What’s That Smell?

If you ranked the animal kingdom’s master smellers, humans would be about as proficient as mice.

I was born with a weak sense of smell. No medical authority has ever confirmed this, but I’m sure it’s true.

Somehow, I’m only able to sniff out the most pungent odors drifting about. This means I can easily pick out the sweet and tangy smell of kal-bi from my favorite Korean take-out restaurant the moment I enter their parking lot. It also means I can detect anything within a one-mile radius being cooked with garlic. Neither of these is at all bad.

Unless I compare myself to my girlfriend, Dawn, who possesses the most acute sense of smell I’ve yet encountered.

Dawn can smell the faint differences between cookies baking with milk chocolate morsels and dark chocolate morsels. And on a recent nighttime stroll along a Honolulu pier, Dawn’s nose easily picked out the ingredients of competing menu specials at two nearby restaurants, while mine was left deconstructing the paralyzing odor drifting our way from a wastewater treatment facility across the harbor. Unfair? You bet. But unnatural? Hardly.

Odors are composed of lighter-than-air molecules that originate from just about anything: food, flowers, especially waste. Everything we smell comes from something that released these molecules, which means each molecule is actually a tiny piece of whatever matter it came from. Spooky, when I think of what I might have been inhaling at the pier. But I digress.

Almost all creatures outside of the plant world have an ability to sense these molecules. Even if they lack a nose. Insects have chemical receptors on their antennae, legs or feet. Salmon and trout locate their original spawning areas by smell. For many animals, smell is even a primary means of communication.

The collective structure that allows us to sense and process odors is called the olfactory system. Behind our noses, at the top of the nasal passage, a thousand or so sensory nerve cells called neurons are open to the air we breathe. Each neuron in this postage-stamp sized patch is equipped with a hair-like projection called a cilium, which binds to passing odor molecules. When binding occurs, neurons send electrical signals to the olfactory bulb, located just above them, in the lower brain. Patterns in the signals are interpreted by our brain as pleasant or offending odors, and then identified.

Though humans can distinguish between thousands of odors, the number of odor receptor neurons we have is quite low compared to the rest of the animal kingdom. Our 5 million or so receptors put us on par with mice. A bloodhound has about 100 million. This doesn’t mean that human receptors are any less sensitive than other animals. Only that we don’t have their range.

And like height and weight, all human olfactory systems are not created equal. Take Dawn and me, for example.

Human olfactory neurons — each encoded by a specific gene — bond with passing odor molecules. Dawn’s impressive sense of smell could be the result of an especially acute collection of neurons. On the other hand, the limited power of my olfactory system may result from damaged genes (or missing ones), preventing me from detecting certain odors.

It’s also likely that Dawn unintentionally developed a more well-trained or exercised olfactory system than mine. Food critics and wine tasters must train their noses to distinguish between a wide array of aromas and tastes. Dawn is neither (at least not professionally), but she is able to smell and taste even the faintest presence of dozens of ingredients, such as cilantro, which she hates. Which brings up another sad fact: Because our sense of taste and smell are directly related, my inferior sense of smell also hampers my ability to really taste certain foods.

But I’m OK with that. I’ll have to be. After all, there’s no simple cure for my olfactory ailment, which may be related to missing gene factors, a deviated septum, a past viral infection, inhalation of toxic chemicals or a handful of other things. And fortunately, a decreased sense of smell is hardly fatal and, in my experience, not terribly annoying.

Besides, if you’re buying, I’m definitely your man for sniffing out the best Korean cuisine in Honolulu.

Published: Island Scene Online, November 8, 2000

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