how many odors can humans distinguish between?

Humans can distinguish at least one trillion different odors. This updated estimate is vastly higher than the long-held belief from the 1920s that humans could only discriminate about 10,000 odors. Recent scientific research involving psychophysical testing of odor mixtures showed that the human olfactory system, with its hundreds of different olfactory receptors, far outperforms other senses in the number of distinct stimuli it can discriminate.