Hundreds of odour receptor types, the direct road from nose to emotion and memory, five basic tastes, the debunked tongue map — and why flavour is mostly smell.
Senses & Perception
Beginner
Smell and Taste
The Editors
September 17, 2026
3 min read
In plain English
Smell and taste are chemical senses. Your nose has hundreds of kinds of smell receptors that together can tell apart a huge number of odours. Your tongue detects five basic tastes. Most of what we call 'flavour' actually comes from smell, which is why food tastes bland when you have a cold.
Beginner level: No background needed. Everyday language, everyday examples — the place to start.
Concepts to know first
Go deeper next
Smell: the ancient sense
High in each nasal cavity is a small patch of tissue containing millions of olfactory sensory neurons. Each neuron carries one type of odorant receptor. In 1991 Linda Buck and Richard Axel discovered the huge gene family encoding these receptors — the largest gene family in the mammalian genome — earning the 2004 Nobel Prize. Humans have about 400 functional types (mice about 1,000; many human receptor genes are inactive). Each odour activates a combination of receptor types, so a limited set of receptors can distinguish an enormous range of smells.
Olfactory neurons are unusual: they're exposed to the outside world and are continually replaced throughout life. Their axons pass through small holes in the skull to the olfactory bulb. Uniquely, smell signals reach the cortex without first relaying through the thalamus, connecting quickly to the piriform cortex, the amygdala and regions near the hippocampus — one reason smells can trigger vivid emotional memories.
Loss of smell (anosmia) became widely known during the COVID-19 pandemic. It can also be an early sign of Parkinson's and Alzheimer's diseases.
Taste
The tongue's taste buds — several thousand of them, mostly in the visible bumps called papillae — contain receptor cells for five basic tastes: sweet, sour, salty, bitter and umami (savoury). Umami was identified by the Japanese chemist Kikunae Ikeda in 1908, who traced the taste of kombu broth to glutamate. Researchers continue to study candidates such as a taste for fat.
The famous tongue map, showing sweet at the tip and bitter at the back, is a myth — it came from a misreading of a 1901 German paper. All taste qualities can be detected across all regions of the tongue that have taste buds.
Flavour is mostly smell
When you chew, aromas travel from the back of the mouth up into the nose (retronasal smell). The brain combines this with taste, texture, temperature and even sound into flavour. Hold your nose and a jelly bean's fruit flavour disappears, leaving only sweetness.
Everyday examples & things to try
Try it
The jelly bean test
Pinch your nose shut and eat a flavoured jelly bean or sweet. You'll taste sweetness, maybe sourness — but not 'cherry' or 'lemon'. Let go of your nose mid-chew and the flavour floods in. Flavour is mostly smell.
Key takeaways
- Humans have about 400 odorant receptor types; odours are coded by receptor combinations.
- Smell reaches emotion and memory areas without a thalamic relay.
- Taste has five basics (sweet, sour, salty, bitter, umami); the tongue map is a myth; flavour is mostly smell.
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