Creator: Help Dementia Editorial Team
Published: 2026-04-26T11:20:47

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.

Smell behavior sits at the center of this dementia and brain health question.

Yes, a significant loss of sense of smell and noticeable personality changes may indeed signal the earliest stages of dementia, sometimes appearing years before memory problems become apparent. Olfactory loss is one of the earliest detectable signs of Alzheimer’s disease, with immune cells beginning to destroy smell-related nerve fibers in the brainstem during early disease stages. When these warning signs appear together—or even in isolation—they warrant attention from healthcare providers who can monitor cognitive health and begin conversations about brain health strategies.

Consider the case of a 68-year-old who suddenly can’t taste her morning coffee or notice the smell of rain, while simultaneously becoming more withdrawn and irritable with family members. Her family might assume these are separate, minor issues related to aging. In reality, both changes can be manifestations of early neurological changes associated with dementia risk. This convergence of sensory and behavioral shifts is what researchers are increasingly focusing on as they work to identify dementia in its earliest, most treatable stages.

How Are Loss of Smell and Behavior Changes Connected to Early Dementia?
What Is Mild Behavioral Impairment and Why Does It Matter?
Can Smell Tests Reliably Predict Cognitive Decline?
How Should Family Members Respond When They Notice These Signs?
Important Limitations and Cautions When Interpreting These Signs
The Importance of Baseline Assessment and Ongoing Monitoring
Looking Forward—What Research Is Revealing About Early Detection
Conclusion

How Are Loss of Smell and Behavior Changes Connected to Early Dementia?

The connection between olfactory loss and dementia risk is substantial and well-documented in recent research. A 12-year Swedish population-based study found that anosmia—complete loss of smell—increases dementia risk by nearly threefold. This isn’t coincidental; the brainstem regions involved in smell processing are among the first areas affected by the pathological changes underlying Alzheimer’s disease. When immune cells begin attacking smell-related nerve fibers, it’s often a sign that similar damage is occurring elsewhere in the brain. Behavioral changes operate on a similar timeline. personality and behavioral shifts—including apathy, irritability, loss of empathy, and reduced social interest—can appear before memory problems emerge.

Researchers at UCI MIND have documented that these personality shifts often precede cognitive symptoms by months or even years. A spouse might notice their partner withdrawing from social activities they once enjoyed, becoming uncharacteristically argumentative, or showing diminished concern for family members’ wellbeing. These aren’t character flaws or normal aging; they’re potential neural warning signals. What makes this particularly significant is that neither symptom requires obvious cognitive decline to be meaningful. Someone experiencing olfactory loss and mild personality changes might score normally on standard memory tests. Yet their brain may already be undergoing the pathological changes associated with dementia development. This is why healthcare providers are increasingly trained to view these seemingly minor changes as potentially serious clinical markers.

How Are Loss of Smell and Behavior Changes Connected to Early Dementia?

What Is Mild Behavioral Impairment and Why Does It Matter?

Researchers have identified a specific pattern called Mild Behavioral Impairment (MBI)—defined as new, sustained personality changes lasting six months or longer that occur in the absence of significant cognitive decline. MBI is not simply “acting a little different”; it represents a notable deviation from a person’s established baseline personality and behavior patterns. Someone who was naturally sociable becomes withdrawn. Someone typically patient becomes quick to anger. These changes are both noticeable and sustained. The clinical importance of recognizing MBI cannot be overstated.

Studies show that people with more neuropsychiatric symptoms during mild cognitive impairment are significantly more likely to progress to dementia. This means that early detection and monitoring of behavioral changes can help identify individuals at highest risk of disease progression. However, a crucial limitation exists: not everyone with behavioral changes will develop dementia, and not everyone who develops dementia will show obvious behavioral changes first. Some individuals progress primarily through cognitive pathways. This is why behavioral observation should never be used as a standalone diagnostic tool but rather as one piece of a comprehensive assessment. Another important caution: behavioral changes can stem from multiple sources—depression, anxiety, medication side effects, sleep disorders, or hormonal changes. A comprehensive evaluation by a healthcare provider is essential to distinguish between MBI potentially related to dementia and behavioral changes from other treatable conditions.

Can Smell Tests Reliably Predict Cognitive Decline?

The predictive power of olfactory testing is surprisingly robust. Research from the National Institute on Aging found that each point lower on odor identification tests correlated with a 22 percent higher risk of developing mild cognitive impairment. A person who scores five points lower on a smell test than they did five years earlier faces a dramatically elevated risk profile. Even more striking, rapid decline in sense of smell predicted Alzheimer’s-related brain changes, including smaller gray matter volume, with predictive value equivalent to carrying the APOE-e4 genetic risk factor—one of the strongest known dementia risk factors. Conversely, maintaining a good sense of smell is associated with slower brain volume loss and cognitive decline in older adults. This suggests that olfactory function isn’t merely a marker of disease but may reflect underlying brain health more broadly.

When someone’s smell remains sharp, their brain tissue is often holding up better against age-related changes. When smell declines rapidly, it signals that neural changes are accelerating. However, smell testing has practical limitations. The specific tests used vary between healthcare settings, making it difficult to compare results across providers. Cultural and environmental factors influence smell sensitivity—someone who grew up in a rural area may have different baseline olfactory abilities than someone from an urban environment. Additionally, other conditions affecting smell exist beyond dementia: nasal polyps, chronic sinusitis, COVID-19 related anosmia, and smoking all diminish olfactory function. A single poor smell test score doesn’t diagnose dementia; rather, rapid decline in smell, tracked over time, provides meaningful clinical information.

