De Ligt and colleagues measured systemic absorption of aluminum from a representative roll-on antiperspirant containing aluminum chlorohydrate at 6.25 percent equivalent aluminum in 11 healthy women using a 26Al radiotracer approach with accelerator mass spectrometry. Three topical application scenarios were compared: daily use without shaving, daily use with prior shaving, and no use with no shaving. An intravenous reference dose enabled calculation of the fraction absorbed. This is the original study; a follow-up with higher applied radioactivity was published in 2022 and yielded a more refined estimate.
Key numbers
Fraction absorbed from topical application (Table 2, p. 577; Table 3, p. 579)
Mean F_abs from noncompartmental analysis of blood concentration data: 0.0198 percent, standard deviation 0.0077 percent, range 0.0131 to 0.0354 percent. This estimate is considered less reliable because nearly all blood samples were below the lower limit of quantification.
Mean F_abs from noncompartmental analysis of urine excretion data: 0.0078 percent, standard deviation 0.0064 percent, range 0.0021 to 0.0200 percent.
Using the Norwegian half-lower-limit-of-quantification substitution method (Table 3, p. 579): mean F_abs 0.0094 percent, range 0.000 to 0.0611 percent; conservative worst-case mean 0.0116 percent. This 0.0094 percent figure is cited by the authors as their best estimate (p. 577). The 2022 follow-up at 25-fold higher applied radioactivity revised this downward to 0.00052 percent.
Blood measurements
All blood samples from topical scenarios were below the lower limit of quantification of 0.12 fg per mL, except two samples (one subject under treatment B at 2 hours: 0.13 fg per mL; one subject under treatment C at 6 hours: 0.14 fg per mL). Mean intravenous area under curve: 1,273 plus or minus 466 hours times fg per mL. The authors concluded that practically no aluminum enters the bloodstream following topical application.
Background 27Al in urine
Average background total aluminum in urine: 9.5 micrograms per day, consistent with the German Human Biomonitoring Commission reference value of 15 micrograms per liter (p. 577).
Shaving effect
No statistically significant difference in F_abs was observed between daily-use-with-shaving (treatment B) and daily-use-without-shaving (treatment A) or no-use-with-no-shaving (treatment C), Table 2.
Methods (brief)
Design: randomized crossover. Twelve women enrolled; 14 total with two reserves. Eleven completed all sessions. Three topical scenarios (A: daily use, no shaving; B: daily use, shaving before application; C: no use, no shaving) followed by IV reference dose (D) in four separate occasions. Approximately 100 Bq of 26Al-ACH applied to each axilla (approximately 100 cm squared per axilla). Blood and urine sampled up to 35 days. AMS analysis (1 MV Tandetron AMS, Netherlands). Urine LLOQ: 61 ag per mL; blood LLOQ: 0.12 fg per mL. Total 27Al in urine measured by ICP-MS as background reference. Four-week adaptation period with antiperspirant-free washout before each topical session.
Evidence fitness
This source supports the first human in vivo absolute bioavailability estimate for aluminum from a topically applied antiperspirant, and it established that shaving before application does not significantly increase systemic absorption. The 0.0094 percent best-estimate was adopted by the SCCS in its 2019 opinion and was subsequently revised downward to 0.00052 percent in the 2022 follow-up using 25-fold higher applied radioactivity. Both estimates confirm that dermal absorption is extremely small. This source does not measure aluminum concentrations in finished-market products.
Limitations
Eleven women, single center, Netherlands. Applied radioactivity of approximately 100 Bq was insufficient to quantify blood absorption reliably; the urine estimate is the primary result. The 2022 follow-up substantially revised the absorption estimate downward. The design is applicable only to roll-on formats at 6.25 percent equivalent aluminum; stick, spray, and solid alum forms were not tested. Shaving effect is from a small crossover only; individual variation in skin condition was not measured.
Related evidence
- Antiperspirant (Al-salt, dirty sibling of r9 deodorant)
- Aluminum
- Assessment of dermal absorption of aluminium from a representative antiperspirant formulation using a (26Al)aluminum (Al) microtracer approach: a follow-up study in humans
Update history
No substantive edit history is available in this build. The full commit record is available in git.