Dr. Belsito noted that imidazolidinyl urea had been reviewed by the CIR and the panel issued a final report in 1980 which concluded that it was the opinion of the expert panel that, based on the evidence at hand, it considered it relevant and Accumulated in a reasonable manner, the cosmetic ingredient imidazolidinyl urea is safe when incorporated into cosmetic products in amounts similar to those currently marketed.
After reviewing summaries of studies published since the initial imidazolidinyl urea final report, the panel unanimously concluded that the safety evaluation should not be revisited and the original conclusions should not be changed.
Formaldehyde emission
The amount of formaldehyde released by diazolidinyl urea and the other seven formaldehyde-releasing preservatives depends on the substrate, pH, time and (mainly) temperature. 2 The release effect also varies with cosmetics, products such as hand sanitizers release more formaldehyde, shampoos and body washes than products such as toothpaste, nail polish and perfume.
constituent stock
About 30 - 40% of imidazolidinyl ureas have been characterized as allantoin, (4-hydroxymethyl-2,5-dioxo-imidazolidin-4-yl)-urea and 1-(3,4-bis-hydroxymethyl-2 ), 5-dioxo-imidazolidin-4-yl)-1,3-bis-hydroxymethyl-urea.3 The remainder was considered to be a polymer of allantoin-formaldehyde condensation products.
Another characterization study of imidazolidinyl urea from three different sources (dissolved in aqueous solution, from patch test material and from cosmetics) found that the composition was allantoin, (4-hydroxymethyl-2,5 -dioxo-imidazolidine-4-yl)-4-urea, (3,4-bis-hydroxymethyl-2,5-dioxo-imidazolidine-4-yl)-urea and (3-hydroxymethyl-2,5-dioxo -imidazolidine-4-yl)-urea. The first two urea components are also common in diazolidinyl ureas and may be a possible cause of cross-reactivity between the two different urea components.
cosmetic use
In the EU, imidazolidinyl urea is listed as a preservative in Annex V with a maximum concentration limit of 0.6% in ready-to-use preparations. 5
The Australian Government's National Industrial Chemicals Notification and Assessment Scheme (NICNAS) concluded that imidazolidinyl urea should be classified as a sensitization hazard by skin contact. 6 Recommended concentration cut-off 1%.
non-cosmetic use
Imidazolidinyl urea and other formaldehyde-releasing agents have been investigated as therapeutic corneal and scleral tissue cross-linking agents. 7
genotoxicity
Imidazolidinyl urea (0 - 10,000 μg/plate) in water was not mutagenic, with and without metabolism, in the Ames test using Escherichia coli WP28uvr A and Salmonella typhimurium strains TA 98, TA 100, TA 1535 and TA 1537 activation. Furthermore, imidazolidinyl urea (up to 10.0 μg/ml) in water did not significantly increase the proportion of cells showing chromosomal aberrations in Chinese hamster ovary cells, with or without metabolic activation.