Diazolidinyl Urea

When a formula needs a bodyguard against the invisible troublemakers, this is one of the preservatives that steps in. Diazolidinyl Urea helps keep products from being spoiled by bacteria, yeast, and mold, which is exactly why it shows up in everything from creams to cleansing products. It is especially appreciated in formulas that contain lots of water, because water is basically a five-star hotel for microbes if you do not invite a preservative to the party.

Now for the part that gives it a somewhat dramatic reputation: it is part of the formaldehyde-releasing preservative family. That means it can slowly break down and release tiny amounts of formaldehyde over time. Formaldehyde itself is a well-known preservative, but also a common allergen and irritant, so this is where the debate starts. The good news is that the released amount is very small, and the Cosmetic Ingredient Review concluded in 2006 that Diazolidinyl Urea is safe as used in cosmetics at concentrations below 0.5%, with formaldehyde release staying under the recommended limit of 0.2%.

Still, “safe as used” is not the same as “everyone’s skin will love it.” A study from 1990 found that at concentrations up to 0.4%, it could act as a mild cumulative irritant, meaning repeated exposure may make sensitive skin grumpier over time. That is why people with eczema, a history of preservative allergy, or very reactive skin often prefer to steer clear of formaldehyde releasers altogether. If your skin is not easily offended, though, there is usually no reason to panic just because you spot it on an ingredient list. In cosmetics, preserving the product is not a side quest; it is part of keeping the whole formula safe and usable.

An antimicrobial preservative that helps your products not to go wrong too quickly. It works especially well against bacteria, specifically gram-negative species, yeast, and mold.

Somewhat controversial, it belongs to an infamous family of formaldehyde-releasers. That is, it slowly breaks down to form formaldehyde when it is added to a formula. We have written more about formaldehyde-releasing preservatives and the concerns around them at Dmdm Hydantoin, but do not get too scared, those are more theories than proven facts.

As for Diazolidinyl Urea itself, a study from 1990 writes that at concentrations up to 0.4%, it was a mild cumulative skin irritant, but the CIR (Cosmetic Ingredient Review) reviewed it in 2006 and found that, in concentrations of <0.5%, it is safe as used, as the amount of formaldehyde released will be smaller than the recommended limit (of less than 0.2%).

All in all, it is up to your personal decision and skin sensitivity.