I don’t know about you, but when I drive over to Wawa, I’m not just excited about the mouth-watering scent of a fresh Italian hoagie—I’m equally jazzed about the whiff of petrol that immediately fills my nostrils when I pull out the nozzle at the gas pump to refuel.
Admit it, you probably like that pungent gasoline stench, too. It’s hard to describe, but the smell is a bit sweet thanks to one of the 150 or so chemicals contained in the fuel mix. Benzene, a colorless and highly flammable liquid, gives petrol its recognizable smell, but it makes up just about 1 percent of gasoline by volume, according to the U.S. Environmental Protection Agency. Yet, our sniffers are so finely attuned to the hydrocarbon that most of us can detect its presence at just 60 parts per million of air, according to the U.S. Agency for Toxic Substances and Disease Registry. (One part per million is about equal to one drop in 40 gallons, for context).
While scientists haven’t quite cracked the case on our affinity for the smell, there are two prevailing theories: one has to do with our memories, and one has to do with our brain’s reward pathway.
If you’ve ever smelled a particular cologne and immediately thought of your father, or inhaled the scent of fresh laundry and conjured images of your old job at the laundromat, you’re already familiar with the first theory, which deals with the Proust phenomenon: a strong emotional reaction to a familiar smell. This is due to the brain’s anatomy.
The olfactory bulb, located in the front of your brain, handles the sense of smell, sending data about what you just whiffed to other parts of your brain for further processing. That scent information takes a direct line to the limbic system, which controls basic emotions. The amygdala, which controls emotions like fear and pleasure, and the hippocampus, which handles memory, are both structures of the limbic system, which have tons of neural connections near the olfactory bulb.
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As a result, that information about the smell of gasoline is quickly passed on from the olfactory bulb to the parts of your brain that control your emotions and memories. Fond memories of riding dirt bikes with your brother can trigger subconscious happy memories just by inhaling a bit of gasoline while filling up your car’s gas tank and staring off into space.
The second theory deals with the mesolimbic pathway, also known as the reward pathway. When you smell benzene or other hydrocarbons, it suppresses your nervous system, giving you a temporary euphoric feeling (yes, kind of like huffing paint, which I don’t recommend you try). When that occurs, your mesolimbic pathway doles out the neurotransmitter dopamine, making you feel happier and reinforcing that whatever you just smelled is very, very good stuff.
That said, if you relish the aroma of gasoline at the pump on a hot summer day, you’re definitely not a weirdo. Just remember that benzene is a carcinogen that’s pretty dangerous to inhale for long periods of time or at high concentrations.
So take a deep breath and smell the petrol. But maybe just one little whiff.