Your example of someone who can smell but not produce the smell is familiar to me — up until very recently I thought this was my situation. But after dilly-dallying in the restroom after a recent asparagus-containing meal, I realized that in fact I am a producer. I just never stuck around long enough to find out! Maybe there are gradients of detection ability and production capacity — you and I might be on the low end of both.

We’re tackling the problem of the genetic basis of fascinating human traits like asparagus pee (as well as more serious traits and conditions) with the research arm of 23andMe: 23andWe. If you’re a 23andMe user, you can start helping right now by taking a few surveys!

Researching in PubMed throws up two alternative points of view:

1. There are “producers” and “non-producers” of the smell.
2. There are “smellers” and “non-smellers” of the smell.

My own limited study (sample size one) is a subject who can smell others, but not their own - suggesting to me that they are a smeller but a non-producer.

I’d have thought it most likely that there is variation in both the ability to produce and to smell. But perhaps I am wrong. If we were to look at SNPs in olfactory and metabolic genes, would we see distinct subgroups of people?