<ul>
<li>Odour molecules that move through the air up your nostrils will bind to special smell receptors on the surface of nerve cells. </li>
<li>The nerve cells send a signal to the brain's olfactory bulb, that is behind the bridge of the nose.</li>
<li>People have about 400 different smell receptor types. </li>
<li>The odour molecules create a pattern of activation in the nerve cells that the brain translates as a smell.</li>
</ul>

How smell works

<ul>
<li>Smells can alert us about danger - we're repulsed by the smell of sewage and rotting food.</li>
<li>We don't all respond to odour molecules in the same way. </li>
<li>Butyric acid contributes to the smell of both Parmesan cheese and vomit, so it may smell offputting or appealing, depending on the situation.</li>
</ul>

How we react to certain smells

<p><strong>A complete loss of smell, known as anosmia, can occur after a cold, sinus infection or even a bump to the head.</strong></p>
<p><strong>Anosmia affects the flavour of food.</strong> However, it isn't always permanent and may recover naturally or through exercises like 'smell training' to re-stimulate the olfactory system.</p>

When we lose our sense of smell

<h2>How does smell work?</h2><p>If you’ve ever stopped to smell the roses, a cocktail of hundreds of different odour molecules will have wafted through the air and up your nostrils. At the top of your nose, the molecules bind to special smell receptors on the surface of nerve cells, which send a signal to the brain’s olfactory bulb, located just behind the bridge of the nose. Humans have around 400 different smell receptor types, and one odour molecule may bind to many of them. Together, the odour molecules create a pattern of activation in the nerve cells that our brain interprets as ‘a smell’.</p><h2>Why do we like certain smells but not others?</h2><p>Smells can warn us about danger – we’re repelled by the smell of sewage and rotting food, for example. But according to smell expert Dr Andreas Keller from Rockefeller University, it’s difficult to tell whether we’re born with these preferences or whether they’re learned. Context plays a big role. Butyric acid is a chemical that contributes to the smell of both Parmesan cheese and vomit, so it may smell repulsive or appetising, depending on the situation. The answer is also partly down to our DNA – the genes that code for our smell receptors can vary between people, so we don’t all respond to odour molecules in the same way.</p><picture><source media="(max-width: 320px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=300%2C199, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=45&amp;resize=600%2C399 2x, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=45&amp;resize=796%2C530 3x" type="image/webp" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=300%2C199, 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https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=45&amp;resize=600%2C399 2x, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=45&amp;resize=796%2C530 3x"><source media="(max-width: 375px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=355%2C236, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=45&amp;resize=710%2C472 2x" type="image/webp" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=355%2C236, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=45&amp;resize=710%2C472 2x"><source media="(max-width: 375px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=355%2C236, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=45&amp;resize=710%2C472 2x" type="image/jpeg" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=355%2C236, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=45&amp;resize=710%2C472 2x"><source media="(max-width: 425px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=405%2C269, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=45&amp;resize=796%2C530 2x" type="image/webp" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=405%2C269, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=45&amp;resize=796%2C530 2x"><source media="(max-width: 425px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=405%2C269, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=45&amp;resize=796%2C530 2x" type="image/jpeg" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=405%2C269, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=45&amp;resize=796%2C530 2x"><source media="(max-width: 589px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=554%2C369" type="image/webp" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=554%2C369"><source media="(max-width: 589px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=554%2C369" type="image/jpeg" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=554%2C369"><source media="(min-width: 992px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=620%2C413" type="image/webp" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=620%2C413"><source media="(min-width: 992px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=620%2C413" type="image/jpeg" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=620%2C413"><source media="(min-width: 768px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=408%2C271, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=45&amp;resize=796%2C530 2x" type="image/webp" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=408%2C271, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=45&amp;resize=796%2C530 2x"><source media="(min-width: 768px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=408%2C271, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=45&amp;resize=796%2C530 2x" type="image/jpeg" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=408%2C271, https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=45&amp;resize=796%2C530 2x"><source media="(min-width: 590px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=556%2C370" type="image/webp" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?webp=true&amp;quality=90&amp;resize=556%2C370"><source media="(min-width: 590px)" data-srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=556%2C370" type="image/jpeg" srcset="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=556%2C370"><img width="620" height="413" alt="We're guessing this sewer will not smell like roses. © Getty" title="What's in a smell? © Getty" src="https://images.immediate.co.uk/production/volatile/sites/4/2019/01/GettyImages-890873886-crop-b2be960.jpg?quality=90&amp;resize=620%2C413"></picture><div class="caption" dir="ltr"><figcaption class="caption" dir="ltr"><span class="caption" dir="ltr"> We’re guessing this sewer will not smell like roses. © Getty</span></figcaption>
</div><h2>What happens when we lose our sense of smell?</h2><p>We all have at least one genetic ‘blind spot’ in our sense of smell, which means we simply can’t detect certain odour molecules. One famous example is how only some people notice a strong odour in their pee after eating asparagus. Anosmia – a complete loss of smell – can occur after a cold, sinus infection or even a bump to the head. Anosmia impacts the flavour of food, but goes far beyond that – one anosmiac has described it as like “living behind a pane of glass”. Luckily, anosmia isn’t always permanent, and may recover naturally or through exercises like ‘smell training’, which uses distinctive smells such as essential oils to re-stimulate the olfactory system.</p><p dir="ltr"><strong dir="ltr">Anand Jagatia</strong> is the presenter of Do You Smell What I Smell?– an episode of <em dir="ltr">CrowdScience</em> that can be streamed at&nbsp;<a href="http://www.bbc.co.uk/programmes/w3cswvxk" dir="ltr">http://www.bbc.co.uk/programmes/w3cswvxk</a></p><p><strong>Read more:</strong></p>

