Smell
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Our olfactory system has an impact not only on what we smell but also on how we taste
A highly complex system, it senses nuanced ‘flavours’ and aromas, including those that the taste buds are too limited to detect.
As one of the hardest senses to find descriptive language for, it can feel uncomfortable writing any ‘definitive’ descriptions of a smell.
This is where TSM comes in.
Our noses have the potential to detect trillions of distinct smells – and it’s just as numerous when it comes to thinking about collections. With a complex sensory system comes numerous ways it can be described and understood.
Smell also interacts with other sensory systems – perhaps most notably our sense of taste and interoception.
This page encourages the development of vocabulary for describing smell, and to notice (and accept) how subjective the language we use can be in any records or interpretation.
Let’s explore our sense of smell
Watch the video and/or read the transcript below.
Transcript
It’s the first sense you use when you’re born. One out of every fifty of your genes is dedicated to it. It must be important, right? Okay, take a deep breath through your nose. It’s your sense of smell, and it’s breathtakingly powerful.
As an adult, you can distinguish about 10,000 different smells. Here’s how your nose does it.
- Smell starts when you sniff molecules from the air into your nostrils.
- 95% of your nasal cavity is used just to filter that air before it hits your lungs.
- But at the very back of your nose is a region called the olfactory epithelium, a little patch of skin that’s key to everything you smell.
- The olfactory epithelium has a layer of olfactory receptor cells, special neurons that sense smells, like the taste buds of your nose.
- When odour molecules hit the back of your nose, the olfactory epithelium they get stuck in a layer of mucus covering the olfactory epithelium.
- As they dissolve, they bind to the olfactory receptor cells, which fire and send signals through the olfactory tract up to your brain.
As a side note, you can tell a lot about how good an animal’s sense of smell is by the size of its olfactory epithelium. A dog’s olfactory epithelium is 20 times bigger than your puny human one.
But there’s still a lot we don’t know about this little patch of cells, too. For example, our olfactory epithelium is pigmented, and scientists don’t really know why.
But how do you actually tell the difference between smells?
It turns out that your brain has 40 million different olfactory receptor neurons.
So odour A might trigger neurons 3, 427, and 988, and odour B might trigger neurons 8, 76, and 2,496,678. All of these different combinations let you detect a staggeringly broad array of smells.
Plus your olfactory neurons are always fresh and ready for action. They’re the only neuron in the body that gets replaced regularly, every 4-8 weeks.
The olfactory tract
Once they are triggered, the signal travels through a bundle called the olfactory tract to destinations all over your brain, making stops in the amygdala, the thalamus, and the neocortex. This is different from how sight and sound are processed. Each of those signals goes first to a relay centre in the middle of the cerebral hemisphere and then out to other regions of the brain.
But smell, because it evolved before most of your other senses, takes a direct route to these different regions of the brain, where it can trigger your fight-or-flight response, help you recall memories, or make your mouth water.
But even though we’ve all got the same physiological set-up, two nostrils and millions of olfactory neurons, not everybody smells the same things.
Different scents
One of the most famous examples of this is the ability to smell so-called ‘asparagus pee’. For about a quarter of the population, urinating after eating asparagus means smelling a distinct odour. The other 75% of us don’t notice. And this isn’t the only case of smells differing from nose to nose.
For some people, the chemical androstenone smells like vanilla; to others, it smells like sweaty urine, which is unfortunate because androstenone is commonly found in tasty things like pork. So with the sweaty urine smellers in mind, pork producers will castrate male pigs to stop them from making androstenone.
The inability to smell
The inability to smell a scent is called anosmia, and there are about 100 known examples. People with allicin anosmia can’t smell garlic. Those with eugenol anosmia can’t smell cloves. And some people can’t smell anything at all.
This kind of full anosmia could have several causes. Some people are born without a sense of smell. Others lose it after an accident or during an illness. If the olfactory epithelium gets swollen or infected, it can hamper your sense of smell, something you might have experienced when you were sick.
The ability to taste
Not being able to smell anything can mess with your other senses, too. Many people who can’t smell at all also can’t really taste the same way the rest of us do. It turns out that how something tastes is closely related to how it smells.
As you chew your food, air is pushed up your nasal passage, carrying with it the smell of your food. Those scents hit your olfactory epithelium and tell your brain a lot about what you’re eating. Without the ability to smell, you lose the ability to taste anything more complicated than the five tastes your taste buds can detect: sweet, salty, bitter, sour, and savoury.
