Ellison (2002) compared testosterone levels in men ages 15 to 60 in four populations: Lese farmers in the Congo, Tamang farmer-herders in Nepal, and Ache hunter-gatherers in Paraguay, and Americans in the Boston area. The researchers found that American men had the highest testosterone when young (average 335 in the 15- to 29-year-old age group) and a 29% decline to 238 in the 45- to 60-year-old age group. Congolese young men were 286 and declined 14% to 247. Nepalese young men were 251 and declined 10% to 225. Ache young men were 197 and declined 2% to 192. In the 45-60 age group all four groups had similar testosterone levels. American young men had 70% more testosterone than Ache young men. It appears that American young men have unusually high testosterone levels, which decline to normal levels with age. This may be because American high schools and colleges put hundreds, even thousands, of young men and women in close contact. In contrast, a hunter-gatherer may only occasionally meet an unrelated person of the opposite sex.
Additional studies have investigated testosterone and aging in Japan
men of Kenya, Ariaal
men of Kenya, and Zimbabwe
had 42 women using oral contraceptives and 39 women not using oral contraceptives wear t-shirts for one day. The researchers noted where each woman was in her menstrual cycle. 31 men and 12 women then smelled the t-shirts and rated the sexual attractiveness. The men rated the sexual attractiveness of the t-shirts worn by women not using oral contraceptives as highest around ovulation. No correlation between sexual attractiveness to men and ovulation was found in the women on oral contraceptives. No correlation was found in the women's ratings for any of the women's t-shirts. This study suggests that oral contraceptives may contribute to men's low testosterone because women on oral contraceptives don't produce the pheromones signaling ovulation that boost men's testosterone.
Many non-human animal studies have found increases in testosterone in males after exposure to females' bodily secretions such as urine or vaginal fluid. Most of these studies have been with rodents such as mice, rats, and hamsters. A few studies have used monkeys. (See the bibliography in Roney and Simmons (2012)
for these references.)
Miller and Maner (2010) reported two studies in which young men were exposed to women's sweat. In the first study, four young women (18- and 19-year-old college students) wore t-shirts during ovulation, and then a second t-shirt during their luteal phase (far from ovulation). The women were not on hormonal contraceptives; showered with unscented soaps; refrained from using perfumes, deodorants, and antiperspirants; avoided odor-producing foods (e.g., chili, garlic, pepper, vinegar, asparagus); and didn't use drugs. The women wore the t-shirts while sleeping for three nights, then put the t-shirts into freezer bags and gave them to the experimenters, who then froze the t-shirts. Within six days the t-shirts were defrosted for the experiment. 37 young men (18- to 23-year-old college students) smelled one t-shirt each. Testosterone was measured via saliva before the experiment and fifteen minutes after smelling a t-shirt. The results showed a very small (0.5%) increase in testosterone after smelling the t-shirts worn during ovulation; and a more substantial (18%) decrease in testosterone after smelling the luteal phase t-shirts.
In Miller and Maner's second study, eleven young women (18- and 21-year-old college students) wore t-shirts during ovulation, and then a second t-shirt during their luteal phase. A third set of t-shirts was not worn by anyone. 68 young men (18- to 23-year-old college students) smelled one of the three t-shirts. In this study, testosterone dropped for all three groups. The ovulation group dropped 7%; the luteal phase group dropped 20%; and the control group dropped 17%. This study also asked the men to rate odor; the results were that men preferred the odor of the t-shirts worn around ovulation.
Roney and Simmons (2012) had young women (mean age 19) wear gauze pads taped under their arms for five minutes after they had "broken into a sweat" while walking around the University of Texas, Austin psychology building on a hot day. The gauze pads were then frozen and sent to the University of California, Santa Barbara. The researchers then placed the gauze pads into bottles of water. Additional new gauze pads were placed in other bottles of water. Young men (mean age 20) participated twice, about a week apart, in which they smelled the bottles. Saliva was collected twice before and four times afterwards (15, 30, 45, and 60 minutes afterwards). No change in testosterone was found.
These results suggest that women's sweat isn't an effective way to boost men's testosterone. However, our study will differ from the above studies in several ways:
- Our male subjects will be middle-aged, low-testosterone men. The above studies used young men who are in daily contact with many young women and presumably have high testosterone levels.
- The above studies looked at short-term testosterone changes (15 minutes to 60 minutes after exposure). We intend to test long-term testosterone changes after a month of exposure to women's sweat. Again, this would likely show null results with college students who are in daily close contact with many young women, but could show positive results with middle-aged men.
- Our methods for collecting and preserving women's sweat will be different. T-shirts are too big to handle so we'll use scrunchies. If we get enough volunteers we could compare gauze pads to scrunchies. Freezing makes shipment difficult so we'll use desiccant, vacuum storage, and UV sterilization. If we get local volunteers we'll run a group that gets fresh scrunchies delivered the same day to test whether preservation diminishes effectiveness. We could even ask one group of men to take partner dance classes for a month.
- Our methods for delivering women's sweat will be different. Roney and Simmons (2012) may have proven only that smelling sweat diluted in water eliminates effectiveness, i.e., each gauze pad may have had less than 0.1 grams of sweat, and if each bottle had 100 grams of water, the dosage may have been diluted 1000x or even 10,000x. Miller and Maner's male subjects smelled the women's t-shirts but didn't physically contact the women's sweat. Our plan is for male subjects to slightly dampen the scrunchies, then rub the scrunchies on their upper lips. This should increase the dosage of sweat by a factors of thousands. (Don’t worry, Miller and Maner's second study found that young men rated ovulating young women’s sweat as attractive. And we all remember that a woman’s hair can smell like heaven.)
- If we have enough male subjects, and willing female subjects, we could include an experimental group in which the women send a picture of themselves along with their scrunchies, or correspond via e-mail. It's possible that the combination of visual and olfactory cues will be more powerful than scent alone.
Ellison, P., Bribiescas, R., Bentley, G., Campbell, B., Lipson, S., Panter-Brick, C., Hill, K. (2002) Population variation in age-related decline in male salivary testosterone. Human Reproduction, 17:12, 3251-3253. Free download: http://humrep.oxfordjournals.org/content/17/12/3251.full
Attractiveness of women's body odors over the menstrual cycle: the role of oral contraceptives and receiver sex
Kuukasjärvi, S. , Eriksson, P., Koskela, E., Mappes, T. , Nissinen, K., & Rantala, M. (2004) Attractiveness of women's body odors over the menstrual cycle: the role of oral contraceptives and receiver sex. Behavioral Ecology, 15:4, 579-584. Free download: http://beheco.oxfordjournals.org/content/15/4/579.short
Roney, J., & Simmons, Z. (2012) Men Smelling Women: Null Effects of Exposure to Ovulatory Sweat on Men's Testosterone. Evolutionary Psychology, Vol. 10 Issue 4, p703-713. Free download: http://www.epjournal.net/wp-content/uploads/EP1070...
Miller, S. & Maner, J. (2010) Scent of a Woman: Men’s Testosterone Responses to Olfactory Ovulation Cues. Psychological Science February 2010 vol. 21 no. 2 276-283 doi: 10.1177/0956797609357733 http://pss.sagepub.com/content/21/2/276
(Download costs $35)