Final Report on the Safety Assessment of Methenamine

Abstract

Methenamine is a biocide that is used in cosmetic eye make-up preparations at concentrations of less than 1%. Methenamine, following oral administration, undergoes hydrolysis and generates formaldehyde. Methenamine is rapidly absorbed from the intestinal tract and excreted mostly unchanged in the urine. A single oral dose of 20 g/kg Methenamine did not cause mortality in rats. No untoward signs of toxicity were observed in either subchronic or chronic studies. Methenamine was slightly irritating to the skin of rabbits. In ocular studies it was mildy irritating. In animal assays, Methenamine was a sensitizer when tested at a concentration of 25%, but not at 0.2%. It was neither an irritant nor a sensitizer to humans at 0.1%. In a number of teratologic and reproductive studies, no teratogenic effects attributable to Methenamine were observed. Methenamine was a mutagen in Drosophila melanogaster but not in other in vitro mutagenicity assays. Methenamine did not show any carcinogenic activity, either alone or when nitrite was included in the drinking water of the test animals. Methenamine is judged to be safe for non-aerosolized cosmetic products at a concentration not to exceed 0.16%. At this concentration, the released formaldehyde concentration will not exceed 0.2%.