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      Why Does BO Sometimes Smell Like Weed?

      By Nathan A. Thompson

      February 1, 2016

      An artist's impression of BO that smells like weed. Background photo by Nathan Mac via Flickr

      The first time I noticed my BO smelled like weed, I'd just had sex with my girlfriend at the time. She nudged her nose affectionately into my chest. "Hey, you smell like skunk," she said. I sniffed my underarms—she was right, I did.

      Turns out I'm not the only one to have experienced skunky sweat. A Google search revealed several discussions and a Reddit thread where others talked about the phenomenon. Like me, most were baffled. "I smelt my armpit after working out," Reddit user RIP_MAC_DRE told me. "I had been smoking for maybe two or three years at this point and noticed it smelled like weed; I thought it was pretty funny."

      I stayed up all night trawling the internet for answers. But my search brought up little more than the "top answer" on Yahoo Answers, which was just a description of how to wash. Undeterred, and with nothing better to do, I sought out some of the world's most eminent biologists and cannabis experts and distracted them from far worthier business in order to discover, once and for all, why my BO sometimes smells like weed.

      In an original piece of research for VICE, Dr. Matan Shelomi, a researcher at Germany's Max Planck Institute for Chemical Ecology, compared studies that broke down cannabis and human sweat into individual chemicals to see if there were any shared compounds. Out of 233 elements and compounds found in marijuana and nearly 100 in human sweat, 11 matched.

      "It looks like several of the compounds most strongly associated with the distinct aroma of Mary Jane are also found in gym socks," Shelomi told me. "Now all we need are a statistically significant number of sensimilla-scented volunteers and an olfactometry lab that's totally down for whatever."

      Scientific breakthroughs started coming thick and fast. It wasn't long before Dr. Shelomi realized the cannabis smell probably comes from apocrine sweat as opposed to eccrine sweat. Eccrine sweat is clear and watery, and used to cool the body down, while apocrine sweat glands, clumped mainly around the armpits and genitals, activate during sex and times of stress.

      "I remember walking into a [high school] class before giving a presentation and noticing it," Trent, from Kansas, told me. "Eventually, I figured out that my armpit sweat only smells like weed during or before a stressful situation."

      Dr. Shelomi used this as the basis for a potential hypothesis. "If [this] experience holds true for others, then we can narrow down the source of the pot odor to apocrine secretions."

      Another hypothesis, suggested by Dr. Justin Fischedick, a researcher at the Institute of Biological Chemistry at Washington State University, is that aromatic plant chemicals known as terpenoids and terpenes ("terps," for short) are present in the sweat. Plants release terps from their leaves and flowers in order to attract pollinators and repel munching insects. "It seems like people who work out are noticing it quite a bit," Dr. Fischedick told me. "Since [terps] are fat soluble compounds like THC they might be stored in fat cells and get excreted during exercise."

      That covers people who still consume cannabis, but I haven't smoked any weed in years. Perhaps it's because, when I was young, I got through enough of it on a daily basis to permanently alter my body odor. "It wouldn't surprise me if heavy weed intake could alter your smell," Dr. Shelomi told me. "Others online also report having stopped smoking but still reeking of it."

      I didn't want to second-guess an expert, but this just seemed impossible to me. The smell, I figured, is more likely caused by dietary plants that share the same terps as cannabis—an idea mooted in the Reddit discussion. "There can be some similarities between the smells," wrote user LarsHoneytoast. "I think weed, BO, and the lettuce at Subway are all in the same realm of scents."

      Read on Broadly: Sticking Weed in Your Vagina Can Help Your Period Cramps

      I needed to confirm this hypothesis, ideally with the help of someone who isn't named after a breakfast dish. "The smell of cannabis is produced by its terpenes," Dr. Franjo Grotenhermen, the executive director of the International Association for Cannabinoid Medicines, told me. "The consumption of other plants with the same terpenes may result in a similar smell."

      Thanks to weed enthusiasts constantly breeding new strains, there are now a host of cannabis varieties that share terps with many other plants; famous strains like Blueberry Cheesecake and Orange Bud are two notable examples. So there are plenty of plants out there that could make sweat smell like skunk.

      But if cannabis-smelling terps are so common, why don't more people smell like London's Hyde Park on 4/20? Well, BO is not just caused by terps, but also by skin-dwelling bacteria that break down sweat molecules into smaller, volatile compounds that evaporate into smells. Apocrine sweat is also a cocktail of minerals, pheromones, and urea. It seems the skunky smell is down to a particular combination of these composites, making it unusual but not outlandish.

      There could be many more people out there who have the right combination of factors to produce the chronic whiff, even if they don't smoke weed. Naturally, they wouldn't notice because they've never smoked marijuana and so wouldn't know what to sniff for. Or maybe they know what it smells like but just don't care enough to spend all night on Google, before bothering multiple scientists about it.

      All that can be done for now is to trot out the old scientific banality that "more research needs to be done." But at least Dr. Fischedick is up for it. "The only way to find out for sure would be to ask volunteers to smoke a bunch of dank, work out, collect some sweat, and measure it in machines," he told me.

      Anyone interested?

      Follow Nathan Thompson on Twitter.

      Topics: weed, BO, body odour, sweat, cannabis, Nathan Thompson, sweat smells like weed, Dr Matan Shelomi, Dr Justin Fischedick, Dr Franjo Grotenhermen, terps, VICE UK, body odor, drugs, scent, smell, skin, health, science

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