How Many Smells Can You Smell?

How Many Smells Can You Smell?

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[MUSIC] The sense of smell is probably nature’s
oldest. We can trace its odoriferous origins back to the single-celled organisms who sampled
Earth’s most primordial perfumes. Humans depend mostly on sight and sound to
navigate our world, but on every step of that journey we are led by our noses. Literally,
because it’s on the front of your face. [MUSIC] Our eyes and ears can be fooled by illusions
or noise, but not our noses. And compared to the spectrum of smell, our tastebuds are
crude, like looking at Van Gogh on an Atari. Of the human genome’s 20,000 or so genes,
almost a thousand code for olfactory receptors. Those genes have duplicated and specialized
throughout our aromatic evolution, and they’re found on all but two of your chromosomes. Being the eyeball-dependent apes that we are,
only about 400 of those olfactory receptor genes are still functional, each of them is
specific to certain chemicals. During each of the 20,000 or so breaths that
you take every day, air molecules float back and land on mucus-covered tissue the area
of a couple postage stamps, they’re packed with about 40 million special scent-detecting
nerves. These nerves are unique: They’re the only
ones in your body directly exposed to the environment, and they’re regularly replaced
about once a month. Each nerve ending is covered in just one of
your 400 or so receptor types. One group of nerves for a Christmas tree, another for cinnamon.
If an odor molecule has just the right shape, it can fit like a tiny lock and key and trigger
that nerve. But because each lock can accept many shapes of keys, we’re able detect lots
more than 400 chemical odors. Sometimes, molecules with completely different
3D shapes can trigger the same receptor, so some scientists think molecular vibrations
might determine which keys unlock which receptors. When we smell, say, a rose, we’re experiencing
a mosaic of more than 200 chemicals. We can detect some of them at concentrations as low
as two molecules in a billion. We can piece apart a smell with chemical instruments,
but that doesn’t equate to the experience of the smell. Olfactory nerve impulses enter the brain near
the amygdala and other regions that process emotion and memory. And people rate memories
evoked by smell as more emotional than those triggered by sight and sound. Our smell-associated memories tend to peak
around age 5, which is why the first whiff of a scent is our most memorable one, which
is why no matter how many old ladies I meet that wear grandma’s perfume, I always picture
her. Smell is the first sense that all of us use.
As babies, we can sniff out our parents before we ever lay eyes on them. You might have smelled your first smell even
before that. Human sperm are covered in the same type of odor detection proteins as we
find inside our noses. Scientists aren’t sure exactly what they’re “smelling”
for, but wherever that chemical quest ended, you began. The scents we encounter are molecular mixtures,
though, not individual odors. So how many different smells can we smell? Compared to our eyes and ears, our sense of
smell may be the most boundless. Taking into account the wavelengths of light we can detect
using our three types of color receptors and our eyes’ resolution, scientists think we
can distinguish between two and a half and seven and a half million colors. For sounds,
that number is just 340,000. For a long time, scientists put our scent
resolution at a measly 10,000 different smells… but it turns out no one ever really tested
that. I guess you’d say they sort of pulled it out of thin air. Sorry. That joke kind
of stunk. But this year scientists upped our smell estimate
to 1 trillion. That enough scratch and sniff stickers to reach from here and back to the
moon 32 times. Truth is, though, we don’t really know enough
about how our brain processes mixtures of odor molecules, or how many dimensions of
smell we can recognize at once, to even know if that’s a good guess. It might be lower,
or even higher. The speed of smell, riding the breeze to reach
our noses, might be slower than light or sound. But it can deliver messages from way beyond
the limits of our eyes and ears… from miles, or even years away. Is there a smell that conjures up a special
memory for you? Let me know down in the comments, and stay curious.

100 thoughts on “How Many Smells Can You Smell?”

  1. When I smell salt water I always think of Ocean City, NJ because I go there every year (except the few years I go to Disney world) for vacation

  2. I have this sponge that has the "new car/new shoe" smell, and I think i'm addicted to it. I huff that thing way to much

  3. How about an episode comparing human and canine senses of smell? Even though a huge fraction of a dog's brain is dedicated to smell, ours is so much larger that even with a much smaller fraction of our brains involved, we have many more brain cells processing smells.

