Loss of Smell: An Overlooked Symptom That May Signal Serious Disease

25th September 2025

2 minutes read

Loss of Smell: An Overlooked Symptom That May Signal Serious Disease

Loss of smell, or anosmia, is often considered a minor or temporary issue, commonly linked to respiratory infections or seasonal colds. However, recent research in neurology and general medicine indicates that this symptom may sometimes signal far more serious conditions, including certain neurodegenerative diseases and systemic disorders.

Anosmia and neurodegenerative diseases

Several scientific studies have highlighted a strong connection between smell loss and neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. In Parkinson’s disease, anosmia can precede motor symptoms, such as tremors or muscle rigidity, by several years. Researchers report that approximately 90% of Parkinson’s patients experience olfactory impairment before a clinical diagnosis is made.

In Alzheimer’s disease, gradual loss of olfactory perception can serve as an early indicator. Standardized olfactory tests can detect these anomalies and help predict the risk of cognitive decline, providing a critical window for early intervention.

Possible causes and biological mechanisms

Anosmia may result from a variety of causes, ranging from viral infections to head trauma. Physiologically, it is often linked to damage to the olfactory receptors in the nasal mucosa or to disruptions in the neural pathways leading to the olfactory bulb and cerebral cortex. In neurodegenerative diseases, pathological protein deposits, such as alpha-synuclein in Parkinson’s disease or amyloid plaques in Alzheimer’s disease, interfere with olfactory signal transmission.

Anosmia and other serious diseases

Beyond neurodegenerative disorders, loss of smell can also indicate other serious medical conditions:

Endocrine disorders: thyroid dysfunction or poorly controlled diabetes can impair smell perception.
Severe infections: certain viral infections, including COVID-19, have shown that sudden anosmia can be the first sign of illness.
Brain tumors: tumors near the olfactory bulb or olfactory pathways may cause partial or total smell loss.
Cardiovascular and metabolic diseases: recent studies suggest that anosmia may be associated with an increased risk of cardiovascular mortality and metabolic decline.

Screening and diagnosis

Early anosmia diagnosis relies on a thorough clinical examination and standardized smell tests, such as the University of Pennsylvania Smell Identification Test (UPSIT). These tests quantify olfactory loss and detect subtle anomalies. Brain imaging, such as MRI, may be required if neurological or tumor-related pathology is suspected.

Prevention and management

While specific prevention of anosmia is challenging, early recognition of the symptom is critical to limit the progression of serious diseases. Therapeutic approaches include:

Treating the underlying cause: for example, correcting hormonal imbalances or managing infections.
Olfactory rehabilitation: progressive olfactory training designed to stimulate sensory receptors and neural pathways.
Regular medical follow-up: particularly for patients with neurological or cardiovascular risk factors.

Loss of smell should never be overlooked, especially when it occurs suddenly or persists. This seemingly minor symptom may serve as the first warning sign of serious illnesses, including neurodegenerative and cardiovascular diseases. Raising awareness among the public and healthcare professionals about the importance of anosmia is essential for enabling early diagnosis and appropriate interventions.