Diazolidinyl Urea
What It Is
Diazolidinyl urea is a synthetic preservative in the formaldehyde-releasing preservative class (CAS 78491-02-8). It is a white to off-white powder, marketed under the trade name Germall II. Diazolidinyl urea is structurally related to imidazolidinyl urea but releases more formaldehyde per unit weight. It functions as a broad-spectrum antimicrobial preservative in personal care products.
Common Uses
Diazolidinyl urea is used in shampoos, conditioners, lotions, creams, makeup, and hair care products. It is typically used at concentrations of 0.1%-0.5%. Like imidazolidinyl urea, it has limited antifungal activity and is commonly paired with a paraben to achieve full broad-spectrum preservation. Diazolidinyl urea is less common than imidazolidinyl urea in the marketplace but remains in use across numerous product formulations.
How It Works
Diazolidinyl urea releases formaldehyde through hydrolysis in aqueous solution. The released formaldehyde provides antimicrobial activity by cross-linking microbial proteins. Diazolidinyl urea releases approximately twice as much free formaldehyde as imidazolidinyl urea at equivalent concentrations, which makes it more effective against bacteria but also increases formaldehyde exposure to the user.
Its stronger formaldehyde release gives it better standalone antibacterial activity than imidazolidinyl urea, but antifungal activity remains limited. The paraben co-preservative pairing is standard for both products.
Safety and Regulation
The CIR Expert Panel concluded that diazolidinyl urea is safe at concentrations up to 0.5% when formulated to limit formaldehyde release (CIR, 2000). The EU Cosmetics Regulation permits it with the standard FRP labeling requirement for formaldehyde content above 0.05%.
Diazolidinyl urea is a documented contact allergen, with positive patch-test rates in the 1%-3% range in consecutively tested dermatology patients. Its higher formaldehyde release rate compared to imidazolidinyl urea may contribute to a somewhat higher sensitization potential, though the clinical data do not show a dramatic difference between the two.
Why Natural Flower Power Does Not Use It
Natural Flower Power does not use diazolidinyl urea in any product.
Diazolidinyl urea is excluded under our prohibition on all formaldehyde-releasing preservatives. Its higher formaldehyde release rate compared to imidazolidinyl urea makes it particularly unattractive within the FRP class. Our BIT-based preservation system provides both antibacterial and antifungal activity without releasing formaldehyde and without requiring a paraben co-preservative.
Related Ingredients
Imidazolidinyl urea is the most closely related FRP, with lower formaldehyde release. DMDM hydantoin and quaternium-15 are other FRPs. Formaldehyde is the active substance released. Benzisothiazolinone (BIT) is the preservative Natural Flower Power uses instead.
Sources
- Cosmetic Ingredient Review (CIR). "Final Report on the Safety Assessment of Diazolidinyl Urea." International Journal of Toxicology, vol. 19, Suppl. 3, 2000, pp. 1-20.
- European Commission. Regulation (EC) No 1223/2009. Annex V.
