Asparagus—the perennial, springtime vegetable—is native to Europe, northern Africa, and western Asia. The world’s largest asparagus producer is China, and its top importers are the U.S., the European Union, and Canada. Farmers have extended its harvest season from February to November by growing asparagus under tunnels and regulating their environments because we want it all the time. There's even a National Asparagus Festival every June in Oceana County, Michigan, the “asparagus capital of the world.”

Judging by that, it would stand to reason that a great many of you know where this conversation is heading—down the toilet. Asparagus tastes great and is widely available, but another cool thing about it is that it makes your pee smell weird. I know that makes me sound 12-years-old, but I only mean that when something so common and also nutritious has such a potent effect on a not-for-polite-conversation bodily byproduct, it’s almost so playfully enigmatic I can’t stand it.

I'm not alone in my curiosity. Asparagus-eaters have noticed that the vegetable affects pee smell for centuries. Scottish mathematician and physician John Arbuthnot wrote in 1731 that “asparagus … affects the urine with a foetid smell.” Early thinkers had differing opinions on whether or not they liked asparagus pee: Marcel Proust wrote that asparagus “transforms my chamber-pot into a flask of perfume,” while Benjamin Franklin wrote in 1781 that “a few stems of asparagus eaten, shall give our urine a disagreeable odour.”

Asparagus pee is fascinating to me, your disgusting and intrepid reporter, for many reasons: it’s a mystery who produces it and who can sense it, the smell itself is impossible to describe, and whether that odor is good or bad is a polarizing topic. 

One thing most scientists agree on: asparagusic acid (which, as its name suggests, is only found in asparagus) is metabolized into sulfur-containing compounds, like methanethiol—the most prominent smell in your asparagus pee. These chemicals usually have a low boiling point, becoming smelly gases at room temperature, and hitting us in the face with that familiar odor.

But who makes asparagus pee, and who smells it?

According to Professor John H. McDonald in the biology department at University of Delaware, a 1980 study found that all participants produced asparagus pee, but only some smelled it. A 1987 study found the opposite; only some participants produced asparagus pee, but everyone could smell the difference. And a 1989 study found that 103 French people all produced asparagus pee and all of them identified it as stinky.

"It’s a mystery who produces it and who can sense it, the smell itself is impossible to describe, and whether that odor is good or bad is a polarizing topic."

So what is the truth? Does making and smelling asparagus pee vary everywhere except France?

“It is clear that in addition to variation in excretion, there is also variation in the ability to smell the compounds,” McDonald wrote. “It is not clear whether this variation is continuous, or whether people can be clearly divided into smellers and non-smellers.” In other words, the ability to both create and smell asparagus pee varies.

In my reading, it’s been difficult to find words that describe the smell of asparagus pee. Some say it’s mildly sulfuric, but that’s an adjective I’ve come to associate with rotten eggs, and my asparagus pee doesn’t smell like rotten eggs. Is part of asparagus pee’s enigmatic appeal that the smell is so unique that it’s impossible to describe with comparisons? When you say asparagus pee, someone either knows what’s up, or they don’t.

I also learned about white asparagus in my research—a type of asparagus that doesn’t produce chlorophyll; growers cover the spears in dirt so that they’re not exposed to light. On Quora, user Kelly Martin wrote, “There is actually some reason to believe that white asparagus contains more asparagusic acid (the component in asparagus that cases “asparagus pee”) than the more ordinary green asparagus, and no reason to believe that it contains less or none at all.”

I don’t know what qualifies Kelly Martin to speak so authoritatively about white asparagus’ effect on pee, but I thought that if white asparagus could make the smell more pronounced, I might be able to glean more insight into describing a more potent smell. Unfortunately, white asparagus is hard to find fresh (at least around me), so the easiest solution was buying it canned from my local grocery store. The stalk from out of the can tasted less “grassy” and earth-y than green asparagus. When it came to the sniff test, it was the same old asparagus pee, and I couldn’t find new words to describe it.

I spoke to Marc Herskowitz, a physician who specializes in urology, and asked if there were other things people consumed that might change their urine as drastically as asparagus does. “No, not at all,” he replied. He explained that some diseases, like UTIs, can make urine smell funny and kind of “fishy,” and that chemotherapy can leave a distinctly chemical odor.

When I prodded him to describe the odor, we both kept defaulting to, “You know...asparagus pee smell!” I mentioned that one of my friends liked the smell, and asked if he had a personal or professional opinion on it; he responded that he “always found it to be a little off-putting.” When I told him Marcel Proust loved it, he just laughed.