PRESERVATIVE
DMDM Hydantoin
- preservative
A preservative that works by slowly releasing small amounts of formaldehyde; some brands avoid it for that reason.
- products in our library
- 111
- of researched products
- 2%
- on the label, in our shampoos
- usually #15
- most common in
- Shampoo
- in water
- Water-soluble
At a glance
Four things worth knowing about how this ingredient behaves on hair.
How much of it is left on hair between washes.
What it takes to get it off the hair again.
What it is in the formula to protect.
Where it sits on the labels we have, in the category it appears in most.
| Property | Level | Out of |
|---|---|---|
| Buildup risk | Low | 1 of 5 |
| Rinse-out behaviour | Rinses clean | 5 of 5 |
| Role | Keeps water-based formulas | 4 of 5 |
| Prominence | Secondary | 2 of 5 |
What it does for a formula
What DMDM Hydantoin does
The general function first, then how the role changes by product type where we have researched it.
Works by releasing a trace of formaldehyde over time; a common avoid-list entry.
Water alone removes it, so it does not accumulate between washes.
Charge
Charge is not recorded for this ingredient.
Solubility
Rinses out with water alone, so it does not build up on hair between washes.
Where it appears
Where it appears
One row per product category in our library: how many products list it, what share of that category that is, and where it typically sits on the label.
| Product type | How common | Typical position on label ? |
|---|---|---|
Shampoo
30 products
|
secondary · #15 | |
Conditioner
17 products
|
secondary · #15 | |
Styler: curl cream
12 products
|
secondary · #14 | |
Leave-in
10 products
|
secondary · #15 | |
Mask / treatment
9 products
|
secondary · #23 | |
Styler: gel
7 products
|
supporting · #8 | |
Styler: mousse
5 products
|
secondary · #15 | |
Co-wash
3 products
|
secondary · #18 | |
Styler: paste
3 products
|
secondary · #9 | |
Heat protectant
2 products
|
secondary · #15 |
11 more product types
| Product type | How common | Typical position on label ? |
|---|---|---|
Scalp treatment
2 products
|
secondary · #29 | |
Styler: edge control
2 products
|
secondary · #13 | |
Finisher: end oil
1 product
|
secondary · #14 | |
Finisher: oil
1 product
|
secondary · #26 | |
Finisher: serum
1 product
|
secondary · #11 | |
Finisher: shine spray
1 product
|
secondary · #12 | |
Relaxer
1 product
|
secondary · #25 | |
Styler: lotion
1 product
|
supporting · #6 | |
Styler: refresh spray
1 product
|
secondary · #26 | |
Styler: smoothing cream
1 product
|
secondary · #25 | |
Styler: volumizer
1 product
|
secondary · #11 |
| Product type | Products | Share of category | Median position | Earliest position | Band |
|---|---|---|---|---|---|
| Shampoo | 30 | 2% | 15 | 7 | secondary |
| Conditioner | 17 | 2% | 15 | 7 | secondary |
| Styler: curl cream | 12 | 5% | 14 | 8 | secondary |
| Leave-in | 10 | 1% | 15 | 6 | secondary |
| Mask / treatment | 9 | 2% | 23 | 13 | secondary |
| Styler: gel | 7 | 3% | 8 | 6 | supporting |
| Styler: mousse | 5 | 2% | 15 | 8 | secondary |
| Co-wash | 3 | 3% | 18 | 7 | secondary |
| Styler: paste | 3 | 2% | 9 | 7 | secondary |
| Heat protectant | 2 | 1% | 15 | 13 | secondary |
| Scalp treatment | 2 | 1% | 29 | 19 | secondary |
| Styler: edge control | 2 | 5% | 13 | 7 | secondary |
| Finisher: end oil | 1 | 13% | 14 | 14 | secondary |
| Finisher: oil | 1 | 0% | 26 | 26 | secondary |
| Finisher: serum | 1 | 1% | 11 | 11 | secondary |
| Finisher: shine spray | 1 | 1% | 12 | 12 | secondary |
| Relaxer | 1 | 25% | 25 | 25 | secondary |
| Styler: lotion | 1 | 3% | 6 | 6 | supporting |
| Styler: refresh spray | 1 | 3% | 26 | 26 | secondary |
| Styler: smoothing cream | 1 | 1% | 25 | 25 | secondary |
| Styler: volumizer | 1 | 1% | 11 | 11 | secondary |
We have not researched differences by product type yet. The reading below comes from where it sits on the labels in our library.
Position footprint
Every listing in our library, by position on the label.
| Positions | Zone | Listings |
|---|---|---|
| 1-3 | Leading | 0 |
| 4-8 | Supporting | 15 |
| 9-15 | Secondary | 46 |
| 16-25 | Lower | 28 |
| 26+ | Trace | 22 |
How to read this
US labelling rules put ingredients above 1% in descending order of amount; below 1% they may be listed in any order.
So position tells you about relative amount only above that line, and we never convert a position into a percentage.
Why it matters to shoppers
What seeing this ingredient tells you, what it does not, and the limits of our own method.
