. 2019 Jul 17;6(3):211–259. doi: 10.1080/23328940.2019.1632145

Table 2.

Common methodological issues.

	Methodological issue	Sweat constituents most affected	Recommendation
Skin cleaning/preparation
Cleaning technique	Skin surface contamination of epidermal origin (desquamation) [227,228,254] Sebum contamination [25,323]	Overestimation (by up to 2–3x) of micronutrient concentrations, but negligible effect on Na and Cl [134,183,227,228] Overestimation of lipophilic compounds abundant in secretions from sebaceous glands (e.g. cytokines, lactate, vitamins, persistent organic pollutants) [25,316,318]	Avoid hand/arm bag technique because of high likelihood of desquamation [228,285] Thoroughly clean skin site when measuring microminerals [228] Avoid sebum contamination by collecting sweat from sites with fewer sebaceous glands and using absorbent pad technique [398]
Timing of collection	Sweat collected at the onset of exercise includes skin surface contamination from residual sweat in ductal lumen [234,399] Sweat collection at onset of exercise (when sweating rate is low) not representative of sweat electrolyte concentrations at steady state sweating rate.	Overestimation (by 1.2-5x) of trace minerals (Fe, Ca, Zn, Mg, Cu) and most other constituents (urea, ammonia, lactate, cytokines, amino acids) compared with later in exercise [228,229,232–234,239,399,400], but negligible effect on Na, Cl, and K [227–229] Sweat [Na] and [Cl] lower at onset of exercise during ramping up of sweating rate.	Begin sweat collection after onset of sweating, i.e. 20–90 min, depending on sweating rate and constituent of interest (shorter for NaCl, longer for trace minerals) to allow flushing of contaminants from lumen and time to reach steady state sweating rate, then clean skin/wipe away sweat from surface prior to collection [228,229,234]
Sweat stimulation
Sauna (steam)	Contamination from steam condensation on skin [25]	Dilution of sweat constituent concentrations from water vapor Bacteria, xenobiotics in steam contaminate skin, sweat [25,401]	Use collection method (Parafilm-M® pouch, absorbent patch) that prevents contamination from surrounding steam
Passive (dry) heat	May not be entirely applicable to sweating response in athletes during exercise (non-thermal stimuli) [55,56]	Potentially all sweat constituents; sweat [Na] and [Cl] lower during passive heat vs. exercise [134,402]	Use if interested in measuring sweat composition in response to environmental heat stress alone (non-athletes). Avoid if interested in understanding sweat constituent losses relevant to exercise [132,137,403,404]
Exercise	Limited to certain collection methods during exercise, especially in athletes in contact sports [132]	All sweat constituents	Use regional method such as absorbent patch for ease of application with athletes and to avoid contamination [156] Collect sweat during exercise representative of training/competition intensities and environmental conditions [132,159]
Pharmacological (e.g. pilocarpine iontophoresis)	Sweat secretion only induced via local cholinergic stimulation of sweat glands, whereas with exercise and/or heat stress other local and central mediators are involved in sweat stimulation [55,56]	Significantly different RSR response, pH, and sweat constituent concentrations (Na, Cl, K, lactate) compared with exercise/heat stress [8,16,134,404–408]	Appropriate for research regarding physiological mechanisms of local control of sweating. Avoid if interested in understanding sweat constituent losses relevant to exercise/whole body heat stress [132,403,404]
Sweat collection
Whole body washdown	Primarily limited to laboratory studies	All sweat constituents	Criterion method because all sweat loss is accounted for and normal evaporation is permitted. Whole body washdown is preferred, especially when quantifying total sweat losses or conducting electrolyte/micronutrient balance studies [134,144,403,409]
Regional methods (in general)	Variability among regional sites [16] Usually not an accurate surrogate for whole-body sweat composition (see Tables 3 and 4)	Up to 2–3.5 fold inter-regional variability for sweat Ca, Mg, Zn, Cu, Fe, Na, Cl [146,147,159,274,286]; inter-regional variability minimal for K [146,159]	Collect sweat from regions that are most representative or highly correlated with whole body across various sweating rates (e.g. forearm for [Na] and [Cl]) [159]
Absorbent patches	Creates microenvironment (increases local skin temperature and humidity) [362] and can alter regional sweating rate compared with uncovered skin [370,410] Absorbent pad may introduce background contamination [149,286]	Potentially any constituent impacted by changes in RSR (Na, Cl, HCO₃) Background Na, Cl, Ca, Mg, Cu, Mn, Fe, Zn reported in patches [149,286]	Limit duration of patch on skin and remove well before saturation [411] Contaminants from the environment cannot penetrate adhesive barrier (Tegaderm^TM) so can be worn during normal activities, including exercise and swimming [412]. Measure and correct for any relevant background in the absorbent pad [149]
Parafilm-M® pouch	Collection is limited to certain regions (back) [228] Not practical for field studies	All sweat constituents	Preferred method for serial measurements of composition (via aspiration of sweat at desired intervals) [413]
Macroduct®/Megaduct	Can only be used on forearm. Not practical for field tests Takes long time (>60 min) to collect enough sweat for analysis (0.5 mL capacity for Megaduct) [414]	All sweat constituents	May be appropriate for use during prolonged heat exposure (>60 min), when not interested shorter duration exercise or serial measurements [414]
Ventilated sweat capsule	Forced ventilation and maintenance of dry skin facilitates higher RSR under the capsule than surrounding skin (at least in a humid/still ambient air) [415,416] Primarily limited to laboratory studies	RSR mostly; not often used to measure sweat composition	Criterion method for RSR; preferred method, especially if maximal RSR representative of compensable environment is desired [417–419]
Arm bag	Particularly susceptible to skin surface contamination due to desquamation and difficulty in cleaning irregular surfaces of hand [228] Microenvironment created by encapsulation which alters RSR [369,420,421]	Overestimation (by 1.5-6x) in sweat Na, Cl, K, Mn, nickel, lead, Cu, Fe, Zn, Ca [228,285,420,421]	Avoid or use modified technique excluding the hand [422]
Scraping methods	Evaporation of water portion of sweat [399] surface contamination by scraping of stratum corneum layer into collection container [399,423]	Overestimation (by ~30%) in all sweat constituent concentrations due to evaporation [183,319] Artificial elevation of concentrations of contaminants of epidermal origin (e.g. by 20x for aminopeptidase) [423]	Avoid
Dripping methods	Evaporation of water portion of sweat and surface contamination [399]	Overestimation in all sweat constituent concentrations due to evaporation [399]	Avoid
Sample storage
Sealing, temperature, duration	Evaporation of water portion of sweat; mold growth	6–42% increase in sweat [Cl] after 3 days and 12–66% increase after 5 days when vials not Parafilm-M®-sealed [424]. When sealed during storage, no change in sweat [Na], [Cl], or [K] when refrigerated, frozen, or at room temperature for 7 days [425].	Seal (e.g. Parafilm-M®) in an airtight tube [424]; refrigerate for up to 1–2 weeks [143,425], or freeze when longer storage durations are necessary
Analytical technique
Laboratory and field	Significant differences between analytical techniques Wide range in ease of use, cost, etc.	Sweat [Na] ion chromatography ≤ ion-selective electrode < flame photometry ≤ conductivity [132,156,372,426–429], 4–30% variation between techniques; not enough information on other sweat constituents	Criterion laboratory-based methods are ion chromatography, inductively coupled mass spectroscopy, flame atomic emission, or absorption spectrometry [430–432] Portable ion-selective electrode acceptable for field analysis [426,429,433]

RSR: regional sweating rate.