Does it actually put formaldehyde in my cream?

Yes, in small amounts and by design. It is not added as formaldehyde; the molecule releases it gradually into the water phase, which is the mechanism by which it preserves the product.

Permitted-preservative lists differ by market and are revised periodically, and formaldehyde-releasing preservatives have been under regulatory review in more than one jurisdiction. Check the current rule where you live rather than a list that may be out of date.

I am allergic to formaldehyde. What should I look for?

Read for the whole family, not just this name: imidazolidinyl urea, diazolidinyl urea, quaternium-15 and sodium hydroxymethylglycinate all release formaldehyde too. If a patch test named formaldehyde, take that list to a dermatologist rather than working it out from labels alone.

Should I avoid it if I am not allergic?

The documented problem is contact allergy, which affects people who have been sensitised. If you have not, the case for avoiding it is weaker than its reputation suggests, and the alternative to a preservative is a product that grows bacteria.

Why can't products just be preservative-free?

They can, if they contain no water — an oil, a balm, an anhydrous powder — or if the pack keeps air and fingers out. Anything water-based on an open shelf needs protecting somehow, and the question is which system rather than whether.

DMDM Hydantoin — Ingredient Guide

How it works

Anything with water in it is a growth medium. A cream is food for the organisms already on the skin, for whatever a finger carries into the jar, and for whatever survived manufacture, and an unprotected product spoils in ways that range from unpleasant to genuinely unsafe. DMDM hydantoin is one of the older answers still in use.

It is a formaldehyde releaser. The formula is not dosed with formaldehyde; it carries a molecule that gives up small amounts slowly into the water phase. Formaldehyde is broadly antimicrobial and particularly effective against bacteria, and the gradual release keeps a low working level present across the product's whole life.

The evidence

That it preserves is not in dispute — decades of industrial use, and a place on permitted-preservative lists in major markets. The argument is about the formaldehyde.

The documented consumer issue is contact allergy. Formaldehyde is a recognised allergen, it sits in the standard patch-test series dermatologists use, and people sensitised to it can react to the releasers as a family. That is a real effect in a minority, and it explains a reputation out of proportion to the concentration.

The other half of that reputation needs separating out. Formaldehyde's carcinogen classification rests on inhalation exposure, largely occupational. Whether trace release from a leave-on cosmetic carries the same risk is a different question resting on different evidence, and not one this page can settle. The allergy evidence is specific and solid; the leap from an inhalation classification to a face cream is not.

Suitability

Unremarkable for most people at the levels used to preserve a product
Avoid if a patch test has named formaldehyde or a formaldehyde releaser
The family also includes imidazolidinyl urea, diazolidinyl urea, quaternium-15 and sodium hydroxymethylglycinate
Exposure is lower in a rinse-off than in a leave-on
Contact allergy is a reaction to the ingredient, not evidence about whether the product works

Concentration

No figure is given here on purpose. Both the maximum permitted level and the concentration above which a product must be labelled as releasing formaldehyde are set in regulation, differ between markets and have been revised more than once. A number quoted from memory would read as authoritative and could be a year out of date, so check the current rule where you live. The general point holds: preservatives work at fractions of a percent, which is why they sit near the end of a list.

Conflicts & combinations

Nothing notable clashes with it among common actives. It is routinely paired with a chelating agent, which binds the metal ions microbes need and makes the whole system harder to defeat — ordinary design rather than a special combination. Worth knowing: a preservative system is built as a whole, so a product marketed as preservative-free is usually anhydrous, protected by its packaging, or preserved by something not on the consumer's list of names to avoid.