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.
Show me some proof
- Liebert, M. A. "Final report on the safety assessment of diazolidinyl urea." J. Am. Coll. Toxicol 9 (1990): 229-245.