Have you ever said to a friend "That rose's smell is really sweet!", only to find that your friend can't smell anything at all?

According to a study published in the journal PNAS in May, people have different abilities to recognize certain odors (气味) — and it's linked to different genes.

For the study, 300 people were placed among 150 jars with different odors. At a given time, they had to smell an odor and then rate the intensity (强度) and pleasantness of the odor on a scale from 1 (extremely weak/unpleasant) to 7 (extremely strong/pleasant). Before they left, the participants needed to leave a blood sample.

After comparing genes of the participants, researchers found all had different smelling abilities and that the differences between these abilities could be traced to certain genes.

According to The New York Times, human beings have nearly 400 genes that directly control receptors (器官) and influence the way these receptors become active.

"Odors ... turn on specific receptors, which then tells us if we're smelling a flower, how strong we find it, and whether we like it," said Casey Trimmer, a geneticist and the lead author of the study. "One small change in the gene for the receptor can change its shape and how well the odor fits, thereby changing the awareness of the odor."

Though genes play a decisive role in our ability to smell, other factors, including attention, past associations and expectations, are important as well. For example, if we love the smell of roses, we are drawn to their smell and pay special attention to it.

But what does our different abilities to sense odors mean?

"Smelling is the most important sense for the rest of the animal kingdom," said Trimmer. Although, unlike other animals, humans aren't any longer dependent on their sense of smell to find food or detect danger, smell is still a significant sense. There is also evidence that a reduced sense of smell is an early symptom of Alzheimer's disease.