The Truth About DMDM Hydantoin Hair Loss

If you’ve been perusing TikTok or Reddit (or know someone who has), you may have heard that an ingredient in certain shampoos, conditioners, and other cosmetic products, known as DMDM hydantoin, causes hair loss.

If you’re noticing thinning hair, it can definitely be rattling to think that your hair care products are to blame. But as you know, you can’t take everything you hear on social media or see on the world wide web at face value — there are currently no scientific studies connecting DMDM hydantoin to hair loss.

The ingredient does have potentially concerning ties to formaldehyde and allergic contact dermatitis, though. So what exactly is DMDM hydantoin and what’s it doing in these products in the first place? Most importantly, should you avoid using it? Keep reading to find out.

DMDM hydantoin, sometimes written as glydant on product labels, is a preservative with antimicrobial properties. It helps to prevent the growth of mold and other fungi, yeast, and harmful bacteria.

While many people try to avoid preservatives in their food by buying organic products, preservatives are actually important and necessary in cosmetics and hair and skincare products — particularly those that contain water (which is most of them).

Water can be a breeding ground for bacteria and mold, especially in a warm, humid environment like a bathroom.

Preservatives in personal care products, such as shampoos, conditioners, cleansers, moisturizers, and makeup, help keep them safe to use for longer.

DMDM hydantoin will not make your hair look thicker or shinier. In fact, it has no benefits for hair specifically. The benefit of DMDM hydantoin is limited to the fact that it's a potent and low-cost preservative. It’s also white and odorless, so it blends easily into products without changing its color or smell.

If shampoos and conditioners didn’t have preservatives, the pink or black mold that you commonly see in the corners of tubs or showers could grow inside the bottles where you won’t see it.

Enter preservatives, like DMDM hydantoin. Other common preservatives are phthalates, parabens, and certain alcohols (all of which can potentially cause irritation). Even “natural” products contain preservatives like ethanol or benzyl alcohol.

Here’s where things get tricky. DMDM hydantoin releases small amounts of formaldehyde, especially when exposed to heat. It’s actually supposed to do this. That’s the mechanism that keeps these types of preservatives (known, aptly, as formaldehyde releasers) doing their job killing microorganisms.

The exact amount of formaldehyde varies depending on temperature, formula and pH of the product, and other factors.

This sounds alarming. After all, formaldehyde often conjures up images of embalming liquid, paint, or glue — not things you’d want to put on your scalp.

But keep in mind that formaldehyde is also naturally occurring in some foods, including bananas, potatoes, and cauliflower. Yet those are all perfectly safe to eat.

Formaldehyde can cause skin irritation in some people, though. That’s why legislation in both the USA and the European Union (EU) limits the concentration of formaldehyde allowed in personal care products to 0.2 percent. The quantity of DMDM hydantoin required for preserving a product should never exceed that limit.

If you go into the depths of any online forum, you’ll find anecdotes of people who claim DMDM hydantoin caused their hair to fall out. There are even class-action lawsuits against certain brands filed by people who say they experienced hair loss after using products with DMDM hydantoin.

But here’s the thing — no scientific evidence shows that DMDM hydantoin causes hair loss. Generally, shampoo is in contact with hair quite briefly and DMDM is not readily absorbed by skin.

With that said, if you have an allergy to formaldehyde, the ingredient could cause a severe allergic reaction on the scalp that eventually leads to hair loss.

So if you’re noticing hair loss and are unsure why, it’s unlikely — but not impossible — that your shampoo or conditioner is the culprit, even if it contains DMDM hydantoin.

You can learn more about behaviors that potentially cause hair loss in our guide.

DMDM hydantoin is almost certainly not the reason you’re losing hair, but you may still wonder if it’s causing other damage.

While the ingredient is considered safe in the low concentrations mentioned earlier, preservatives including DMDM hydantoin are listed as common allergens in cosmetics by the U.S. Food and Drug Administration (FDA).

Additionally, research suggests that DMDM and other formaldehyde-releasing products could cause contact skin irritation in some people — especially those with pre-existing formaldehyde allergies.

A study from 1998 found that people who were sensitive to formaldehyde were at an increased risk of developing dermatitis and itching after using products containing DMDM hydantoin.

The side effects of DMDM hydantoin are typically related to formaldehyde rather than DMDM itself.

There isn’t a ton of research on DMDM hydantoin specifically, but there is a lot on formaldehyde exposure. Research shows that even short-term exposure to formaldehyde can cause wheezing, watery eyes, nausea, and skin irritation — especially in people with a sensitivity to formaldehyde.

Below, we’ve broken down some potential side effects of formaldehyde exposure, and therefore DMDM.

Allergic Contact Dermatitis

We mentioned that a reaction to DMDM hydantoin is most likely to occur in people who are allergic or sensitive to formaldehyde, and it feels important to note that is not a rare sensitivity.

Research shows that allergic contact dermatitis (a type of eczema) as a result of formaldehyde is most common in women with eczema on the hands or the hands and face.

When the skin barrier on the hands is damaged, formaldehyde from cosmetics, toiletries, and other cleaning products can more easily penetrate the skin.

Occupational Allergic Contact Dermatitis

Occupational allergic contact dermatitis is also common and mostly affects the hands. It is particularly common in hairdressers and healthcare workers who use creams and soaps containing formaldehyde releasers. Formaldehyde sensitization tends to develop over time with continued use of products with those ingredients.

