Formaldehyde-Releasing Preservatives: What's Actually Restricted, and Where

The short answer

DMDM hydantoin and quaternium-15 are preservatives added to shampoo, conditioner, lotion, and some hair-smoothing treatments to keep mold and bacteria from growing in the bottle. They work by releasing a small, ongoing amount of formaldehyde — enough to control microbes, not enough to smell it. That release mechanism is also why regulators treat them differently from formaldehyde itself, which is simply prohibited as a direct cosmetic ingredient everywhere it's regulated.

The restriction on these two isn't uniform, and that's the actually useful part of this page. One of them is banned outright in the European Union. The other is still permitted almost everywhere, including the US, but as of this year has to carry a warning label in the EU once its formaldehyde release crosses a fairly low threshold.

Where the concern came from

Formaldehyde is a well-established skin sensitizer, and the International Agency for Research on Cancer classifies it as a human carcinogen — but that classification is tied to high, prolonged, mostly inhaled exposure, not to trace amounts absorbed from a bottle of shampoo. Cosmetic products containing DMDM hydantoin or quaternium-15 don't contain formaldehyde as an ingredient; they contain a compound that slowly generates trace amounts of it, at levels designed to preserve the product without triggering a reaction in most users.

The exception is heated hair-smoothing and hair-straightening treatments — keratin treatments, "Brazilian blowouts," and similar salon services — where the solution is heated and formaldehyde (also sold as formalin or methylene glycol) is released as a gas into the air of an enclosed space. That's a genuinely different exposure route than a rinse-off shampoo, and it's the category both FDA's warning letters and its still-pending proposed rule are actually about — not shampoo or lotion generally.

What's actually restricted

Quaternium-15 is banned outright in the EU, since 2019. Commission Regulation (EU) 2019/831 removed quaternium-15 from the EU's list of permitted cosmetic preservatives and added it to the list of substances prohibited from cosmetics entirely, effective that June. The reason: the cis-isomer of quaternium-15 is classified as a category 2 carcinogen/mutagen/reproductive-toxicant under EU chemical law, and the EU's Scientific Committee on Consumer Safety concluded the ingredient's safety in cosmetics "could not be established." Quaternium-15 carries no such restriction in the US — it's still legal here and still turns up in some shampoo, mascara, and lotion formulas. It's also considered the more sensitizing of the two preservatives on this page, independent of the EU's carcinogen classification.

DMDM hydantoin wasn't banned — it now has to disclose. It remains on the EU's approved-preservative list and is still used in the US at concentrations the Cosmetic Ingredient Review — the industry's independent safety panel — has reviewed and found acceptable at current use levels (around 0.074% in practice). What changed is labeling: Commission Regulation (EU) 2022/1181 lowered the EU's disclosure threshold for any formaldehyde-releasing preservative, DMDM hydantoin included, from 500 ppm down to 10 ppm (0.001%) of released formaldehyde in the finished product. A product above that threshold has to carry a "releases formaldehyde" warning on the label. Manufacturers had until 31 July 2026 to bring existing stock into compliance, so as of now that warning requirement is fully in force across the EU. The US has no equivalent labeling rule.

Hair-smoothing treatments: FDA proposed a ban, but it isn't final. Separately from the preservative question above, FDA proposed in 2023 to ban formaldehyde and formaldehyde-releasing chemicals as ingredients specifically in hair-smoothing and hair-straightening products. That rulemaking has been delayed past several of its own deadlines and, as of this writing, still hasn't been finalized. In the meantime, FDA's actual enforcement tool has been individual warning letters — it has cited two hair-smoothing product makers, Brazilian Blowout and Van Tibolli Beauty Corp., for safety and labeling violations tied to formaldehyde content.

What SafeMama actually recommends

The sensitization concern here is real and specific: people already sensitized to formaldehyde can develop contact dermatitis from repeated exposure to these preservatives, which is exactly why the EU acted on quaternium-15 directly. What it isn't is a cosmetic-dose cancer claim — the carcinogen classification attaches to inhaled formaldehyde gas at high, prolonged exposure, the kind you'd get standing over a heated keratin treatment in a poorly ventilated salon, not from a bottle of shampoo sitting on your skin for two minutes.

If you or your child has a known formaldehyde or preservative sensitivity, check the ingredient list for DMDM hydantoin, quaternium-15, imidazolidinyl urea, or diazolidinyl urea — those are the names to look for on rinse-off and leave-on personal-care products. If you're getting a hair-smoothing or keratin treatment done, ask the salon directly whether the product contains formaldehyde or methylene glycol, and make sure the space is ventilated. That's where the actual inhalation exposure lives, not in your everyday shampoo.

For everyone else, there's no cosmetic-dose evidence requiring you to avoid a product just because it lists DMDM hydantoin. The exposure quiz tracks how often your household reaches for products in this category — a frequency signal for your own reference, not a claim about risk.