Formaldehyde (Methylene Glycol)

What Is It?

Formaldehyde in its pure form is a colorless gas. However, formaldehyde is rarely used as a gas but, instead, is dissolved in water to make a solution known as formalin. Formalin exists as an equilibrium mixture of formaldehyde and its hydrated form, methylene glycol. Other ingredients that slowly release small amounts of formaldehyde (called formaldehyde-releasers) may also be added to cosmetics and personal care products as preservatives.

Why Is It Used?

Formalin may be used in nail hardeners, where it bonds with the keratin that occurs naturally in the nails, making the nails harder. Formaldehyde and formaldehyde-releasing ingredients (e.g., DMDM hydantoin, imidazolidinyl urea and diazolidinyl urea) are also used as preservatives to kill microorganisms, or to prevent or inhibit their growth in products. Preservatives are ingredients designed to help ensure the safety of products by protecting them against contamination by microorganisms during storage and use by consumers.

Learn more about the use of formaldehyde in nail hardener products and how preservatives protect cosmetics and personal care products.

Scientific Facts

Formaldehyde containing polymers, such as tosylamide/formaldehyde resin, may also be used in cosmetics and personal care products. The formaldehyde in these compounds is tightly bound in the polymer molecule.

Safety Information

United States


The safety of formaldehyde has been assessed on several occasions by the Cosmetic Ingredient Review CIR Expert Panel. In 1984, the CIR Expert Panel evaluated the scientific data and concluded that formaldehyde in cosmetics products is safe for the vast majority of consumers. Because of skin sensitivity of some individuals to formaldehyde, the formulation and manufacture of cosmetics products should limit use to the minimal effective concentration of this agent, not to exceed 0.2%, measured as free formaldehyde. Furthermore, it could not be concluded that formaldehyde is safe in cosmetics products intended to be aerosolized. In 2006, formaldehyde came up for re-review by the Expert Panel, which decided there was no need to reopen the safety assessment at that time.In 2013, the Expert Panel published an amended safety assessment of formaldehyde and methylene glycol, concluding that they may be used safely in cosmetics if established limits are not exceeded and that they are safe for use in nail hardeners in the present practices of use and concentration, which includes instructions to avoid skin contact.

The Expert Panel also considered the safety of formaldehyde/methylene glycol in hair straightening products and determined that it depends on a number of factors, including concentration, amount of product applied, temperature used during the application process and ventilation provided at the point of use. The Panel concluded that formaldehyde and methylene glycol are unsafe in hair straightening products under present practices of use and concentration.

The Expert Panel further noted that the rapid, reversible formaldehyde/methylene glycol equilibrium in hair straightening products is different from the slow, irreversible release of formaldehyde resulting from formaldehyde-releasers. The slow-releasing preservatives may continue to be used safely in cosmetics at the levels established in their respective CIR safety assessments.


The U.S. Food and Drug Administration (FDA) reviewed the safety of formaldehyde and approved its use as an indirect food additive in adhesives in a number of materials having contact with food (21CFR175.105) and as a secondary direct food additive as a preservative in defoaming agents (21CFR173.340).

FDA addresses hair-smoothing products that release formaldehyde when heated on its website. It notes that such products (e.g., Brazilian Blowout and others) often contain formaldehyde, also known as formalin or methylene glycol. When the hair-smoothing solutions are heated, the formaldehyde in the products is released into the air as a gas. Both the salon professionals and their clients are at risk of inhaling the released formaldehyde if the professional salon using such a product is not properly ventilated. As hair-smoothing products increased in popularity in the late 2000s, FDA began receiving inquiries from consumers and salon professionals about the safety of products containing formaldehyde or related ingredients. In response to these concerns, in 2010, the agency began communicating with the public to provide information about the potential health effects of these products and how to recognize products containing formaldehyde or its liquid forms, formalin and methylene glycol. FDA continues to communicate with consumers about the potential risks associated with use of these products and evaluates products for safety and labeling on a case-by-case basis.

