releases formaldehyde”

when the total concentration of released formaldehyde exceeds 0.001%, or 10 ppm.¹⁰

That requirement applies to the total formaldehyde released, regardless of whether one or multiple formaldehyde-releasing ingredients are responsible.

Quaternium-15 has received even stronger regulatory treatment.

In 2019, the European Union removed Quaternium-15 from its list of permitted cosmetic preservatives and added it to the list of substances prohibited in cosmetics after regulators determined that available evidence was insufficient to establish its safety for cosmetic use.¹¹

Why use a preservative that creates another chemical exposure?

Preservation is important.

Products containing water must be formulated so that harmful microorganisms do not proliferate during manufacturing, storage, and normal consumer use.

The question is not whether preservation is necessary.

The question is which preservation chemistry is appropriate.

Formaldehyde-releasing preservatives represent one way to control microorganisms, but they accomplish that function partly through the controlled generation of formaldehyde — a recognized human carcinogen, respiratory toxicant at sufficient inhaled exposures, and established contact allergen.³⁻⁶

Other preservative strategies exist.

For No Nines™, that makes formaldehyde release an unnecessary part of the exposure profile.

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.

Formaldehyde-releasing preservatives can perform a legitimate preservation function.

But their function depends on chemistry capable of generating formaldehyde in the finished product, and formaldehyde is both a recognized human carcinogen and an established skin sensitizer. The amount released can also vary with formulation conditions, storage time, temperature, and pH.²

For that reason, No Nines™ formulations do not contain formaldehyde or formaldehyde-releasing preservatives such as DMDM Hydantoin, Quaternium-15, Diazolidinyl Urea, or Imidazolidinyl Urea.

Not because preservation is unnecessary.

Because formaldehyde release is unnecessary.

Published Sources & Further Reading

1. U.S. Food and Drug Administration. Allergens in Cosmetics. FDA, Center for Food Safety and Applied Nutrition. Identifies formaldehyde and formaldehyde-releasing cosmetic ingredients including Bronopol, Diazolidinyl Urea, DMDM Hydantoin, Imidazolidinyl Urea, Sodium Hydroxymethylglycinate and Quaternium-15. Current FDA consumer guidance; accessed October 2026.

2. Lv C, Hou J, Xie W, Cheng H. Investigation on formaldehyde release from preservatives in cosmetics. International Journal of Cosmetic Science. 2015;37(5):474-478. DOI: 10.1111/ics.12212. PMID: 25704726.

3. International Agency for Research on Cancer. Formaldehyde. In: Chemical Agents and Related Occupations. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 100F. Lyon, France: International Agency for Research on Cancer; 2012:401-435. ISBN 978-92-832-1323-9. Formaldehyde classified as carcinogenic to humans, Group 1.

4. National Toxicology Program. Formaldehyde. Report on Carcinogens, Fifteenth Edition. Research Triangle Park, NC: U.S. Department of Health and Human Services, National Toxicology Program; 2021. CAS No. 50-00-0. Classification: Known to Be a Human Carcinogen.

5. U.S. Environmental Protection Agency. IRIS Toxicological Review of Formaldehyde (Inhalation). Washington, DC: Center for Public Health and Environmental Assessment, Office of Research and Development; 2024. EPA/635/R-24/162. CASRN 50-00-0. EPA conclusion: carcinogenic to humans by the inhalation route.

6. Goossens A, Aerts O. Contact allergy to and allergic contact dermatitis from formaldehyde and formaldehyde releasers: A clinical review and update. Contact Dermatitis. 2022;87(1):20-27. DOI: 10.1111/cod.14089. PMID: 35229319.

7. de Groot AC, White IR, Flyvholm MA, Lensen G, Coenraads PJ. Formaldehyde-releasers in cosmetics: relationship to formaldehyde contact allergy. Part 2: Patch test relationship to formaldehyde contact allergy, experimental provocation tests, amount of formaldehyde released, and assessment of risk to consumers allergic to formaldehyde. Contact Dermatitis. 2010;62(1):18-31. DOI: 10.1111/j.1600-0536.2009.01631.x. PMID: 20136876.

8. Karimian K, Isufi D, Jensen MB, Søgaard R, Johansen JD, Schwensen JFB. The Prevalence of Contact Allergy to Formaldehyde and Formaldehyde Releasers: A Systematic Review and Meta-Analysis. Contact Dermatitis. 2026;95(2):125-147. DOI: 10.1111/cod.70172. PMID: 42035787. PMCID: PMC13327177.

9. Scientific Committee on Consumer Safety (SCCS). Scientific Advice on the Threshold for the Warning “Contains Formaldehyde” in Annex V, Preamble Point 2 for Formaldehyde-Releasing Substances. European Commission; final version May 7, 2021. SCCS/1632/21.

10. European Commission. Commission Regulation (EU) 2022/1181 of 8 July 2022 amending the preamble of Annex V to Regulation (EC) No. 1223/2009 on cosmetic products. Official Journal of the European Union. 2022;L184:3-4. Establishes the “releases formaldehyde” labeling threshold at 0.001% (10 ppm) total released formaldehyde.

11. European Commission. Commission Regulation (EU) 2019/831 of 22 May 2019 amending Annexes II, III and V to Regulation (EC) No. 1223/2009 on cosmetic products. Official Journal of the European Union. 2019. Removes Quaternium-15 from the permitted-preservative list and adds it to the list of substances prohibited in cosmetic products.