I’ve written a version of this sentence hundreds of times for Outside: “The layer is made from wool, so of course it doesn’t stink.”

There’s some truth to that, for sure. According to Keith Anderson, vice president of marketing at Ibex, wool has a lot of characteristics that naturally fight odors. “The fatty acids that live within the wool absorb and lock in that [smelly] microbe and hold on to it—literally locking it up within the fat itself—so that the microbe can’t multiply and emit odor,” he says.

But how long can you really go before a wool layer starts to smell as bad as a synthetic one? To find out, I put on Trew’s Superlight Nuyarn merino pocket tee and lived in it, full-time, for as long as I could (that is, until my wife took notice). This is the same test I ran last summer on a Patagonia shirt treated with Polygiene—silver threads that also combat funkiness. Read on to see how the wool stacked up.

Field Notes

Day 1
I began with a clean slate when I woke up. I washed the shirt and took a shower, then skipped deodorant. After ten hours of working at my kitchen table, I took a 3.15-mile run with about 700 feet of elevation gain in 55-degree heat. At the end, there was a sweat stain on my chest, and my pits were soaked. After grocery shopping, I ate dinner and went through another round of work. My wife, Sarah, went to bed before I finished, so I smelled my own pits before hopping into bed. Verdict: Zero stink.

Day 2
After some computer work, I took another 3.15-mile run at 12:30 and got soaked in the rain. The shirt smelled like wet livestock until it dried (about 20 minutes). I stunk because I hadn’t showered or used deodorant since yesterday, but the shirt wasn’t holding on to my odor. My wife didn’t say anything about my stink when I got into bed. If she did notice, she was too polite to say anything.

Day 3
This was a rest and travel day. I skipped the shower and deodorant again and ate nothing but beef jerky and peanuts while driving six hours to Davis, California. I finished the day with spicy drunken noodles. No shower. No deodorant. Since I was traveling for work, I had to depend on my own smell test. Result: I was perfectly fine with the smell of the shirt in my hotel bed.

Day 4
Still no shower or deodorant before I walked all over Davis for a reporting project—a little more than seven miles total—in temperatures ranging from the mid 60s to low 70s. By early afternoon, the shirt pits were soaked. My armpits themselves smelled like rancid milk. To test the shirt, I took it off, buried my head in the pits and inhaled. Nothing. I put it back on and went to bed.

Day 5
I broke up my computer work day in Davis with a 50-minute run in 72-degree heat. That afternoon, I finally broke down and took a shower. Once again I skipped deodorant. When I smelled the shirt, I noticed a faint smell in the left armpit, but it wasn’t bad. Putting the shirt on my clean body didn’t feel like a chore.

Day 6
No shower or deodorant before I drove six hours home. That afternoon, I went for a four-mile hike in jeans and 75-degree heat. I didn’t fully sweat through the shirt, but the pits were soaked and my body smelled. There was no reaction from my wife when I settled into bed with the shirt on.

Day 7
I decided to crank up the sweat level in hopes that I could stop wearing the shirt. With no shower or deodorant, I ran a little more than six miles with 1,100 feet of elevation gain in 70-degree heat. I managed to soak the arms, chest, and part of the back, and my BO took on an oniony smell. The shirt smelled a little, but that smell mostly dissipated once it dried. I took a shower to wash off my own stink and to help wash off some poison oak. I was in bed by 9:30 with no reaction from my wife.

Day 8
By this point, I was really sick of wearing the shirt. I did a 30-minute TRX workout at 7:00 p.m. to end my computer workday. Afraid that my wife wouldn’t notice yet again, I asked her to smell the shirt. “Oooh, that’s good,” Sarah said while pressing her nose in. “That is real good. The pits aren’t even a thing, and you are not a nonstinky dude. You have a healthy man sweat about you.”

Day 9
I woke up afraid that the test would last forever, so I took the shirt off, washed it, and took a shower.

The Takeaway

I want to reemphasize my wife’s point: I often smell worse than other people, so I was highly impressed with how long the shirt stayed fresh. There’s no doubt I could have made it rot, but I’m guessing that might have taken a full two weeks.