There are lots of reasons why somepeople have more acute senses of smell than others. For me it is "self defense" for lack of a better term. I have become more aware of all odors around me over the last few years for several reasons.
First, I have pretty severe allergies and didn't realize how deficient my sense of smell had become with the constant congestion. When the congestion was cleared with agressive allergy treatment, I could smell much more.
Second, when my sinuses cleared so that I could smell things again, I realized that just about every odor triggered my asthma. I have to be very aware of the odors around me in order to treat my asthma or leave a situation to avoid an attack. People who have odor triggered migraines are the same way. For us it is a learned defense mechanism.
I hope other chime in with other thoughts and explanations.
Hi, welcome to the forum, smell constitutes as one of the special senses in humans. It plays many role from identifying the substance (acceptable and toxic), as defense mechanism etc. The main component of smell system is receptors known as olfactory chemoreceptor cells, which are primary neurons that project directly to the brain. There will continuous formation of new receptors esp. in adulthood. They turnover reduces in advancing age.
The receptor formation and sensitivity varies from person to person. Hence, there can be difference in intensity of smell across the population. The main factor for such difference can be injury from infection, inflammation, and noxious chemical agents which causes early death of these receptors and also prevents formation of new receptors. In such cases, the intensity or ability to smell reduces over a time. I hope this information helps. Take care and regards.