0
Shares
0
0
0
0

Summary

Smell is the only sense with a direct pathway to the brain's emotional and memory centers. This guide breaks down the science behind smell-triggered memories, why olfactory loss can serve as an early warning sign for conditions like Parkinson's, and how olfactory training can help protect cognitive health.

Close your eyes and picture your grandmother’s kitchen. Chances are, before you see anything, you smell something. A specific dish, a particular soap, the exact scent of a room you haven’t been in for decades. It arrives before the memory does, clear and complete, as if no time has passed at all.

This is not sentiment. It is neuroscience. And what it reveals about your sense of smell is far stranger, and far more significant, than most people realize.

The Only Sense With a Direct Line to Your Brain

Every other sense you have takes the scenic route to your brain. Visual information from your eyes, sound from your ears, touch from your skin, all of it travels through a relay station called the thalamus before reaching the regions of the brain that process it. Smell is the exception.

When you inhale an odour, molecules enter your nose and bind to olfactory receptors. Those receptors generate a signal that travels directly to the olfactory bulb, a structure sitting just above your nasal cavity, which then routes immediately to the amygdala and hippocampus the brain’s centres for emotion and memory. No thalamus. No intermediary. The most primitive parts of your brain receive the signal first, before your conscious mind has had time to catch up.

This is why a smell can make you feel something before you understand what you’re remembering. The emotional response arrives first. The memory follows.

Researchers at the University of Toronto published findings in Nature Communications demonstrating that information about space and time integrates within the anterior olfactory nucleus, a region of the brain central to smell, to form what they call “what-when-where” memories. The study helps explain why smell-triggered memories are so precise and so emotionally loaded: they are encoded with a completeness that visual or auditory memories rarely match.

Why Some People Are Overwhelmed by Smell

Not everyone experiences smell the same way. For a meaningful portion of the population, certain odours are not merely unpleasant, they are physically debilitating.

This condition is called hyperosmia: a heightened and hypersensitive sense of smell that can turn a perfumed colleague, a cleaning product, or even a particular food into a source of genuine distress. People with hyperosmia may experience nausea, headaches, and anxiety from odour exposures that others barely notice.

Hyperosmia tends not to be a condition in itself but a symptom of something else. It is associated with a number of underlying conditions, including migraines, Lyme disease, and pregnancy. It has also been widely reported following COVID-19 infection, as part of a broader pattern of post-viral olfactory dysfunction. Some people report persistent smell changes, including heightened reactivity to certain odours, long after the infection itself has resolved.

What makes hyperosmia particularly complex is that research has found that people who self-report extreme smell sensitivity do not always demonstrate objectively higher detection thresholds in laboratory testing. The experience of being overwhelmed by a smell may be less about sensitivity and more about reactivity, a heightened neurological and emotional response to an odour signal, rather than a physically stronger signal itself. The brain’s interpretation of the smell, in other words, may matter as much as the smell.

This distinction is important because it points toward the broader truth about olfaction: smell is never just smell. It is always emotional, always contextual, and always filtered through the accumulated experience of the brain that receives it.

When Sense of Smell Can be Protective

Pregnancy can dramatically change the way smells are experienced. Around two thirds of pregnant women report heightened smell sensitivity, particularly during the first trimester, when previously ordinary scents such as coffee, meat, garlic or perfume can suddenly trigger nausea or disgust.

Hormonal changes, including rising levels of estrogen and hCG, are often thought to play a role. However, research suggests pregnant women may not necessarily have a physically sharper sense of smell. Instead, the brain appears to interpret certain odours as more intense and unpleasant.

Researchers believe this may have an evolutionary purpose. During early pregnancy, when a developing fetus is particularly vulnerable, stronger aversions to smells associated with potentially harmful foods or substances, such as spoiled meat, cigarette smoke and certain bitter foods may help reduce exposure to toxins and pathogens.

For most women, this sensitivity is strongest during the first trimester and gradually improves. But in severe cases, smell-triggered nausea can contribute to hyperemesis gravidarum, a serious form of pregnancy sickness.

In pregnancy, changes to our sense of smell may serve a protective purpose. In other cases, however, changes in the way we perceive odours can be an early warning sign that something else is happening in the body.

What Your Nose Knows About Your Brain Health

Here is where the science becomes particularly compelling for Canadians to understand.

