Why do the elderly lose their sense of smell? Understanding the causes

According to the National Institute on Deafness and Other Communication Disorders (NIDCD), approximately one in four Americans over the age of 40 reports some alteration in their sense of smell. The prevalence of smell impairment increases significantly with age, leading many to wonder, "Why do the elderly lose their sense of smell?" This phenomenon, known as presbyosmia, is driven by a combination of natural aging processes, cumulative environmental damage, and underlying health conditions.

Quick Summary

The decline in the sense of smell among the elderly is caused by age-related deterioration of the olfactory system, compounded by long-term environmental exposures, chronic inflammation, certain medications, and neurodegenerative diseases.

Key Points

• Normal aging of the olfactory system: The olfactory epithelium thins, and the number of olfactory neurons and their regenerative capacity decrease with age, leading to a natural decline in the sense of smell.

• Cumulative environmental damage: Repeated viral infections, long-term smoking, and exposure to airborne toxins over a lifetime contribute significantly to the deterioration of the olfactory system.

• Link to neurodegenerative diseases: Loss of smell is an early and prominent symptom of diseases like Alzheimer's and Parkinson's, often appearing years before other clinical signs.

• Impact of nasal and sinus issues: Chronic inflammation from conditions like allergies, sinusitis, or nasal polyps can physically obstruct the pathway of odor molecules to the receptors.

• Medication side effects: Many common medications for older adults, including certain blood pressure drugs and antibiotics, can cause altered or reduced olfactory function.

• Reduced safety and quality of life: A poor sense of smell decreases the ability to detect hazards like smoke or spoiled food and can lead to a reduced enjoyment of eating, sometimes resulting in malnutrition.

• Potential for management: While there is no cure for natural age-related smell loss, addressing treatable underlying conditions, discontinuing offending medications, and using olfactory training can help in some cases.

The decline in olfactory function, known as presbyosmia, is a complex and multifactorial process. While it is a normal part of aging, a variety of contributing factors accelerate or exacerbate the loss of smell in older adults. Understanding these mechanisms is crucial for managing the impact on quality of life, nutrition, and safety.

Normal aging of the olfactory system

As the body ages, the intricate sensory system responsible for detecting odors undergoes several natural changes. This involves a reduction in olfactory neurons in the nasal cavity and decreased neurogenesis. The olfactory bulb in the brain, which processes smell information, also shows age-related changes, reducing the ability to interpret odors. Additionally, decreased nasal mucus production and structural changes in the nasal passages can hinder odor detection.

Environmental and lifestyle factors

Beyond natural aging, external factors and lifestyle choices contribute to smell loss. Repeated viral infections, such as colds, the flu, or COVID-19, can cause cumulative damage to the olfactory system, which seniors are less able to recover from. Chronic smoking is a significant risk factor due to the damage caused by toxins, though quitting may help. Long-term exposure to chemicals like pesticides can also harm the olfactory system. Head or facial injuries can damage the olfactory nerve fibers or brain regions involved in smell, with potentially more severe consequences in older adults.

Medical conditions and medications

Several health conditions common in older age can affect smell. Loss of smell is an early symptom of neurodegenerative diseases like Alzheimer's and Parkinson's. Chronic nasal and sinus issues, including allergies and polyps, can cause inflammation and block odor pathways. Many medications prescribed to seniors, such as antibiotics and blood pressure drugs, can cause taste and smell disturbances as a side effect. Other conditions like diabetes and nutritional deficiencies can also impair olfactory function.

Comparison of age-related vs. disease-related smell loss

Age-related smell loss (presbyosmia) is a gradual decline, while disease-related loss can be more sudden and linked to specific conditions. The severity and symmetry of smell loss can also differ depending on the cause. The table below compares these forms of olfactory impairment.

Feature	Age-Related Loss (Presbyosmia)	Disease-Related Loss
Onset	Gradual, often starting after age 60, and unnoticed by the individual initially.	Can be rapid, sudden, or linked to the onset of other symptoms, such as with a viral infection or neurodegenerative disease.
Severity	Typically a progressive but mild to moderate reduction in the ability to detect and identify odors.	Can range from mild to complete loss (anosmia), depending on the underlying condition.
Symmetry	Generally affects both nostrils and is symmetric, though the degree may vary.	Can be symmetric or asymmetric, depending on the specific disease (e.g., nasal polyps may affect one side more than the other).
Underlying Cause	Natural deterioration of the olfactory system, including reduced neural regeneration, thinning epithelium, and changes in the olfactory bulb.	Caused by specific pathologies such as viral damage, inflammation, nasal obstruction, or neurological disorders.
Associated Symptoms	Rarely accompanied by other sudden neurological symptoms, but may affect appetite and dietary habits.	Often associated with other neurological signs (motor, cognitive), nasal congestion, or systemic symptoms.

Consequences and management

Loss of smell can have serious consequences for the elderly, including reduced safety due to inability to detect hazards like gas leaks or smoke. It can also lead to poor nutrition, weight loss, and potentially depression as food becomes less enjoyable. Treatment depends on the cause; for example, treating sinus infections or switching medications may help. For age-related or neurodegenerative causes, there may not be a cure, and management focuses on safety and exploring options like olfactory training.

Conclusion

The decline in smell among the elderly is a result of multiple factors, including natural aging, environmental exposures, and age-related diseases. While some loss is normal, significant changes warrant medical evaluation to identify treatable causes and address safety concerns. The link between olfactory dysfunction and neurodegenerative disease highlights the importance of monitoring smell function in older adults.

For more information on the anatomy of the olfactory system and age-related changes, see the Handbook of Clinical Neurology.

Frequently Asked Questions

Is it normal for elderly people to lose their sense of smell completely?

While a gradual decline is normal, a complete loss of smell (anosmia) is not. It could be a sign of an underlying medical condition, such as a severe sinus infection, nasal polyps, or a neurodegenerative disease, and should be evaluated by a doctor.

Can medications cause the elderly to lose their sense of smell?

Yes, many medications commonly used by older adults can interfere with their sense of smell. These include certain antibiotics, blood pressure medications (like ACE inhibitors), and some antihistamines. It is important to discuss any changes with a healthcare provider, who may be able to suggest an alternative.

How do neurodegenerative diseases affect an elderly person's sense of smell?

In diseases like Alzheimer's and Parkinson's, the buildup of pathological proteins and resulting neurodegeneration can damage the olfactory system and the brain regions that process smell. This often causes olfactory dysfunction very early in the disease course.

Can recovering from a viral infection cause long-term smell loss in seniors?

Yes, damage to the olfactory receptor neurons from viral infections, including COVID-19 and the common cold, is a frequent cause of both temporary and persistent smell loss. The regenerative capacity of the olfactory system diminishes with age, making recovery less likely or complete for seniors.

What are the safety risks associated with an elderly person's loss of smell?

Loss of smell, or anosmia, can reduce the ability to detect dangerous airborne signals such as a gas leak or smoke from a fire. It also increases the risk of consuming spoiled or expired food that has an off odor but appears normal.

Is there any treatment for age-related smell loss?

There is no cure for true presbyosmia, or age-related smell loss. However, treating underlying conditions like allergies or sinus infections can help. Olfactory training, which involves regular, conscious exposure to different scents, has also been shown to improve function in some cases.

Does losing the sense of smell mean losing the sense of taste?

A diminished sense of smell often affects the perception of flavor, which is a combination of both taste and smell. Many elderly people report that food tastes bland, believing their sense of taste is impaired, when in fact it is their olfactory function that is the primary issue.