In vitro skin penetration of bronidox, bronopol and formaldehyde from cosmetics

The objective was to evaluate the influence of the formulation in the in vitro transdermal absorption through pig ear skin of three preservatives, bronopol, bronidox and formaldehyde as well as the absorption of formaldehyde from bronopol and dimethyloldimethyl hydantoin (DMDM hydantoin). An aqueous solution, an O/W emulsion and a hydrogel were assayed. Bronidox and bronopol absorption depends on the formulation. The O/W emulsion was the system that least promoted absorption of bronidox while the absorption of bronopol was lower from the hydrogel. The aqueous solution provided maximal transdermal absorption of both preservatives. Moreover, the transdermal absorption of formaldehyde released from bronopol also depends on the formulation, being the aqueous solution the system that allowed greater absorption. Transdermal absorption of formaldehyde, applied directly or released from DMDM hydantoin, is not conditioned by the excipients. The degree of transdermal absorption of all the preservatives tested is low and therefore the concentrations allowed by regulations are safely used. Nonetheless, since formaldehyde was detected in the receptor compartment after a long time exposure to bronopol and DMDM hydantoin it would be important to consider the possibility of limiting the use of these two preservatives to rinse off products as is the case of bronidox.