It may be possible to smell a sexually transmitted disease, a new Russian study says.
In the study, women rated the scent of armpit sweat from men with gonorrhea as less pleasant than the scent of sweat from men without gonorrhea. The women were also more likely to describe the sweat smell as "putrid" if it was from a gonorrhea-infected individual.
The researchers said the men's body odor may have changed as their immune systems responded to the gonorrhea infection.
The women's ability to sniff out infected men could be "part of an evolutionary mechanism ensuring, unconsciously, avoidance of a risky romantic partner," the researchers wrote, in the study published online Dec. 6 in the Journal of Sexual Medicine.
In the study, armpit sweat was collected from 34 Russian men, ages 17 to 25. Thirteen of the men had gonorrhea, 16 were healthy, and five had had gonorrhea in the past, but recovered. The men wore T-shirts with cotton pads in the armpits for one hour, then the pads were placed in glass vials.
The researchers asked 18 healthy women to sniff the vials and rate the pleasantness of the smell on a 10-point scale (with higher scores indicating a more pleasant smell), and also to choose a word from a list to describe the odor (including "putrid," "floral," "vegetable," "woody," "minty" and "fruity").
The women rated the infected men's sweat as less than half as pleasant as the healthy men's sweat. And the women said about 50 percent of men who had gonorrhea had sweat that smelled "putrid," whereas only 32 percent of the healthy men were described as putrid. And while 26 percent of the healthy men smelled "floral," just 10 percent of those with gonorrhea were described that way.
Immune system changes
The researchers speculated that the men's immune systems might be involved because they found a link between the concentration of disease-fighting proteins called antibodies in the men's saliva and how pleasant their sweat smelled to women: the higher the antibody concentration, the lower the score.
Previous studies in animals have found that infecting the mice with parasites or viruses reduces the attractiveness of their smell to female mice.
These studies "call attention to the crucial role of the immune system in the modulation of odor attractiveness resulting from an infection," the researchers wrote.
However, those with STD infections are not at a loss in terms of attracting a mate — the researchers noted that body odor can be improved by deodorants.
Pass it on: Sexually transmitted diseases may make people smell less pleasant to the opposite sex.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.