The mechanism of eccrine sweat pore plugging by aluminium salts using microfluidics combined with small angle X-ray scattering

Abstract

Aluminium salts are widely used to control sweating for personal hygiene purposes. Their mechanism of action as antiperspirants was previously thought to be a superficial plugging of eccrine sweat pores by the aluminium hydroxide gel. Here we present a microfluidic T junction device that mimics sweat ducts, and is designed for the real time study of interactions between sweat and ACH (Aluminium Chloro Hydrate) under conditions that lead to plug formation. We used this device to image and measure the diffusion of aluminium polycationic species in sweat counter flow. We report the results of small angle X-ray scattering experiments performed to determine the structure and composition of the plug, using BSA (Bovine Serum Albumin) as a model of sweat proteins. Our results show that pore occlusion occurs as a result of the aggregation of sweat proteins by aluminium polycations. Mapping of the device shows that this aggregation is initiated in the T junction at the location where the flow of aluminium polycations joins the flow of BSA. The mechanism involves two stages: (1) a nucleation stage in which aggregates of protein and polycations bind to the wall of the sweat duct and form a tenuous membrane, which extends across the junction; (2) a growth stage in which this membrane collects proteins that are carried by hydrodynamic flow in the sweat channel and polycations that diffuse into this channel. These results could open up perspectives to find new antiperspirant agents with an improved efficacy.

Developing a new device for continuously recording, in vivo, the excretion rate of sweat (perspiration) in humans

“…Since the late 1970s, it has been generally accepted that aluminum salts form a superficial plug at the canal ostia. However, the details and mechanisms of the process that lead to the formation of the plug were only recently explained through a combination of sophisticated technologies . In brief, these two converging studies clearly confirm that ACH acts as a plug‐forming concrete material.…”

Minerals in biology and medicine

“…52 Aluminium Chloro Hydrate (ACH), another antiperspirant, can form polycationic species such as 3Al 13 and 3Al 30 with molecular weights reaching over 5000 Da in solutions around pH 4. 53 Sodium zirconium cyclosilicate (ZS-9) is a non-absorbed cation exchanger that selectively binds potassium in the intestine, and used for treatment of chronic hyperkalaemia at doses of 2.5-10 g per day administered with meals. 54 It is a nonabsorbable mineral which selectively binds K + (and NH 4 + ) in exchange for Na + and H + in the whole gastrointestinal tract.…”

Real time observation of the interaction between aluminium salts and sweat under microfluidic conditions

“…For example, most proteins naturally present in human sweat or constitutive of sweat pore walls are anionic at the pH of sweat 18 , and can thus aggregate in the presence of aluminium polycations. This electrostatic aggregation is considered to be the basis of the antiperspirant effect of ACH [19][20][21][22] .…”