Reviewed by the Help Dementia Editorial Team — our editors review every article for accuracy against guidance from the National Institute on Aging, the Alzheimer’s Association, and peer-reviewed sources.
Early dementia sits at the center of this dementia and brain health question.
Yes, the loss of sense of smell can be an early warning sign of dementia, according to research from neurologists and cognitive specialists. A growing body of evidence suggests that olfactory dysfunction—the medical term for impaired smell—often precedes the cognitive decline associated with Alzheimer’s disease and other forms of dementia by several years. When someone begins to notice they can no longer smell their morning coffee, detect spoiled food, or perceive familiar scents like a loved one’s perfume, this sensory change warrants medical attention, as it may indicate changes occurring in brain regions critical for both smell and memory. The connection between smell and dementia is grounded in neurology.
The olfactory system—the biological pathways involved in smell—connects directly to the brain’s limbic system, which includes the hippocampus and entorhinal cortex. These are among the first brain structures to show damage in Alzheimer’s disease. When dementia begins to develop, pathological changes in these regions can impair the olfactory nerve’s function before a person experiences memory loss or cognitive confusion. This makes smell testing a potential screening tool that neurologists are increasingly considering in clinical practice.
Table of Contents
- How Does Loss of Smell Signal Early Dementia Risk?
- The Science Behind Olfactory Dysfunction in Dementia
- Why the Olfactory System Reveals Brain Changes Early
- How to Get Smell Function Tested and What It Means
- Age-Related Smell Loss Versus Dementia-Related Loss
- The Role of Smell in Memory and Emotional Function
- The Future of Smell Testing in Dementia Screening
- Conclusion
- Frequently Asked Questions
How Does Loss of Smell Signal Early Dementia Risk?
The olfactory system’s proximity to memory centers in the brain creates a unique vulnerability. Unlike most other senses, the olfactory nerve connects directly to the prefrontal cortex and hippocampus without passing through the thalamus, a relay station in the brain. When neurodegenerative processes begin, the hippocampus and entorhinal cortex are often affected first, and this damage disrupts the olfactory system’s function. Research published in neurological journals has shown that individuals with reduced smell sensitivity are significantly more likely to develop cognitive impairment within five to ten years compared to those with normal olfactory function.
A practical example illustrates this connection: a 68-year-old woman who had always cooked with fresh herbs suddenly reported to her family that she could no longer smell them while cooking. Within three years, she began experiencing mild cognitive impairment, eventually receiving an Alzheimer’s diagnosis. Her daughter later reflected that the loss of smell had been the first concrete sign that something was changing in her mother’s brain. Studies suggest that roughly half of people who experience a significant decline in smell sense and have no other explanation for it may go on to develop mild cognitive impairment or dementia within a decade.
The Science Behind Olfactory Dysfunction in Dementia
Neuroimaging studies have revealed that dementia-related brain damage in the olfactory regions follows a pattern similar to what researchers see in memory-related brain areas. The entorhinal cortex, which is crucial for both smell perception and the formation of new memories, shows atrophy and tau protein accumulation in Alzheimer’s disease. However, a critical limitation of using smell loss as a screening tool is that many other conditions can also impair smell—including COVID-19, Parkinson’s disease, normal aging, chronic sinusitis, and certain medications. This means that smell loss alone cannot diagnose dementia; it is one potential indicator among many that warrants further medical evaluation.
Another important distinction: not all dementia causes olfactory dysfunction equally. Alzheimer’s disease shows the strongest association with smell loss, while other types of dementia, such as vascular dementia, may not affect the olfactory system as directly. Additionally, some individuals in the early stages of dementia retain relatively normal smell function, which means the absence of smell loss does not rule out cognitive decline. Neurologists emphasize that smell testing is most useful as part of a comprehensive neurological evaluation that includes cognitive testing, imaging, and assessment of other neurological functions.
Why the Olfactory System Reveals Brain Changes Early
The olfactory bulb—the structure that processes smell signals—is one of the few brain regions where new neurons are born throughout life, a process called neurogenesis. This makes the olfactory system particularly sensitive to neurodegenerative changes. When the pathological hallmarks of Alzheimer’s disease, including amyloid-beta plaques and tau tangles, begin to accumulate in the brain, the olfactory system is often among the first areas affected. The vulnerability of this system stems from the fact that olfactory neurons are exposed directly to the environment and may be more susceptible to oxidative stress and inflammation.
A specific example comes from longitudinal studies tracking older adults over many years. researchers found that seniors who scored in the bottom 25 percent on smell tests were three to five times more likely to develop dementia than those who scored in the top 25 percent. In one notable study, participants who could not identify at least four out of five common odors had significantly faster rates of cognitive decline. This pattern held even when researchers controlled for age, education, and other factors that influence dementia risk.
How to Get Smell Function Tested and What It Means
If someone suspects a decline in their ability to smell, the first step is to see a primary care physician or neurologist to rule out non-neurological causes, such as nasal obstruction, sinus infection, or medication side effects. The University of Pennsylvania Smell Identification Test (UPSIT) is a standardized assessment that neurologists use clinically. This test presents a patient with forty odor-saturated strips and asks them to identify the smell among multiple-choice options. The results are compared to age-appropriate norms.
The tradeoff in smell testing is that while it can help identify people at higher risk for dementia, it is not a definitive diagnostic test. Someone with poor smell function may live many years without developing cognitive decline, while someone with normal smell may later develop dementia. This uncertainty means that a positive smell test should prompt further investigation—including cognitive testing, medical imaging such as an MRI, and discussion of family history—rather than alarm. A person who notices smell loss should view it as an opportunity to establish a baseline of their cognitive and sensory function with their healthcare provider, allowing for monitoring over time.
