Sweat Glands Project
(Note: If you are considering volunteering for this study, scroll down the page for details.)
Funding for this research provided by:
Human eccrine sweat gland density is unique among mammals and primates and enables a remarkable capacity to cool. This sweating ability is intricately linked with major shifts in human evolution, including walking on two legs, bigger brains, near-naked skin, and high levels of physical activity. Surprisingly, we know little about the evolution and diversity of this unique trait. As humans dispersed out of Africa and into novel habitats, sweat gland biology likely changed to suit local environmental conditions. This diversity could be the result of evolutionary processes or environmental effects that occur before adulthood. Indeed, previous researchers proposed that a hot early childhood climate could elicit greater gland activation, resulting in relatively high active sweat gland density in adulthood. This idea remains largely untested. Similarly, the physiological consequences of sweat gland density are unknown. Characterizing diversity in modern human sweat gland density, and assessing the relationship of this measure to heat dissipation and water loss, will elucidate the evolutionary history of this important human trait. Therefore, my project will address the following questions:
1. Does childhood climate explain variation in adult active eccrine gland density?
2. Does geographic ancestry explain variation in active eccrine gland density?
3. What is the relationship between active sweat gland density and ability to dissipate metabolic heat?
To test questions one and two I will recruit up to 160 volunteers from varying childhood climate backgrounds and geographic ancestries, the later determined with genetic ancestry testing. Active sweat gland density will be measured at six body sites via pilocarpine iontophoresis, a method of electro-chemical stimulation, and application of a silicone material to count sweat droplet impressions. I validated these methods in a summer 2018 pilot study.
Testing question three will entail recruitment of at least twenty endurance runners who will exercise under controlled conditions in the room calorimeter at the UMass IALS Human Testing Center. This state-of-the-art facility, one of only twenty-six in the world, enables accurate measurement of metabolic rate and heat dissipation.
Collaborators and Advisors
Dr. Jason Kamilar, Anthropology, University of Massachusetts
Dr. Daniel Lieberman, Human Evolutionary Biology, Harvard University
Dr. Brigitte Holt, Anthropology, University of Massachusetts
Dr. Alex Gerson, Biology, University of Massachusetts
Dr. Michael Busa, Director, UMass Human Testing Center
Jennifer Marino, Kalina Bergmann (2019-present)
Serena Sarage (2017-2018)
Volunteering for Phase 1 of the Study (Gland Counting)
WHO IS ELIGIBLE TO VOLUNTEER:
Any gender/sex, age 18-39, who spent at least the first 5 years of life in one of the following climates:
1) a year-round warm/hot climate, without air conditioning (e.g. India, Central America, southern Florida, Southeast Asia)
2) a seasonal/temperate climate with cold winters and warm summers (e.g., Northeast US and Canada, much of Europe), with air conditioning
3) a year-round mild/cool climate, with or without air conditioning (e.g., highland cities, or ocean climates like parts of England, Pacific Northwest, etc.)
Must be free of sweating disorders or skin disorders covering the body surface.
BEFORE THE DATA COLLECTION:
I'll ask you a few screening questions via phone or email to make sure you qualify. If you've had genetic ancestry testing done through the company 23andMe, I'll ask if you're willing to share some of these results with me. Volunteers less confident in their genetic ancestry may receive a complementary 23andMe test kit, and be asked to share some of the results with the researcher. Then we'll set up a time for you to meet me at the Comparative Primatology Lab, W16 Machmer Hall, at University of Massachusetts for data collection.
THE DATA COLLECTION:
First, I'll let you read an informed consent document, and you'll have the opportunity to ask me clarifying questions about the study. Next, I'll record some body measurements (height, weight, limb lengths, etc.). Then, I'll use mild electrical stimulation and a sweat-stimulating drug to make 6 sites on your body sweat: upper back, upper arm, forearm, torso, thigh, and lower leg. This may entail shaving these locations. (Note: If you are more comfortable with a female researcher touching your skin, this can be arranged.) Once each area is sweating, I'll make an impression of that area with a silicone material for later analysis. I count the droplets in these impressions to quantify how many sweat glands you have. Finally, I tape gauze to these skin sites to collect and weigh sweat. The whole data collection will take about 1.5 hrs. You may work on a laptop or otherwise perform stationary tasks during most of this time.
Volunteering for Phase 2 of the Study (Thermal Testing)
WHO IS ELIGIBLE TO VOLUNTEER:
Male endurance runners age 20-39 years, with an average running volume of at least 4 hours/week in the 8 weeks leading up to testing. Average cycling volume of the past 2 years must not exceed 2 hours/week. Must be locally or regionally-competitive, defined as placing top 5 in a local running race or top 25 in a regional-level race. In the 2 weeks prior to testing, must complete at least 5 training sessions of 60+ minutes in ambient temperatures of at least 86 degrees F. Must be able to conduct heat dissipation testing without wearing a shirt. Must be free of sweating disorders and heart or lung disorders.
BEFORE THE DATA COLLECTIONS
I'll ask you a short series of screening questions over the phone to confirm your eligibility. Then, we'll set up times for each of the 3 data collection visits. Volunteers will receive $50 compensation, prorated after each visit.
THE DATA COLLECTIONS
Visit 1- Comparative Primatology Lab, Machmer Hall W16, UMass. Time: 1.5 hrs. I will count your sweat glands following the procedures described above under "Phase 1".
Visit 2- Human Testing Center, Institute for Applied Life Sciences, UMass. Time: 1.5 hrs. During this visit you will be scanned with an iDXA machine to accurately determine your body fat percentage. After brief familiarization with the metabolic chamber and use of an ear thermometer to monitor your core temperature, you will complete a ~25-40 minute V02-max test on a cycle ergometer in the metabolic chamber. You will NOT need to wear a mask; gases are analyzed in the chamber to determine your maximal oxygen uptake. This is a maximal effort test.
Visit 3- Human Testing Center, Institute for Applied Life Sciences, UMass. Time: 1.5-2 hrs. In this final visit, we will measure how well you dissipate heat while riding the cycle ergometer in warm conditions. You will complete a 1 hour cycling test in the metabolic chamber at a moderate effort (50% of your V02-max). You will provide ear thermometer readings during the test, and researchers will otherwise monitor your safety. In the event of heat illness a cooling protocol will be implemented and medical help will be called. Upon completion of this test, you will move to a warm room and researchers will again count your sweat glands by making impressions of 6 skin areas.