Can the Internet Smell?
Why bother digitizing smell?
Smell is the first sense to develop in humans, and it shaped how our species chose food and related to one another. It is a chemical sense: the nose detects molecules floating in the air, and the brain blends that signal with what we see, hear and taste.
It is also deeply emotional. One whiff can bring back a grandmother’s kitchen or a summer you thought you had forgotten. By some estimates, around 75% of the emotions we feel each day are influenced by smell, often without us noticing.
And there is a market waiting. The perfume industry alone is already huge, and many people say they would enjoy smelling the scenes they watch in movies. Some companies are already thinking about selling scent data the way they sell music or video.
How does a machine smell?
Digital scent technology does two separate jobs: recognizing a smell, and recreating one.
Recognition is the work of an electronic nose, or “e-nose.” Instead of the receptors in our noses, it uses an array of chemical sensors, each sensitive to particular molecules. When a smell reaches the array, every sensor reacts a little differently, and together they produce a pattern, a kind of fingerprint. Machine learning then compares that fingerprint with a library of known smells and picks the closest match.
E-noses already do useful work. Small consumer devices can check whether whether meat or fish is still fresh. Industrial systems judge the ripeness of fruit, the quality of coffee and chocolate, or the presence of dangerous gases. In medicine, researchers use them to analyze breath for signs of asthma and other conditions.
They are far from perfect, though. Sensors drift over time, react to humidity and temperature, and struggle with new or unusual odors. There is also no agreed standard for describing smells, the way RGB describes colors on a screen.
How does a machine make a smell?
Recreating a smell is the harder job, and there are two very different ways to attempt it.
Releasing real molecules. The older approach is chemical. A device holds cartridges of scented liquid and releases tiny amounts into the air at the right moment, by heating, blowing or spraying. The idea goes back a long way: Smell-O-Vision tried it in cinemas in 1960, and the Sensorama booth in 1962. In 1999 a company called DigiScents announced iSmell, a computer gadget meant to mix thousands of everyday smells from a cartridge of 128 basic ones. Many later devices followed the same idea.
Today’s devices are much smaller, connect over Bluetooth or Wi-Fi, and can switch scents in milliseconds. The core problems remain, however. Cartridges are expensive and run out, the palette of smells is limited, and scents linger in the room long after the scene has changed.
Skipping the molecules. The newer and stranger approach uses tiny electrical currents to stimulate the nerves directly. Some researchers have stimulated the olfactory bulb, the first stop for smell signals in the brain, and produced sensations people described as sweet, chemical or fragrant. The results have been hard to reproduce reliably, and some settings caused pain or flashes of light.
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A more promising route goes through the trigeminal nerve, which gives scents like mint their cool, fresh edge. Brooks and colleagues built a small device, worn like a nose ring, that stimulates this nerve electrically. Rather than producing a particular scent, it lets people sense how strong a smell is and which side it comes from: a kind of “stereo smell.”
Where digital scent is already showing up
Even with these limits, scent technology is quietly finding its way into everyday life.
- Notifications. Small wearables can release a puff of scent when a message arrives: “scentifications” instead of beeps.
- Mood and focus. Scent devices can adjust what they release based on body signals or context, and can affect mood even at levels you barely notice.
- Cars. Certain smells are linked to higher alertness, so scent-based alerts could help keep drowsy drivers awake.
- Shops. Scent displays in shop windows, cinemas and theme parks let customers smell a product, or even design their own fragrance.
- Museums. Augmented-reality tours can release matching scents as visitors explore archaeological sites.
- Virtual reality. Adding smell to VR makes people feel more present in the virtual world, and is being explored for therapy and stress relief.
Smell, 6G and the Metaverse
This is where things get ambitious. Ericsson coined the term Internet of Senses for a future in which digital experiences engage all five senses and feel almost indistinguishable from reality. 6G, the next generation of mobile networks expected around 2030, counts the Internet of Senses among its main use cases.
The reason is speed. Sending sight, sound, touch and smell together, perfectly in sync, needs huge data rates and delays below one millisecond. 6G aims for speeds measured in terabits per second, far beyond today’s 5G.
Combine that with the Metaverse, the shared virtual spaces where we meet, work and play, and some intriguing possibilities appear:
- A doctor who receives smell data from a patient’s breath as an extra diagnostic clue, without being in the same room.
- A virtual museum visit where you smell the food and perfumes of another century.
- Games in which places and characters each have their own scent.
- Shopping online for perfume, coffee or food, and smelling it before you buy.
One day, even our digital twins, the virtual copies of ourselves and our surroundings, might come with a smell of their own.
So why can’t I smell my screen yet?
Because smell is far harder to digitize than light or sound.
A color on your screen is just three numbers: red, green and blue. A sound is a wave that can be recorded and replayed precisely. Smell is chemistry. It involves thousands of different molecules, and there is no simple set of “primary smells” that can be mixed to make all the others. Today’s devices work from a limited palette, so they can only reproduce a limited range.
Our own noses make things even trickier. Mixed smells don’t simply add up: some cancel each other out, while others blend into something entirely new. Most people can’t pick out more than three or four smells in a mixture, however complex it is. Sensitivity varies a lot from person to person, and we quickly stop noticing a smell we’ve been exposed to for a while.
In our paper we called the missing piece olfactory holography: capturing a smell in one place and recreating it faithfully in another. With today’s technology, that simply isn’t possible yet.
The last sense to go online
Smell may be the last of our senses to reach the internet, but the research is moving fast. Electronic noses and scent displays are getting smaller, cheaper and smarter every year. If we want a digital world that truly feels like the real one, sooner or later it will have to smell like it too.
This article is based on the paper “Digital Scent Technology: Toward the Internet of Senses and the Metaverse” by D. Panagiotakopoulos, G. Marentakis, R. Metzitakos, I. Deliyannis and F. Dedes, published in IEEE IT Professional, vol. 24, no. 3, 2022. Read the full paper.