Folliculitis

Folliculitis is a type of contact dermatitis that can appear anywhere you have hair follicles. If you have a sensitivity to an ingredient, including DMDM hydantoin, it’s possible that you’ll experience folliculitis on the scalp.

This condition generally looks like small red or white bumps on the scalp. While DMDM hydantoin isn’t known to cause hair loss, it could cause folliculitis, which could in turn potentially cause hair loss.

Folliculitis decalvans is a severe type of folliculitis that can cause hair loss if left untreated. The condition causes a kind of scalp inflammation known as granulocytic inflammation, which destroys the hair follicle and damages the scalp.

Over time, this can potentially cause scarring alopecia, a permanent form of hair loss in which the follicles stop producing new hair and are instead replaced by scar tissue.

Cancer

We know it can be scary to read, but cancer is mainly a risk for people who are exposed to high levels of formaldehyde through their jobs (like embalmers or carpenters).

The National Toxicology Program classifies formaldehyde as a carcinogen, but there is currently no evidence linking the small amounts of formaldehyde in personal care products to an increased risk of cancer.

The FDA also warns of the following side effects of using hair smoothing products (so not specifically DMDM) that release formaldehyde when heated:

• Eye problems or irritation

• Nervous system problems including headaches and dizziness

• Respiratory tract problems including sore or scratchy throat, cough, or wheezing)

• Nausea

• Chest pain

• Vomiting

• Rash

Formaldehyde releasers are found in as much as 20 percent of cosmetics in the USA. It’s always smart to do a patch test before using products containing DMDM hydantoin — especially if you have a formaldehyde allergy or sensitive skin.

To perform a patch test, put a small amount of product on your forearm, wait at least an hour, and note any reactions.

In a 2020 study analyzing the results of people who underwent patch testing at Massachusetts General Hospital between 2007 and 2016, only 2.5 percent of patients tested positive for allergic contact dermatitis from formaldehyde. For context, the top allergen identified was nickel, with 19.8 percent of the subjects testing positive for it.

Even though that research indicates most people won’t have a contact allergy, some states, including California, Maryland, and Washington have banned the use of formaldehyde in personal care products starting in 2025.

If you’re reading this, you’re probably noticing some hair loss or thinning. But if the fix isn’t swapping your products for ones without DMDM hydantoin, what can you do?

Below, we review some proven treatment options so you can take action.

Finasteride

Finasteride is proven to slow hair loss and stimulate new hair growth in men experiencing male pattern baldness, which is caused mainly by a genetic sensitivity to the male hormone dihydrotestosterone (DHT). Studies show that this prescription medication can reduce DHT by as much as 90 percent.

Minoxidil

Unlike finasteride, minoxidil doesn’t work specifically on hormones, making it a good option for many different types of hair loss, including telogen effluvium (hair loss caused by stress or injury) and traction alopecia (hair loss caused by overly tight hairstyles).

The over-the-counter medication is a vasodilator, increasing the diameter of blood vessels (which supply the scalp with oxygen and blood flow) as well as the diameter of the hair follicle itself.

While it works differently than finasteride, it’s also a good choice for male pattern baldness.

We offer minoxidil liquid solution or minoxidil foam at Hims. Following an online consultation with one of our healthcare providers, oral minoxidil (in a chewable form) could also be an option — particularly if you don’t want the upkeep of a topical product.

Minoxidil and Finasteride Together

Research shows that combining minoxidil and finasteride is more effective than either alone. Our topical finasteride and minoxidil spray is an easy way to use the two ingredients together.

Hair Loss Shampoo and Conditioner

Just as a shampoo or conditioner probably doesn’t cause hair loss, no shampoo or conditioner can totally stop or reverse hair loss.

But shaking up your shower haircare routine can make a difference in your hair’s volume and thickness.

Our thickening shampoo is made with saw palmetto, a botanical ingredient that can slow hair loss and modestly improve hair regrowth.

Our volumizing conditioner (the sidekick to our volumizing shampoo) lifts hair at the root, making it look fuller, and our thickening conditioner with niacinamide helps build keratin, an essential protein for hair health.

None of our haircare products contain DMDM hydantoin (or sulfates, parabens, phthalates, or silicones, for that matter).

DMDM hydantoin probably doesn’t cause hair loss, but there are other potential side effects and flags you should be aware of.

• Safety and Efficacy: DMDM hydantoin is an effective preservative in hair care products, preventing a product from spoiling and extending its shelf life by reducing microbial growth. Despite concerns, lawsuits, and statewide bans, there is currently no scientific evidence linking it directly to hair loss (though it could potentially cause folliculitis, which is linked to hair loss in some cases).

• Potential Side Effects: While generally safe in low concentrations, DMDM hydantoin releases small amounts of formaldehyde, potentially causing skin irritation or allergic reactions. The side effects of DMDM hydantoin are actually side effects of formaldehyde exposure, and allergic contact dermatitis is a fairly common DMDM hydantoin side effect, particularly in those with a sensitivity to formaldehyde.

• Check the Ingredient List: If you have sensitive skin, experience scalp irritation when using a certain haircare product, or know you have an allergy to formaldehyde, always check the ingredient list on product labels for formaldehyde-releasing preservatives, including DMDM hydantoin — which may also be listed as glydant.

For more information on what may be causing your hair loss, check out our guides to temporary hair loss and medications that can cause hair loss.