Assessment of dermal absorption of aluminium from a representative antiperspirant formulation using a (Al)Al microtracer approach: a follow-up study in humans.

de Ligt R, Westerhout J, Grossouw D, Buters TP, Rissmann R, Burggraaf J, Windhorst AD, Tozer S, Pappa G, Wall B, Bury D, Mason DR, Vaes WHJ

A follow-up study was performed in 12 healthy women to evaluate systemic exposure to aluminium following topical application of a representative antiperspirant formulation under real-life use conditions (part A) and to assess the local fate of topically applied aluminium by taking additional tape strips and skin biopsies (Part B). A simple roll-on formulation, containing the maximal possible radioactive dose, was prepared with [Al] aluminium-labeled chlorohydrate (ACH). The microtracer of [Al] was used to distinguish aluminium from the natural background, using accelerator mass spectrometry. [Al] aluminiumcitrate was administered intravenously to estimate the dermal fraction absorbed. Despite the 25-fold increase of the topical dose compared with the previous study, only 12 blood samples gave results above the lower limit of quantitation (0.118 fg/mL). The most reliable estimates of the dermal fraction absorbed are derived from noncompartmental analysis with the urine data. By using the intravenous dose to normalize the urinary excretion to 100% bioavailability, the best estimate of the fraction absorbed of [Al] from a topical application of [Al]-aluminium-labeled chlorohydrate in an antiperspirant formulation was 0.00052%. Part B of the study demonstrated that the majority of the aluminium in the formulation remained associated with the external layers of the skin without penetration through the skin.