Assessment of Dermal Absorption of Aluminum from a Representative Antiperspirant Formulation Using a 26Al Microtracer Approach

A clinical pharmacokinetic study was performed in 12 healthy women to evaluate systemic exposure to aluminum following topical application of a representative antiperspirant formulation under real‐life use conditions. A simple roll‐on formulation containing an extremely rare isotope of aluminum (26Al) chlorohydrate (ACH) was prepared to commercial specifications. A 26Al radio‐microtracer was used to distinguish dosed aluminum from natural background, using accelerated mass spectroscopy. The 26Al citrate was administered intravenously (i.v.) to estimate fraction absorbed (Fabs) following topical delivery. In blood samples after i.v. administration, 26Al was readily detected (mean area under the curve (AUC) = 1,273 ± 466 hours×fg/mL). Conversely, all blood samples following topical application were below the lower limit of quantitation (LLOQ; 0.12 fg/mL), except two samples (0.13 and 0.14 fg/mL); a maximal AUC was based on LLOQs. The aluminum was above the LLOQ (61 ag/mL) in 31% of urine samples. From the urinary excretion data, a conservative estimated range for dermal Fabs of 0.002–0.06% was calculated, with a mean estimate of 0.0094%.