Why Is DMDM Hydantoin in My Shampoo—and Is it Safe?

A person shampoos their hair from the back

Asya Molochkova / Stocksy

Complicated name, equally complicated heat in the comments section. 

If you’ve been paying attention to the recent controversies on #HairTok, a quick scroll will show videos warning about the dangers of using DMDM hydantoin in your shampoo. Some users claim that the ingredient can lead to hair loss or even cancer, citing class action lawsuits against certain brands that used DMDM hydantoin as evidence. 

Of course, one can’t take every single TikTok trend as fact. So to clear things up once and for all, we spoke to cosmetic chemists Krupa Koestline and Ginger King and board-certified dermatologist Kim Nichols, MD, FAAD.

Meet the Expert

  • Krupa Koestline is a clean cosmetic chemist who has worked with brands including Kopari, Tower 28, and Chantecaille. She is the founder of KKT Consultants
  • Ginger King is a cosmetic chemist and the founder of the product development consulting service Grace Kingdom Beauty.
  • Kim Nichols, MD, FAAD, is a board-certified dermatologist and the founder of NicholsMD of Greenwich, SkinCeuticals SkinLab by NicholsMD, and NicholsMD of Fairfield.

We asked the experts to outline the purpose of DMDM hydantoin in shampoo formulas, possible side effects, and whether or not you should toss any products that contain the ingredient. Keep reading to find out what they had to say.

DMDM Hydantoin

Type of Ingredient: Preservative

Main Benefits: Helps to prevent the growth of bacteria in shampoos, conditioners, and some cosmetics

Who Should Use It: Those who are comfortable using products that contain the ingredient, or haven’t had a negative reaction to DMDM hydantoin

Works Well With: Formulas prone to bacteria growth 

Don’t Use With: King notes that DMDM hydantoin shouldn’t be paired with other formaldehyde donors like quaternium-15.

What Is DMDM Hydantoin?

DMDM hydantoin is a preservative often used "to keep pathogens like bacteria and mold at bay in beauty products,” Koestline says. And as Nichols tells us, it can be found across categories: "Commonly known as glydant, [DMDM hydantoin] is used in the formulation of many products across the skin and hair care industries, including but not limited to shampoo, conditioner, soaps and cleansers, makeup, and moisturizers."

The controversy? While it does prevent microbial growth, according to King, it can release formaldehyde under high temperatures. “The material is meant to preserve the product—in general, it is a safe ingredient, and the way it releases formaldehyde could be formula dependent,” she says. “There is a limit for formulators to use 0.6 percent at the very maximum in products, and with rinse-off products like shampoos and conditioners, the ingredient is less likely to affect the skin or scalp.” While less likely, irritation isn’t completely out of the question. Even though the maximum limit isn’t a super-high percentage, Koestline notes that DMDM hydantoin is also a common allergen as listed by the FDA.

Benefits of DMDM Hydantoin

DMDM hydantoin doesn’t pack any benefits for your skin or hair—the benefits are more geared toward preventing microbial growth in the products that use it. "It's used mainly because of its antimicrobial properties—it helps to prevent the growth of harmful bacteria, which in turn aids in preserving and prolonging the shelf life of skin and hair care products," says Nichols.

“Hair products often require preservatives as they are usually stored in showers or bathtubs,” Koestline further explains. “The contact [they have] with water, as well as the warm, humid environment [they are stored in], are conducive to bacterial and fungal growth.”

Side Effects of DMDM Hydantoin

With DMDM hydantoin being a common allergen, some may have an adverse reaction to formulas that contain the ingredient, even in quantities less than 0.6 percent. King notes that common reactions are itching or swelling on the area where it’s applied. “Some people may get contact dermatitis as a result,” Koestline says. “There was a concern on TikTok as people were associating it with hair loss, but there doesn't seem to be a link between hair loss or hair thinning and DMDM hydantoin.” It is worth noting, she adds, that itchiness or irritation on the scalp can lead to hair shedding.

Of course, there’s the whole aspect of DMDM hydantoin releasing formaldehyde, which is a toxic ingredient used in creating plywood, adhesive, insulation, and, probably most unsettlingly, as an embalming agent. But would you be surprised to learn that formaldehyde is also naturally occurring? It appears in fruits and vegetables like apples, pears, onions, and cauliflower, which your body breaks down into carbon dioxide. “To put formaldehyde exposures from DMDM hydantoin in personal care products into perspective, the tiny amount of formaldehyde released from DMDM hydantoin is about equivalent to the amount of formaldehyde naturally occurring in one medium-sized apple or pear," Joseph Cincotta, Ph.D., vice president of Color Wow R&D told us. "It has also been used in preservatives for over 50 years and is found in IVs to counter any bacteria.”

"I recommend that my patients do a small patch test or trial of any products formulated with DMDM hydantoin because it is a common culprit of eczema flare-ups and allergic contact dermatitis," says Nichols. "However, DMDM hydantoin is considered generally safe for use overall."

How to Use DMDM Hydantoin

Although many brands that follow clean guidelines choose to leave DMDM hydantoin out of their formulations, Koestline notes that some brands will include it, as it is effective at preventing bacterial growth and, in small quantities, is believed to be safe. That said, you’ll want to look out for DMDM hydantoin among products you’d normally keep in your bathroom. Certain shampoos, conditioners, face washes, and skincare products may use the ingredient to prevent mold from growing in a humid environment with fluctuating temperatures.

The Final Takeaway

Whether or not you choose to use formulas that contain DMDM hydantoin is entirely a personal decision, but if you’re experiencing discomfort or irritation from a product formulated with the ingredient, discontinue use immediately. While it is generally regarded as safe, many brands are recognizing the concerns consumers have and are either leaving it out of their products entirely or reformulating products that once contained the controversial ingredient. It's your call, but considering the wide range of shampoos that eliminate it— and the fact that it doesn’t pack any benefits for your hair or scalp—it’s easy enough to opt-out if you so choose. 

Article Sources
Byrdie takes every opportunity to use high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial guidelines to learn more about how we keep our content accurate, reliable and trustworthy.
  1. Babar N, Kim M, Cao K, et al. Cosmetic preservatives as therapeutic corneal and scleral tissue cross-linking agentsInvest Ophthalmol Vis Sci. 2015;56(2):1274-1282.

  2. Toxicology NRC (US) C on. Effects on Humans. National Academies Press (US); 1980.

  3. Nowshad F, Islam MdN, Khan MS. Concentration and formation behavior of naturally occurring formaldehyde in foodsAgriculture & Food Security. 2018;7(1):17.

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