- a broad-spectrum preservative
- a product that keeps over its shelf life
- a rinse-clean feel
- an exact safety score (we do not publish one for any ingredient)
- how a finished product performs, which depends on the whole formula, not one line of it
- the exact percentage in a bottle, because label position never converts into a number
- a secondary formaldehyde-releasing preservative, listed below the main ingredients in our shampoos
- it was on the printed ingredient list of every product we counted (we read labels, not marketing copy)
- that the product would be better without one
- that a product is right or wrong for you
We do not publish safety scores or hazard grades. Where a regulator has published a restriction or a use condition, we state it and cite it; otherwise we describe what the ingredient does and stop.
Why some people avoid it
A preservative that works by slowly releasing small amounts of formaldehyde into the product, which is what keeps it from spoiling.
Formaldehyde is a recognised contact allergen and is classified as a human carcinogen by inhalation. Rinse-off hair products are a skin-contact exposure, not an inhalation one, so the live question for a shopper is contact allergy: these preservatives are a common cause of allergic contact dermatitis on the scalp and hairline.
Where regulators stand: Permitted in the US. The EU caps the released-formaldehyde level and requires products above the threshold to be labelled. Dermatology patch-test panels include them, which is how a person usually finds out they react.
Peer-reviewed human evidence
Commonly paired with
The ingredients that most often appear alongside this one in our library. We leave out the near-universal ones, because they pair with everything and tell you nothing.
- Propylene Glycol · 46
- Disodium EDTA · 43
- Methylisothiazolinone · 31
- Iodopropynyl Butylcarbamate · 30
- Sodium Chloride · 30
- Cetrimonium Chloride · 30
- Methylchloroisothiazolinone · 29
- Dimethicone · 29
- Cocamidopropyl Betaine · 29
- Tetrasodium EDTA · 24
The number beside a name is how many products in our library list both.
These ingredients tend to appear together to carry the formula and let it dry, keep the formula stable, and improve feel after rinsing.
Found in these products
The most prominent placements first. The badge is the position on that product’s own ingredient list.
Curl Keeper · Styler
Ultimate Frizz Control
#6 on the label · $4.33/oz
Lottabody · Styler
Concentrated Setting Lotion
#6 on the label · $0.31/oz
Suave · Leave-in
Kids Silly Apple Detangler Spray
#6 on the label · $0.50/oz
African Pride · Shampoo
Dream Kids Olive Miracle Detangling Moisturizing Shampoo
#7 on the label · $0.38/oz
Design Essentials · Styler
Sleek Edge Control
#7 on the label · $3.78/oz
L'Oreal Paris · Styler
Studio Line Above It All Invisi Gel Max Hold
#7 on the label · $0.73/oz
Suave · Leave-in
Kids Detangler Spray Berry Awesome
#7 on the label · $0.50/oz
Suavecito · Styler
Suavecita Pomade
#7 on the label · $5.21/oz
Urban Hydration · Co-wash
Jamaican Castor Oil Co-Wash & Conditioner
#7 on the label · $0.59/oz
VO5 · Conditioner
Moisture Milks Moisturizing Conditioner - Strawberries and Cream
#7 on the label · $0.32/oz
Kenra Professional · Styler
Styling Gel 17
#8 on the label · $3.17/oz
Kenra Professional · Styler
Volume Mousse Extra 17
#8 on the label · $2.63/oz
See all 111 products in the library that list DMDM Hydantoin
Identity
What this entry is, and what our references call it.
DMDM Hydantoin
- CAS 6440-58-0
- PubChem 22947
- formaldehyde releaser
- dmdm hydantoin
For your hair?
Whether DMDM Hydantoin matters for your hair depends on your hair.
111 products in our library list itWhat this ingredient does, and where it sits on the labels we have researched.
A verdict on any product that contains it, and never a safety grade.
We do not physically test your hair. Everything above comes from the ingredient lists in our library and from published references. The consultation is what turns it into a plan.
References
Sourced Backed by a manufacturer or regulatory source.
This ingredient
- Manufacturer or regulatory PubChem : Compound identity: CID 22947, CAS 6440-58-0, C7H12N2O4 · accessed 2026-08-28
How this page was made
- Every number above is counted from the ingredient lists in our own product library: 111 of 6816 researched products list this ingredient. Nothing on this page is written per ingredient.
- The dots are levels, not scores. Each one comes from what kind of ingredient it is (its chemical class, charge and solubility) or from where it sits on the labels we have.
- US labelling rules put ingredients above 1% in descending order of amount; below 1% they may be listed in any order. Position tells you about relative amount only above that line, and we never convert a position into a percentage.
- The prominence bands (leading, supporting, secondary) are the same ones the product pages use to read a single label, applied here to the median position across a category.
- We do not publish safety scores or hazard grades. Where a regulator has published a restriction or a use condition, we state it and cite it; otherwise we describe what the ingredient does and stop.
- Identifiers and references appear only when a published source is attached to this entry. Without one, we leave the row out rather than fill it in.
- This is cosmetic information, not medical advice, and nothing here diagnoses or treats a health condition.
- Entry last updated 2026-09-22. Product-page methodology: the product library.
