Imidazolidinyl urea is an antimicrobial preservative used in cosmetic products. It is used to protect products from spoilage caused by yeast, bacteria or mold included in the formulas. It is a formaldehyde releaser and one of the most widely used preservatives in the world, according to the National Cancer Institute.
Some people have a contact allergy to imidazolidinyl urea causing dermatitis. Such people are often also allergic to diazolidinyl urea.