Age-Related Smell Loss Versus Dementia-Related Loss
As people age naturally, their sense of smell diminishes. This normal age-related decline affects roughly 50 percent of people over age 65 and up to 75 percent over age 80. This widespread change makes it difficult to distinguish normal aging from smell loss that signals disease. However, neurologists note that the pattern and severity of smell loss can provide clues. Dementia-related olfactory dysfunction typically involves an inability to identify odors (called olfactory identification impairment) rather than simply reduced smell intensity.
A person might detect that something has a smell but cannot identify what it is—they might know their kitchen smells like something burning but cannot recognize it as coffee. A warning regarding self-assessment: older adults should not attempt to diagnose themselves based on anecdotal observations of smell changes. Some people who believe they have lost their sense of smell actually have a diminished ability to identify odors while still detecting them, which requires standardized testing to confirm. Additionally, seasonal variations in smell function and recent viral infections can temporarily impair smell, and these temporary changes do not necessarily indicate neurodegeneration. The key is whether smell loss is persistent, progressive, and accompanied by other neurological changes that warrant professional evaluation.
The Role of Smell in Memory and Emotional Function
The olfactory system’s connection to memory is so direct that smell is often called the most evocative sense. A particular fragrance can instantly transport someone to a childhood memory or emotional moment, bypassing the logical, language-based parts of the brain. This connection exists because the olfactory bulb projects directly to the limbic system, including the amygdala and hippocampus, which process emotion and memory.
When dementia damages these structures, the loss of smell compounds cognitive decline because patients lose not only the sensory experience but also a powerful memory trigger. For example, an Alzheimer’s patient who had always been moved by the smell of her grandmother’s rose garden might eventually fail to recognize the scent at all. This loss is not trivial from a quality-of-life perspective; smell contributes to enjoyment of food, detection of hazards, and emotional wellbeing. Caregivers working with dementia patients increasingly recognize that supporting olfactory experiences—whether through pleasant scents, cooking with aromatic foods, or discussing smell memories—can provide comfort and engagement even as cognitive abilities decline.
The Future of Smell Testing in Dementia Screening
Researchers are working to integrate olfactory assessment into routine cognitive screening for older adults. Some neurology centers now include smell testing as part of standard dementia workups, recognizing that it can identify at-risk individuals who might benefit from earlier intervention. As researchers develop new treatments targeting early dementia—including drugs that may slow cognitive decline—identifying people in the earliest stages becomes increasingly important.
A simple smell test could serve as a low-cost, non-invasive gateway to further evaluation and potential disease-modifying treatment. Looking forward, the field is moving toward a more nuanced understanding of how olfactory dysfunction relates to different types of dementia and how quickly smell loss progresses in at-risk individuals. Advances in neuroimaging may eventually allow researchers to identify the specific brain changes causing smell loss in a given person, enabling more personalized predictions about dementia risk. Until then, healthcare providers advise that unexplained smell loss warrants attention—not panic, but careful medical follow-up as part of a proactive approach to brain health.
Conclusion
Loss of sense of smell can be an early indicator of dementia, particularly Alzheimer’s disease, because the olfactory system connects directly to brain regions that are among the first to show neurodegenerative changes. While smell loss alone cannot diagnose dementia—and many other conditions cause olfactory dysfunction—persistent, progressive impairment in smell identification warrants medical evaluation. The significance of this finding lies in its potential to identify people in the earliest stages of cognitive decline, when interventions may be most effective.
Anyone who notices a gradual, unexplained decline in their ability to smell should discuss this change with their healthcare provider. A neurologist can assess whether the smell loss reflects normal aging, a treatable medical condition, or a potential sign of cognitive change. Early awareness combined with appropriate medical monitoring supports better health outcomes and allows individuals and their families to plan ahead if cognitive decline is occurring.
Frequently Asked Questions
Is it normal to lose my sense of smell as I age?
Some decline in smell is normal with age—about half of people over 65 experience some reduction in smell. However, a sudden or marked decline, or persistent difficulty identifying odors, is different from normal aging and should be evaluated by a healthcare provider.
Does everyone with dementia lose their sense of smell?
No. While smell loss is common in Alzheimer’s disease, not everyone with Alzheimer’s or other dementias experiences olfactory dysfunction. Smell loss is one potential early sign, but its absence does not rule out dementia.
How is smell function tested?
Standardized tests like the University of Pennsylvania Smell Identification Test (UPSIT) present odor-saturated strips and ask patients to identify scents from multiple-choice options. Your doctor can order this test, which takes about 10-15 minutes.
What should I do if I notice I’ve lost my sense of smell?
Schedule an appointment with your primary care doctor or a neurologist. They can rule out common causes like sinus infection or medication side effects and determine whether further cognitive evaluation is warranted.
Could smell loss be from COVID-19 instead of dementia?
Yes. COVID-19, viral infections, and sinus problems commonly cause smell loss. This is why medical evaluation is essential—your doctor can differentiate between temporary smell loss from infection and persistent loss that might signal neurological changes.
At what age should I be concerned about smell loss as a dementia sign?
The association between smell loss and dementia risk increases significantly after age 60. If you’re in this age range and notice unexplained smell loss, discussing it with your healthcare provider is prudent.
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For more, see Alzheimer’s Association — clinical trials.
