J. Cosmet. Sci., 64, 243–260 ( July/August 2013) 243 Infl uence of various environmental parameters on sweat gland activity ROGER L. MCMULLEN, TIM GILLECE, GUOJIN LU, DONNA LAURA, and SUSAN CHEN Department of Materials Science, Corporate R&D, Ashland Specialty Ingredients, Wayne, NJ. Accepted for publication January 31, 2013. Synopsis The choice of environmental conditions when conducting antiperspirant studies greatly affects the quantity of sweat output. Our initial goal in this work was to develop an in-house procedure to test the effi cacy of antiperspirant products using replica techniques in combination with image analysis. To ameliorate the skin replica method, we conducted rheological studies using dynamic mechanical analysis of the replica formula- tion. In terms of sweat output quantifi cation, our preliminary results revealed a considerable amount of variation using the replica technique, leading us to conduct more fundamental studies of the factors that infl uence sweating behavior and how to best design the experimental strategy. In accordance with the FDA’s protocol for antiperspirant testing, we carried out gravimetric analyses of axillae sweating under a variety of environmental conditions including temperature and humidity control. Subjects were fi rst acclimatized in an environmentally controlled room for 30 min, and then placed in a sauna for an additional 30 or 45 min, de- pending on which test we administered. In Test 1 (30 min total in the sauna), the fi rst 10 min in the sauna was another equilibration period, followed by a 20 min sweat production stage. We monitored axillae sweat- ing during the last 20 min in the sauna by gravimetric analysis. At time (t) = 30 min in the sauna, skin replicas were taken and later analyzed using imaging and image analysis techniques. Test 1 was carried out on over 25 subjects, both male and female, from various racial backgrounds. In Test 2, subjects spent 45 min in the sauna after the initial 30-min period in the environmental room. During the 45 min, we obtained gravimetric readings of absorbent pads placed in the axillae. We conducted studies at various temperature and relative humidity settings. We also studied the infl uence of several external parameters on sudoriferous activity. Test 2 was a range-fi nding experiment on two subjects to determine the optimized environmental conditions for the hot room procedure. In addition to the replica and gravimetric techniques, we also mea- sured fl ux density to determine the onset of fi ring of sweat glands to ensure that our environmental precon- ditioning step (30 min in the environmental room) brought subjects to the point that their sweat glands were activated. Although fl ux density measurements are usually carried out to determine transepidermal water loss (TEWL), we found that they can be equally useful for monitoring the onset of sweat production. Thermal infrared imaging experiments were also carried out allowing us to generate full-body images of subjects containing anatomical thermal distribution data with high accuracy. Overall, we conclude that our in-house hot room procedure offers much potential as an effective and cost-effi cient screening tool for narrowing copi- ous antiperspirant formulations to a select few for expensive clinical evaluation. Address all correspondence to Roger McMullen at rmcmullen@ashland.com.
JOURNAL OF COSMETIC SCIENCE 244 INTRODUCTION In Homo sapiens, the principal mode of thermoregulation is accomplished by evaporative cooling that takes place when sweat is secreted from eccrine glands and evaporated from the surface of the skin. Overall, such a process ensures that the body’s core temperature does not signifi cantly rise above 37°C to levels that can lead to heat exhaustion or hyper- thermia. There are about 2–5 million eccrine glands distributed over the surface of the body, which carry out this function (1). In addition, there are approximately 100,000 apocrine glands localized in specifi c regions of the body, most notably the axillae. Al- though apocrine glands secrete substances that eventually break down to malodorous compounds, antiperspirant treatments target eccrine glands that are located in the axil- lae. Therefore, understanding how various external and internal stimuli affect eccrine sweating is of great concern for those involved in antiperspirant technology (2). In addition to thermoregulation, sweating also occurs due to emotional/mental stimula- tion as well as during gustation. In recent years, Wilke et al. provided an updated review covering most aspects of these phenomena (3). We often associate emotional sweating with profuse sweating that occurs in the palms, soles, or axillae (4). Most researchers be- lieve that sweating in these locations during stressful events has evolutionary origins that allowed us to reduce the surface friction of the otherwise high-friction zones of the palms or soles (5). Likewise, secretion of eccrine and apocrine sweat from the axillae during dis- tress would facilitate pheromone signaling to other members of our species. Gustatory sweating occurs in many individuals during digestion and is particularly evident during the consumption of spicy food. Such sweating is normally confi ned to the face, forehead, scalp, and neck (3). Thermoregulatory sweating is affected by many internal and external factors including climatic conditions, diet, physical/mental state, and body posture. The most evident cli- matic factors include temperature, humidity, and dewpoint. At high humidity and dew- point, cooling is less effi cient (6,7). Diet and fl uid intake also play a major role in determining sweating behavior. Not surprisingly, many studies were carried out by military agencies during the 1940s to understand how man could better survive the harsh ele- ments, such as conditions found in the desert (8). Furthermore, it may come as no surprise that clothing is also a critical factor of perspiration. Physical stamina and fi tness form the basis of sweat capacity, and more fi t individuals are likely to be more effi cient sweaters (9). Likewise, the sweat gland apparatus is less active in the elderly, usually beginning around the sixth decade (10,11). Therefore, less fi t and older individuals will tend to overheat much easier. Finally, posture also governs sweating. Whether we are sitting or standing, or even crossing our legs, will infl uence our sweating behavior (7). Posture becomes in- creasingly important during antiperspirant testing when subjects are placed in climate- controlled environments for prescribed periods. In addition, the pH of axillary skin surface fl uctuates depending on the time of day (12). This can have profound implications on the effi cacy of antiperspirant treatments, whose mechanism of action is pH dependent. Overall, all of these factors must be considered when monitoring sweating behavior. Our initial objective in this work was to develop an in-house procedure to test the effi cacy of antiperspirant products using replica techniques in combination with image analysis (13). To better understand the rheological profi le of the replica impression material, we used dynamic mechanical analysis (DMA) to monitor rheological parameters, such as the elastic modulus (E), loss modulus (E), and damping ability (tan δ), as a function of curing
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