So, the next time you smell exhaust fumes, salty sea air, or roast chicken, you’ll know exactly how you’ve done it and, perhaps, be a little more thankful that you can.
There are many smell charts out there that can cover a vast array of contexts.
For heritage settings, check out the brilliant scent wheel developed by Odeuropa to find some vocabulary.
You can also make use of the terminology for ‘taste’, which often relies heavily on smell.
Watch (or read the transcript for) this brilliant video by Alexandra Horowitz to get your olfactory system working.
Test out her techniques on some things you have in front of you (even if they don’t obviously have a scent).
- Items on your desk
- Your coat
- Your drink
- Office tech (desktop, laptop, printer)
NB please do not ‘smell’ any hazardous items, where the properties could cause physical harm.
Transcript
Perfumers can learn to distinguish individual odours in a fragrance made of hundreds of scents. Tea experts have been known to sniff out not just the location where a tea was from, but the season of harvest and whether it was planted by a plum tree. And the New York City Transit Authority once had an employee responsible only for sniffing out gas leaks in the subway system.
Can just anyone learn to smell with the sensitivity of those experts?
For most of us, what we smell is largely involuntary, whether it’s garbage behind a restaurant, the shampoo of the woman leaving an elevator as you enter, or a bakery’s fresh-made bread.
With a few million olfactory receptors in our noses, we clearly don’t lack the ability to smell well. We just might not always pay close enough attention. That’s a shame because we may be missing opportunities to make strong emotional connections.
Smells are powerfully linked to emotions and can awaken memories of places we’ve long ago left and people we’ve loved.
But fortunately, it is possible to train our brains to smell better. For example, Helen Keller was able to recognise a person’s work, and in her words, distinguish the carpenter from the iron worker, the artist from the mason or the chemist, by a simple inhale.
Follow these steps and you too can change the way the world smells to you.
1. First, stick your nose in it
- Some animals that are known to be great smellers, like dogs who can sniff out explosives and pigs who can find truffles underground, put their noses right at the place they want to smell.
- Human noses, meanwhile, are casting around in the middle of the air, giving us an anatomical disadvantage.
- So bring your nose close to the world around you. The ground, surfaces, objects, the food in your hand. Get close to your dog, your partner, the book you’re reading.
- Not only will your nose be closer to the odour source, but the warmth of your breath will make odours easier to smell.
2. Second, sniff like you mean it
- Smelling actually happens way up near the bridge of our noses in a postage stamp-sized square of tissue called the olfactory epithelium.
- When we sniff, odour molecules are sucked up into our nostrils until they hit this tissue where they combine to our olfactory, or scent, receptors.
- When we inhale normally, only a little air makes it there. But one or two solid sharp sniffs will ensure that more air gets to your smell receptors.
- After just a few more sniffs, the receptors, which are best at noticing new smells, turn off temporarily. So you can give your nose a rest and sniff again later.
3. Finally, dwell on the smell
- Most smells pass by us with little attention, but simply noticing what you’re smelling and by trying to describe it, name it, and locate its source, you can expand your vocabulary of smells.
- When an odour molecule binds to a scent receptor, it sends an electrical signal from the sensory neurons to our brain’s olfactory bulbs.
- The signal then continues to other areas of the brain, where it’s integrated with taste, memory, or emotional information before registering to us as a smell.
- FMRI research shows that the extra time spent focusing on scent changes the brain of experienced smellers. For them, perceiving and imagining odours becomes more automatic than for non-experts.
To get started yourself, take ingredients from your kitchen:
- Spices, vanilla, or fruit, but never anything toxic.
- Close your eyes and bring them under your nose.
- Sniff and try to name the source.
- Over time, you’ll begin to appreciate nuances in familiar odours and recognise characteristics of new and unusual smells.
The perfumer has practised these steps enough to become an artist of odour, but even if you never pursue smelling to that degree, the spectacular result of an unspectacular action will change how you sense and experience your days.
No source that relates heritage organisations to smell can serve you better than the incredible work done by Odeuropa.
To support olfactory readings of your collections, check out Odeuropa’s impressive Smell Recorder website: https://explorer.odeuropa.eu/
That said, remember that you, your collections and your interactions are unique, so give time to make give your own olfactory assessments and readings.