Smell loss is not just an inconvenience. It is one of the earliest detectable warning signs of neurological decline. According to McGill University’s Office for Science and Society, research has found that around 90% of people with Parkinson’s disease have trouble detecting smell and this deficit can appear years before the classic motor symptoms of tremor and rigidity that most people associate with the disease.

The biology behind this connection is well understood. The abnormal proteins associated with both Parkinson’s and Alzheimer’s disease accumulate first in the olfactory bulb, before spreading to other regions of the brain. A 2025 review in Frontiers in Neuroscience confirmed that olfactory dysfunction has now been observed across a wide range of neurodegenerative conditions, including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and ALS.

A 2024 review found that olfactory loss is associated with at least 139 medical conditions, many of them linked to systemic inflammation. The researchers argue that losing your sense of smell is more than a symptom,  it may be a causal factor in declining health, given the olfactory system’s unique direct access to the brain’s memory and emotional centres.

This is why smell tests are now being explored as a low-cost, non-invasive screening tool for neurological risk. For anyone who has noticed a gradual, unexplained reduction in their ability to detect or identify odours, it is worth raising with a physician.

Can You Train Your Nose to Be Sharper?

The answer, increasingly, appears to be yes.

Olfactory training, the practice of regularly and deliberately smelling a set of distinct odours to stimulate the olfactory system, has accumulated a meaningful evidence base. Research summarized in Chemistry and Industry found that olfactory training can improve cognitive performance, with one major study reporting measurable improvements in memory and cognition in adults aged 60 to 85 who inhaled specific fragrances nightly. MRI scans in separate research confirmed that intensive olfactory training actually changes the physical structure of the brain, strengthening functional connectivity between regions responsible for smell and those responsible for higher-order thinking.

The implication is striking: your nose is not a fixed instrument. It is a trainable one, with a direct channel to the parts of your brain most vulnerable to aging and disease. Exercising it deliberately may have protective effects that extend well beyond your ability to appreciate a good meal.

What Losing Your Sense of Smell Actually Costs

COVID-19 brought anosmia into mainstream awareness in a way nothing before it had. Millions of people lost their sense of smell during infection, and for a significant portion, it did not fully return. This created an unusual natural experiment in what smell actually does for human wellbeing.

The findings have been sobering. A 2025 review published in Chemical Senses found that smell loss affects nutrition and eating behaviour, social and psychological wellbeing, and the ability to detect environmental hazards like smoke or gas. People with anosmia report significantly higher rates of depression, anxiety, and social isolation. The loss of the ability to smell a partner, a child, or a familiar place can sever emotional connections in ways that are difficult to overstate.

For a long time, the review notes, smell was treated as the neglected stepbrother of human sensory abilities. COVID-19, for all its devastation, at least forced a reckoning with how much we had been taking it for granted.

The Bottom Line

Your sense of smell is the oldest and most direct of your senses, with a neurological architecture that bypasses conscious processing and reaches the emotional core of your brain first. It encodes your most vivid memories, shapes your emotional life, and may be one of the most sensitive early indicators of neurological health that medicine has yet to fully deploy.

If you notice an unexplained change in your sense of smell, it is worth paying attention to, and mentioning to your doctor. If your sense of smell is intact, it may be worth doing something most of us never think to do: using it deliberately, and protecting it.

Subscribe to The Health Insider newsletter where you’ll find many more insights – delivered straight to your inbox.

~ Read more from The Health Insider ~

The information provided on TheHealthInsider.ca is for educational purposes only and does not substitute for professional medical advice. TheHealthInsider.ca advises consulting a medical professional or healthcare provider when seeking medical advice, diagnoses, or treatment. To read about our editorial review process click here.

0 Shares:
Share
Tweet
Share
Share

— Previous article

A One-Time Gene Edit Could Lower Cholesterol for Life. Here's Where the Science Actually Stands.

Next article —

Peptides and You: How to Safely Benefit From These Important Amino Acids

You May Also Like
Brain Care Score
Read More
  • 3 minute read
B Brain

Get Your Brain Care Score and Boost Longevity

  • 2025-01-03
Your brain health shapes your quality of life and longevity. The McCance Brain Care Score offers a roadmap to reduce risks of dementia and depression through measurable lifestyle improvements. Take control of your brain’s future today.