Imidazolidinyl urea is primarily an antibacterial preservative, with very little antifungal activity. It has been widely used in many markets since its introduction in the 1980s.
Imidazolidinyl urea is highly water-soluble and should be added to the product at temperatures below 40°C to avoid decomposition. It retains its activity over a broad pH range, from pH 3 to 9. Typical use concentrations are 0.2–0.5%. The potential for imidazolidinyl urea to release very low levels of formaldehyde is perceived by some to be a disadvantage. Imidazolidinyl urea is permitted globally, with restrictions.

Source: Cosmetic Formulation Principles and Practice - Heather A.E. Benson, Michael S. Roberts, Vânia Rodrigues Leite-Silva, Kenneth A. Walters