Imidazolidinyl urea

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Imidazolidinyl urea is an antimicrobial preservative used in cosmetics. It is chemically related to diazolidinyl urea which is used in the same way. Imidazolidinyl urea acts as a formaldehyde releaser.


Some people have a contact allergy to imidazolidinyl urea causing dermatitis[1]. Such people are often also allergic to diazolidinyl urea.


Imidazolidinyl urea was poorly characterized until recently and still has a wrong CAS structure assigned to it. New data show that the hydroxymethyl functional group of the imidazolidine ring is attached to the carbon, not the nitrogen atom [2]:

Imidazolidinyl urea (correct new structure) Imidazolidinyl urea (erroneous old structure)
Correct new structure Erroneous old structure


Imidazolidinyl urea is produced by the chemical reaction of allantoin and formaldehyde in the presence of sodium hydroxide solution and heat. The reaction mixture is then neutralized with hydrochloric acid and evaporated:

2 Allantoin + 3 H2C=O → Imidazolidinyl urea

Commercial imidazolidinyl urea is a mixture of different formaldehyde addition products including polymers[2].


  1. Review of toxicological data (NTP NIEHS)
  2. 2.0 2.1 Lehmann SV, Hoeck U, Breinholdt J, Olsen CE, Kreilgaard B. (2006). "Characterization and chemistry of imidazolidinyl urea and diazolidinyl urea". Contact Dermatitis. 54 (1): 50–58. doi:10.1111/j.0105-1873.2006.00735.x. PMID 16426294.

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