  4. There has been many times a smell would conjure up memories for me. For example the other day I was eating a chicken sautee at my workplace's restaurant, the dish had a smell, a combination of spices, which was about to make me remember something but because I'm a chitty chat of a person I didn't wait for the smell to do its job in my brain, quickly I said: Déjà vu!.. and my mind went blank. No silly! It wasn't déjà vu. I was just about to remember something Ah! but that sudden reaction prevent me from remembering whatever I was about to remember. I tried the dish again but the feeling that I'm about to remember something was gone. It was kind of like you know the name of something but you just can't say it. Still it had a familiar smell. Maybe I lost then the memory of a time long forgotten. But of course, these are all what I feel and sorta induced what happened. Might be completely wrong keheh. Who knows what was happening in the universe in my brain. ^_^

  5. Lets see… The smell of cigarettes reminds me of my mom and my aunt. My phone has a smell, (its kinda earthy because it has some nasty bacteria growth on the back of it and Because I left it in my mint garden once and It still smells like mint) It reminds me of the out side. My room has a sent, its a mix of mint, chocolate, ginger ale and dust. It makes me happy.

  6. The smell of damp warmth and bird seed make me happy. It reminds me of my parakeets. It's hard to explain.

  7. I remember one day getting to see a durian fruit for the first time (if you don't know what they are, they're extremely smelly fruit that tastes amazing, there even is a bubble tea ad for durian that says "Smells like Hell, Tastes like heaven") and I got the opportunity to cut it open. I took a big breath through my nose, and I starting gagging. I quickly cut the fruit and quickly stepped back. I never wanted to see one ever again.

  8. I remember the smell of my mothers old garden as a child and sometimes the salads i make remind me of the garden because the taste is the same as the garden smell

  9. The human nose can distinguish at least 1 trillion different odours, a resolution orders of magnitude beyond the previous estimate of just 10,000 scents, researchers report today in Science1.

    Scientists who study smell have suspected a higher number for some time, but few studies have attempted to explore the limits of the human nose’s sensory capacity. “It has just been sitting there for somebody to do,” says study co-author Andreas Keller, an olfactory researcher at the Rockefeller University in New York.

    To investigate the limits of humans' sense of smell, Keller and his colleagues prepared scent mixtures with 10, 20 or 30 components selected from a collection of 128 odorous molecules. Then they asked 26 study participants to identify the mixture that smelled differently in a sample set where two of three scents were the same. When the two scents contained components that overlapped by more than about 51%, most participants struggled to discriminate between them. The authors then calculated the number of possible mixtures that overlap by less than 51% to arrive at their estimate of how many smells a human nose can detect: at least 1 trillion.

    Donald Wilson, an olfactory researcher at the New York University School of Medicine, says the findings are “thrilling.” He hopes that the new estimate will help researchers begin to unravel an enduring mystery: how the nose and brain work together to process smells.

    A human nose has around 400 types of scent receptors. When the smell of coffee wafts through a room, for example, specific receptors in the nose detect molecular components of the odour, eliciting a series of neural responses that draw one’s attention to the coffee pot. But many details of that sequence are still unknown.

    “The relationship between the number of odorants that we can discriminate and the number of receptors that we have is unclear,” says Noam Sobel, a neuroscientist at the Weizmann Institute of Science in Rehovot, Israel. Some scientists assume that having more types of scent receptors indicates a more-sensitive sniffer.

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    But that is not the only difficulty facing scientists exploring the bounds of our ability to smell.

    “It’s hard to organize odours,” Wilson says. Researchers can group scents into categories, but the relationship between those categories is not clear; unlike colours or sounds, smells do not fall along a clear continuum. In practical terms, Wilson says, that makes it challenging to objectively compare the complex, musky scent of a US drugstore cologne like Axe body spray with a rival, such as Old Spice, or with something that smells of vanilla.

    Those questions remain for future study. But the new findings may help put to rest at least one longstanding assumption, keller says. “My hope is that this helps to dispel the myth that humans have a bad sense of smell,” he says.

  10. The smell of my grandma's old house is simultaneously comforting and painful. Comforting because it reminds me of my childhood which I spent mostly in that house, and painful because now it's just a lifeless shell of its former self and all the beautiful trees and flowers have been cut down and all the old toys and books thrown away.

  11. for some reason, the certain smell of hand sanitizer reminds me of kindergarten, since we would have snack time right after nap time, and we would put on hand sanitizer

  12. I cannot smell, anyone able to describe the sense of smell to me?
    You all might think I'm kidding, but I really can't and this is a genuine question.
    Thanks

  13. Assuming evolution is true, how do we smell synthetic chemicals? Our brains have never experienced the sensory input we get from smelling chemicals that don’t normally exist in nature. Or is that why some things don’t have a smell?