Can Smell Tests Reliably Predict Cognitive Decline?

How Should Family Members Respond When They Notice These Signs?

The first step is documentation. If you’re noticing personality changes or a family member’s sense of smell declining, keep a simple written record: when did you first notice this? What specifically changed? Has it progressed? This information is invaluable to healthcare providers who can’t be present during daily family interactions. Rather than relying on memory alone—which can be colored by emotion or recent events—a written timeline provides objective evidence. The second step is a comprehensive medical evaluation. Schedule an appointment with the person’s primary care physician and share your observations directly. Come prepared with specific examples: “Mom used to call friends weekly for lunch; now she says she doesn’t feel like socializing” is more clinically useful than “Mom seems withdrawn.” Request that smell be assessed, either through formal odor identification testing or simple bedside evaluation.

Request baseline cognitive screening, which might include brief tools like the Montreal Cognitive Assessment (MoCA) or Mini-Cog. If a baseline is established now, future testing can measure change accurately. One important tradeoff exists in early detection: knowing about dementia risk early allows for interventions that may slow progression, but it also carries psychological weight. The person being evaluated may experience anxiety or depression in response to concerning findings. Balancing the value of early detection against the emotional toll of potential bad news is a legitimate family discussion. Some families choose to pursue aggressive evaluation and early intervention; others prefer a more watchful approach. There’s no universally right answer, only what feels appropriate for each family’s values and circumstances.

Important Limitations and Cautions When Interpreting These Signs

Not everyone with olfactory loss will develop dementia. Many people experience smell decline as a simple function of normal aging or treatable conditions. Similarly, personality changes can reflect depression, medication effects, or other medical conditions entirely unrelated to dementia. The danger in recognizing these signs is over-pathologizing normal aging or treatable conditions. A 75-year-old with some smell loss and occasional irritability does not necessarily have early dementia—they might have seasonal allergies and be frustrated with a recent medication change. The predictive research cited here describes population-level associations, not individual fate. When a study says “anosmia increases dementia risk threefold,” it means that among people with anosmia, dementia rates are threefold higher than the general population. It does not mean that anyone with anosmia will definitely develop dementia.

Many people with smell loss live out their lives without cognitive decline. Statistical significance in research doesn’t equal clinical certainty for any individual person. This distinction is crucial for avoiding unnecessary anxiety or overmedicalizing normal aging. Additionally, these early signs appear more clearly in certain dementia types than others. Olfactory loss is particularly prominent in Alzheimer’s disease but less so in some other forms of dementia like vascular dementia or frontotemporal dementia. Behavioral changes are more characteristic of frontotemporal dementia than Alzheimer’s disease. A person might show one warning sign strongly while other markers remain absent, yet still be experiencing meaningful neurological changes. This complexity is precisely why evaluation requires expert clinical judgment rather than self-diagnosis based on symptoms alone.

Important Limitations and Cautions When Interpreting These Signs

The Importance of Baseline Assessment and Ongoing Monitoring

One of the most valuable things families can do is establish a baseline of cognitive and olfactory function early, particularly for those with dementia risk factors (family history, age over 60, cardiovascular disease). This baseline becomes the reference point for detecting meaningful change over time. Many primary care physicians can perform basic cognitive screening, and smell assessment requires only a simple odor identification test, available at many healthcare settings. Once a baseline is established, periodic reassessment—perhaps annually or every two years—allows providers to track trajectories.

Someone whose smell declines slightly over five years follows a different clinical path than someone whose smell collapses over six months. Change over time matters more than absolute scores. A person with a lifelong poor sense of smell who remains stable is different from someone with normal smell who experiences rapid decline. This is why ongoing monitoring, rather than single-point evaluation, provides the most clinically useful information for predicting cognitive risk.

Looking Forward—What Research Is Revealing About Early Detection

The convergence of olfactory loss, behavioral changes, and neuroimaging findings is reshaping how researchers and clinicians approach dementia prevention. Rather than waiting for memory loss to signal the disease, the field is increasingly focused on identifying people in the preclinical stage—those with brain changes but no obvious symptoms. This shifts the therapeutic window, potentially allowing interventions when the brain is most responsive to protective strategies.

Emerging research also suggests that maintaining robust olfactory function—through olfactory enrichment, diverse sensory experiences, and overall brain health—may help preserve cognitive function into older age. While no intervention has been proven to prevent dementia outright, maintaining cardiovascular health, cognitive engagement, physical activity, and social connection all correlate with slower cognitive decline. These lifestyle factors don’t just support brain health directly; they may also help maintain the olfactory and emotional regulation systems that serve as early warning systems for neurological decline.

Conclusion

Loss of sense of smell and personality changes can be early indicators of dementia, sometimes appearing years before cognitive decline becomes noticeable. The research demonstrating this connection is robust and increasingly specific: olfactory loss predicts brain changes with power equivalent to major genetic risk factors, and behavioral changes during the early cognitive decline phase predict progression to dementia. However, these signs are not certain indicators—they warrant evaluation and monitoring rather than immediate diagnosis or panic.

The most practical response is straightforward: if you notice rapid smell loss in yourself or a family member, or if you observe sustained personality changes that represent a meaningful shift from baseline, discuss these with a healthcare provider. Establish a baseline for both cognitive function and olfactory ability. Track changes over time rather than focusing on any single moment. This combination of awareness, evaluation, and ongoing monitoring positions families to catch significant neurological changes early, when interventions may be most beneficial, while avoiding the overdiagnosis and anxiety that can accompany identifying risk factors in otherwise healthy aging.