Humans can probably distinguish at least many billions of different odors, and one influential (but debated) study estimated a lower bound of about 1 trillion distinct smells.

Why you’ve heard “1 trillion smells”

  • For decades, textbooks repeated that humans can tell about 10,000 odors apart, but that number was more of a guess than a measured value.
  • In 2014, researchers at Rockefeller University tested people with mixtures of odor molecules and calculated that the average person can discriminate at least one trillion different odor combinations.
  • They used mixtures built from 128 base odor molecules, then used how often people confused two mixtures to estimate how many combinations should be distinguishable overall.

In other words, “1 trillion” is a conservative lower bound from that experiment, not a precise final count.

The scientific debate

  • Soon after, other scientists argued that the math and assumptions in that trillion estimate were fragile—tweaking them could give wildly different numbers.
  • A 2015 critique showed that the same framework could generate estimates ranging from very low to absurdly high, so it concluded that “more than one trillion odors” is not firmly proven.
  • Because of this, the true number of discriminable odors is still scientifically uncertain , though nearly everyone agrees it’s far higher than 10,000.

What we can say with confidence

  • Humans have hundreds of different olfactory receptors (around 400+), which already hints that our smell space is extremely rich.
  • Experiments show that people can reliably tell apart very large numbers of odor mixtures, especially when the mixtures don’t overlap too much in their components.
  • The best current evidence says our nose is capable of distinguishing far more odors than our eyes can colors , likely in the billions to trillions range, but we don’t yet have a universally accepted exact figure.

Quick Scoop (TL;DR)

  • Old claim: about 10,000 odors (not really measured).
  • Modern claim: at least 1 trillion odors , from a 2014 study.
  • Current view: the exact number is unknown , the “trillion” figure is debated, but humans clearly distinguish an enormous number of smells, vastly more than previously thought.

Information gathered from public forums or data available on the internet and portrayed here.