We teamed up with the folks behind BBC World Service’s CrowdScience to answer your questions on one topic - this week it's all about smell.

personaldevelopment

Personal Development

health

Health

communication

Communication

scienceandnature

Science & Nature

<p>If you’ve ever stopped to smell the roses, a cocktail of hundreds of different odour molecules will have wafted through the air and up your nostrils. At the top of your nose, the molecules bind to special smell receptors on the surface of nerve cells, which send a signal to the brain’s olfactory bulb, located just behind the bridge of the nose. Humans have around 400 different smell receptor types, and one odour molecule may bind to many of them. Together, the odour molecules create a pattern of activation in the nerve cells that our brain interprets as ‘a smell’. </p>

Why do we like certain smells but not others?

<p>Smells can warn us about danger – we’re repelled by the smell of sewage and rotting food, for example. But according to smell expert Dr Andreas Keller from Rockefeller University, it’s difficult to tell whether we’re born with these preferences or whether they’re learned. Context plays a big role. Butyric acid is a chemical that contributes to the smell of both Parmesan cheese and vomit, so it may smell repulsive or appetising, depending on the situation. The answer is also partly down to our DNA – the genes that code for our smell receptors can vary between people, so we don’t all respond to odour molecules in the same way. </p>

What happens when we lose our sense of smell?

<p>We all have at least one genetic ‘blind spot’ in our sense of smell, which means we simply can’t detect certain odour molecules. One famous example is how only some people notice a strong odour in their pee after eating asparagus. Anosmia – a complete loss of smell – can occur after a cold, sinus infection or even a bump to the head. Anosmia impacts the flavour of food, but goes far beyond that – one anosmiac has described it as like “living behind a pane of glass”. Luckily, anosmia isn’t always permanent, and may recover naturally or through exercises like ‘smell training’, which uses distinctive smells such as essential oils to re-stimulate the olfactory system. </p>

What’s in a smell?

How smell works

How we react to certain smells

When we lose our sense of smell

Lauren W.'s ideas are part of this journey:

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