  14. The smell of smoke triggers multiple memories. My grandpa was a smoker so that's one. Gasoline triggers quite a few memories as well.

  15. i wont ever forget the smell of my first girlfriend or of her family :thinking: 🙂 it hits my brain like a truck ^^ no joke it feels like a thunderstorm in my head when i smell it

  16. Cats and Vannilla are my memory smells, and I love it! Vannilla because it's soothing, and Cats because they are SO FLIPPING ADORABLE!!!!

  17. The smell of diesel fuel especially when mixed with dust from construction reminds me of my time in Afghanistan whenever I am near a large piece of equipment or a bus I have to remind myself where I am.

  18. The smell of my kindergarten and first grade school, Willis Lane Elementary, conjured up some powerful emotions when I smelled it many years after having gone there. It was powerful and strange since I used to be really apathetic and depressed during that time in my life.

  19. Hi! I'd like to know where you got the estimate of 340,000 sounds. As an acoustician it seems really low to me.

  20. Special Smell? Well…it might sound weird but a certain smell of sweat reminds me of my mum and dad…They always did hard and tiring physical jobs and sweat a lot aaannd the small little me liked to hug mum and dad reeeeally much!

  21. I do rely a lot on my nose because I really love cooking… and eating 😊 my favorite smell is cheese with browning onions, fried potatoes and Bratwurst

  22. I can smell color, good and bad people, and a bag of weed a block away. I can even smell the cycle of women.

  23. My friend says I am a "super smeller." For some reason I smell scents, even the faintest, stronger than other people. It sucks when people fart because I'm the first one to smell it, giving everyone in the room a heads up.

  24. when ever i smell my deodorant it reminds me of a christmas vacation to my great grandfathers house I'm nine lol

  25. The smell of methane reminds me of my grandparents because they live in India where the air is full of methane

  26. For me, my sound memories are more memorable. Like my trip to Colorado, I would listen to the same sound over and over, and now when ever I listen to it, I think of Colorado.

  27. Whats also interesting is that the nose of every animal is close to the mouth! Cause you got to smell what ya eatin!

  28. The smell of petrol tastes like something delicious I've never eaten before, that thing might not even exist, but why does this smell tastes so good? How can a smell taste like somthing? is it because smell and taste diverses from the same sense?

  29. I have a strong sense of smell and my family has i guess normal sneses. Cause i'll smell something like the dog food and they'd be like what?

  30. Even though this may sound a little childish and cheesy, I think the smell that triggers me the most (emotionally) is the one of the girl I've liked for like three years now

  31. My grandpa would smoke cigars and chew tobacco a lot. It annoyed me while he was alive and I always begged him to stop because the smell was so nasty, but a few months after his passing I walked by a man smoking a cigar and instantly I broke down in tears. Now I find comfort in the smell. And recently I even went to a store and talked to a man who started chewing the same brand my grandpa chewed, and as I smelled it on his breathe all I could think of was hanging out with my grandpa. No other senses trigger such strong memories of him than those two smells.

  32. Is it weird that I can't recall–or perhaps I have a difficulty to recall–memory of smells? And of taste to that matter.

  33. Yes scientist have this theory since 1950s, but it can't be the whole story. How come that benzaldehyde and cyanide smell the same but they have different atomic bonds (they dont look the same)? There is a great video about this and it concerns quantum mechanics. https://www.youtube.com/watch?v=3P7B_LkSlKQ

  34. I just came here to feel sorry for myself. Sinusitis is a wonderful thing… right guys???? Oh, and it’s even better when you have hay fever!

  35. Whenever the season is changing. I always smell the previous years previous season I never understood why. Thanks for for the insight.

  36. My favorite smell is Pine-So Because when I was little my dad use it to clean. But the werid thing is that I think of jelly beans when I smell Pine-So.

  37. Hot focaccia… it's a sort of flat bread typical of the area of Genoa, Liguria. It has very few ingredients but it is very difficult to bake properly so much so that you get bad focaccia even in Genoa.
    The good one… it has an unforgettable smell.

  38. A freshly cleaned building reminds me of the first day of school. Like freshly waxed floors, swept carpets, cleaned windows, it all just reminds me of the first day of school. It's very nostalgic.

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