Preservative considered weaker than its “cousin” diazolidinyl urea. Most often used with parabens because they work well together. Imidazolidinyl urea is considered a formaldehyde-releasing preservative. Although that sounds scary, the amount of formaldehyde released is well below the limits for safe exposure.
Reference for this information:
International Journal of Cosmetic Science, October 2015, pages 474-478
Skin Pharmacology and Physiology, 2012, pages 236-240