ENVIRONMENTAL PARAMETERS ON SWEAT GLAND ACTIVITY 255 mentioned that “he would not sweat much today” because he felt cold from spending much of the day in a cool working environment. Because the subject was historically known as an excellent and predictable sweater, it was hypothesized that his conditioning and subsequent sweating response may have been somewhat subdued by his recent envi- ronmental history. In addition, to minimize or to begin to appreciate the intrusion of circadian and seasonal variations on the sweating processes of a single subject within multiple studies, fl ux density measurements were undertaken to investigate the infl uence of the environmental history on the effectiveness of the fi nal acclimatization process. Hence, an exploratory instrumental method was developed for gauging a subject’s uncanny and accurate “feeling” that he/she is ready or not ready to sweat. Closed-chamber evaporimeters (e.g., AquaFlux AF200) are devices typically used to mea- sure TEWL, which is the steady-state fl ux density of water vapor diffusing through the skin barrier (17). Meaningful TEWL measurements are typically accomplished in cool and dry ambient environments to diminish the impact of ambient humidity and exces- sive insensible perspiration on the quality of the measurement however, since our inter- ests involve monitoring the physiological response to thermal stress (i.e., not TEWL), cumulative fl ux density profi les, as a function of time and elevated heat index, are relevant toward understanding the advent of perspiration processes (18). For Subjects 1 and 2, fl ux density readings (n = 3) were recorded at 0, 30, and 60 min of acclimatization (30.5°C and 36.5% RH) after initial equilibration in cool (6.3°C and 66% RH), or warm (24.1°C and 28% RH) settings. At each time point, readings were taken at three different zones of the mid-volar forearm, always starting with Zone 1 and ending with Zone 3. Zone 1 was closest to the wrist, Zone 3 was closest to the elbow, and Zone 2 was sandwiched between Zones 1 and 3. Table III conveys the average number of fl ux density maxima (n = 3) visible in the fl ux density vs. time plots, skin surface water loss (SSWL, n = 3), and fl ux density (n = 3). The reported average fl ux density refl ects the averaged steady-state fl ux density, or the timed-out (80 s) fl ux density, which are inher- ently larger than the subject’s TEWL if infl uenced by insensible sweating (19). The SSWL is a combination of the quantity of water on the surface of the skin and the instru- ment transient, which is the water absorbed from the air during transfer of the instru- ment from zone to zone. Because no visible perspiration was seen, it is assumed that the number of fl ux maxima and the variation in the average fl ux readings are attributable to the pulsing infl uence of active eccrine glands (20,21). When a subject is equilibrated in the cool environment, a single fl ux maximum, which is related to the SSWL, and a steady- state fl ux density, which is related to TEWL, are present (e.g., 6.3°C data for Subjects 1 and 2) in the fl ux density vs. time plot. Exposure to warmer pre-equilibration tempera- tures, or to longer acclimatization times, causes a thermoregulatory response by the sub- ject and the TEWL results are subsequently confounded by the infl uence of increased, steady, yet insensible, perspiration. Eventually, if the conditions warrant, eccrine activity intensifi es and the number of fl ux density maxima within a single measurement period increases (e.g., 24.1°C pre-equilibration and 60 min acclimatization data, Figure 5 and Table III). The visible pulsing effect in the evaporimetry profi le is assumed to be the sum- mation of effl ux from the asynchronous fi ring of several active eccrine glands within the confi nes of the 38.5-mm2 measurement orifi ce. For brevity, Table III summarizes only the data from the 0- and 60-min marks of fi nal acclimatization (30.5°C and 36.5% RH), after pre-equilibration at the cool and warm conditions. Both subjects exhibited a single fl ux maximum, and a typical TEWL-like

JOURNAL OF COSMETIC SCIENCE 256 steady-state fl ux response at t = 0 of acclimatization after pre-equilibrating in the cooler environment. Further, after 30 min acclimatization, both subjects saw a rise in average fl ux density (+3.1–3.5 gm−2 h−1), and the average number of fl ux maxima increased to 2.5 for Subject 2, yet only advanced to 1.3 for Subject 1. Similar trends are seen at the 60-min mark. The discernible increase in fl ux for Subject 2, which is refl ected in the large re- ported standard deviation, was caused by a spike in the eccrine fl ux as the trial approached the 80 s mark (i.e., the experiment timed-out). Hence, due to sporadic sudorifi c activity, some of the fl ux density readings were not evaluated at steady state. Pre-equilibration in a warm environment introduced similar, but more exaggerated, increases in fl ux density. In addition, both Subjects 1 and 2 showed increases in the number of fl ux density Figure 5. Average fl ux density vs. time profi les during acclimatization after 15 min pre-exposure to the 6.3°C environment (n = 3). SSWL and fl ux density were recorded at (A) t = 0 min, (B) t = 30 min, and (C) t = 60 min of acclimatization. The inset shows the determination of SSWL and TEWL from fl ux density vs. time profi les.