European Union (EU)

Formaldehyde and methylene glycol are listed in the Annex II list of substances prohibited in cosmetics products (Entries 1577 and 1579) and may not be used in cosmetics products marketed in Europe.


Health Canada permits the use of formaldehyde in non-aerosol cosmetics at concentrations up to 0.01%, in oral products at up to 0.1%, in non-oral products at up to 0.2% and in nail hardener products at up to 5%. Nail hardeners containing formaldehyde must be sold with nail shields, directions for use and a caution regarding sensitization potential.

Health Canada issued several advisories in 2010 regarding the product known as Brazilian Blowout and several other professional hair-smoothing products, indicating they contained unacceptable levels of formaldehyde. In 2014, Health Canada issued several additional warnings about professional hair- smoothing solutions that contain levels of formaldehyde above their set limits. They advised consumers and professional hair salons to not use such products.

CIR Safety Review (1984)

The CIR Expert Panel noted that formaldehyde is a normal metabolite of all mammals. Formaldehyde’s high reactivity is what makes it useful as a preservative but is also responsible for its irritant activity. The Expert Panel indicated that the toxic effects of formaldehyde are all concentration and time dependent. They concluded that formaldehyde can be used at concentrations that are not irritating.

CIR (2006)

An extensive number of new studies, along with updated information regarding types and concentrations of use, were considered by the Expert Panel. New clinical studies confirmed that formaldehyde can be a skin irritant and sensitizer but only at levels higher than the 0.2% free formaldehyde upper limit established in the 1984 CIR assessment. The developmental toxicity, genotoxicity and carcinogenicity of high doses of formaldehyde were also confirmed in the new studies, which further demonstrated a threshold effect (i.e., high doses are required before any effect is seen). Again, the limit on the amount of free formaldehyde established by the Expert Panel in 1984 precludes any risk as the result of use of cosmetics products containing formaldehyde.

European Union (EU)

Formaldehyde was historically listed in Entry 13 of Annex III to Regulation (EC) No 1223/2009 (list of restricted substances) for use as a nail hardener at concentrations of up to 5% in ready-for-use preparations. It was also historically listed in Entry 5 of Annex V (list of preservatives allowed in cosmetics) for use in oral products at concentrations up to 0.1% and in other products at concentrations up to 0.2%.

In 2014, formaldehyde was classified as a CMR (carcinogen, mutagen or reproductive toxicant) substance of category 1B by Commission Regulation (EU) No 605/2014. The classification became applicable in January 2016. Article 15 of EU Cosmetics Regulation (EC) No 1223/2009 provides that substances classified as CMR substances of category 1A, 1B or 2 are prohibited from use in cosmetics products. A CMR substance may, however, be used in cosmetics products by way of exception where, subsequent to their classification as CMR substances, certain conditions are fulfilled, including that no suitable alternative substances are available; an application is made for a particular use of the product category with a known exposure; and the substance has been evaluated by the EU Scientific Committee on Consumer Safety (SCCS) and found safe for use in cosmetics products. In November 2014, the SCCS concluded that, in its opinion, nail hardeners with a maximum concentration of about 2.2% free formaldehyde can be used safely to harden or strengthen nails.

However, on May 22, 2019, the EU cosmetics regulations were amended to delete formaldehyde from the list of restricted substances in Annex III since it had not been established that there were no suitable alternative substances available for the purpose of hardening nails. In addition, since no application was made for other uses of formaldehyde, the substance was also deleted from the list of preservatives allowed in cosmetics products in Annex V. As previously mentioned, formaldehyde was added to Annex II (list of substances prohibited in cosmetics products) and, as such, may no longer be used in cosmetics products marketed in Europe.


Cosmetic Ingredient Review (CIR)
EU Cosmetic Ingredient Inventory (CosIng)