Diazolidinyl Urea

Diazolidinyl Urea is a formaldehyde-releasing preservative used at low concentrations (typically ~0.1–0.5%), but it is a well-documented cause of allergic contact dermatitis on patch testing, especially in patients with eczema or impaired skin barriers. While many tolerate it, sensitized individuals can experience significant reactions and the risk is heightened with cumulative exposure across multiple products. Given its established sensitization potential and patient-safety concerns in reactive skin populations, it warrants a notable irritancy score. Safety Notes: In commercial cosmetics, diazolidinyl urea is most often used as a formaldehyde-releasing preservative at low levels around 0.05–0.2% in leave-on creams/lotions and similar or slightly higher levels in rinse-off cleansers to meet antimicrobial preservation targets while minimizing sensitization risk. Higher-strength consumer products (especially some cost-optimized or higher-water-content emulsions and hair/body rinse-off products) have been observed up to about 0.5%, which aligns with common industry maximum-use guidance and safety assessments for this preservative. Use is constrained by irritation/sensitization considerations and regulatory/safety review recommendations, so OTC products typically do not exceed ~0.5%.