Understanding Persistent Olfactory Dysfunction After COVID-19
For many who have recovered from the acute phase of COVID-19, the journey to full health continues long after the virus is gone. One of the most common and frustrating lingering symptoms is olfactory dysfunction—the loss or alteration of the sense of smell. While often dismissed as a minor inconvenience, recent research suggests that persistent smell loss may be linked to deeper neurological changes and cognitive risks.
- Olfactory dysfunction can persist for months or years after a SARS-CoV-2 infection.
- Many patients have a weaker sense of smell than they realize, even if they believe their smell is normal.
- Persistent smell loss is associated with structural changes in brain regions like the amygdala.
- There is a potential link between long-term olfactory deficits and cognitive or memory issues.
The Reality of Long-Term Smell Loss
Olfactory dysfunction is a hallmark of COVID-19, but its persistence varies. While the majority of people recover their sense of smell, a notable subset experiences symptoms that last longer than three months, categorizing them as long-haul COVID-19 patients.
A significant challenge in diagnosing this condition is that patients often underestimate the severity of their loss. According to a study conducted by the RECOVER adult cohort, researchers used the University of Pennsylvania Identification Test (UPSIT)—a “scratch-and-sniff” test—to objectively measure smell. The findings were revealing:
- Confirmed Loss: 8 out of 10 people who reported changes in their smell were confirmed to have abnormal olfactory function.
- Hidden Deficits: Two-thirds of participants who believed their sense of smell was completely normal actually had a weaker sense of smell than they realized.
Neurological Impact and Brain Connectivity
Researchers are moving beyond the nasal cavity to understand why some people don’t recover. Evidence suggests the central nervous system is involved. A study published in Nature used diffusion tensor imaging (DTI) to examine the brain’s white matter pathways in patients with persistent post-COVID olfactory dysfunction (PC-OlfDys).
The study found significant structural changes in the amygdala, a brain region involved in both olfactory processing and emotional regulation. Specifically, patients with persistent smell loss showed higher fractional anisotropy (FA) in the left amygdala and higher radial diffusivity (RD) in the right amygdala compared to normosmic controls. These changes suggest alterations in the myelination or axonal diameter of olfactory-related brain regions.
The Link to Mental Health and Cognition
The amygdala, along with the putamen and piriform cortex, is tied to emotional well-being. The research noted that patients with post-COVID olfactory dysfunction as well exhibited higher scores for depression and anxiety. While the exact direction of this relationship is still being studied, it suggests that smell loss and emotional distress may be interrelated.
because olfactory changes have been linked to memory and thinking problems in other medical conditions, there is concern that those with persistent COVID-related smell loss may be at a higher risk for cognitive deficits.
Why Objective Testing Matters
Because many patients are unaware of the extent of their smell loss, clinical reliance on patient self-reporting can be misleading. Objective testing is critical for two primary reasons:
- Safety: A diminished sense of smell increases the risk of undetected hazards, such as smoke or spoiled food.
- Early Intervention: Identifying smell loss allows doctors to better understand a patient’s condition and monitor for associated cognitive or psychological risks.
Frequently Asked Questions
How long does COVID-19 smell loss typically last?
While it is transient for most, some individuals experience ongoing symptoms for months or even years after the initial infection.
Can I have a smell deficit if I perceive my smell is normal?
Yes. Research indicates that a large portion of people who believe their sense of smell is normal actually exhibit a weakened sense of smell when tested objectively.
Is there a connection between smell loss and brain health?
Yes, studies have shown structural changes in the amygdala in patients with persistent smell loss and such dysfunction has been associated with cognitive loss in other conditions.
Looking Ahead
As we continue to study the long-term effects of SARS-CoV-2, the focus is shifting toward the intersection of sensory loss and neurological health. Understanding the structural changes in the brain may eventually lead to more targeted therapies to help long-haul patients recover their senses and protect their cognitive function.
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