Why Does Asparagus Make Your Pee Smell Funky?

iStock/ehaurylik

You’re by no means the first person to notice the unique aroma we’ll call “asparagus pee.” In fact, it was first described in 1735 in an essay by John Arbuthnot, in which he describes asparagus as something which ‘affects the urine with a fetid smell.’ And since Arbuthnot’s essay, modern science has helped us to gain some understanding of why this particular vegetable has this odd effect.

Turns out it has something to do with a chemical known as asparagusic acid.

When we eat asparagus, our body breaks down the asparagusic acid into smaller compounds that contain sulfur. And much like the sulfur-containing compounds in garlic and skunk spray—the odor is quite strong! What’s more, those molecules are ‘volatile,’ meaning that they change form, becoming a gas at room temperature. So basically, when we pee them out, they convert into a gas and go right up our nose. The process happens rather quickly too. In some cases, the odiferous compounds have been detected in the urine of people who ate asparagus as recently as 15 minutes earlier!

And yet asparagus does not affect everyone the same way. In fact, more people can’t smell asparagus pee than can. Only about one-quarter of the population posesses the special gene that allows them to smell the compounds in the urine. Special indeed!