Loss of smell, medically known as anosmia, is a symptom that many people first noticed during the COVID-19 pandemic. However, long before that, neurologists recognized that changes in the sense of smell can be an important sign of underlying neurological conditions.
The sense of smell is closely connected to the brain, particularly areas responsible for memory, emotion, and behavior. Because of this connection, a reduced or lost ability to smell can sometimes be an early warning sign of neurological disease.
This article provides an overview of five neurological causes of loss of smell and considerations for possible medical assessment.
1. Parkinson’s Disease
One of the earliest and most common non-motor symptoms of Parkinson’s Disease is a reduced sense of smell.
In fact, anosmia can appear years before the typical motor symptoms such as tremor or stiffness.
Why does it happen?
Parkinson’s affects brain regions involved in smell processing, particularly the olfactory bulb and related pathways.
If loss of smell is accompanied by:
- Slowness of movement
- Tremor
- Sleep disturbances
it is important to seek neurological evaluation.
2. Alzheimer’s Disease
Alzheimer’s Disease is another condition where smell loss can appear early, even before noticeable memory problems.
Why does it happen?
The disease affects areas of the brain responsible for both smell and memory, such as the hippocampus.
Difficulty identifying familiar smells (like coffee or perfume) may be an early cognitive warning sign.
3. Head Trauma (Traumatic Brain Injury)
A head injury can damage the nerves responsible for smell, leading to partial or complete anosmia.
Why does it happen?
The olfactory nerves are very delicate and can be easily injured when the brain moves within the skull during trauma.
Common causes:
- Falls
- Car accidents
- Sports injuries
Loss of smell after a head injury should always be evaluated, especially if persistent.
4. Brain Tumors Affecting the Olfactory Pathway
Certain brain tumors located in the frontal lobe or near the olfactory bulb can interfere with smell.
Why does it happen?
Tumors may compress or damage the olfactory pathways.
Warning signs:
- Persistent headaches
- Personality changes
- Vision problems
Although rare, progressive loss of smell with other neurological symptoms requires urgent assessment.
5. Multiple Sclerosis (MS)
Multiple Sclerosis is a neurological condition that can affect many sensory pathways, including smell.
Why does it happen?
Inflammation and demyelination can disrupt signal transmission in the brain regions responsible for olfaction.
Loss of smell in MS is less common but can occur alongside:
- Visual disturbances
- Numbness or tingling
- Fatigue
When Should You See a Neurologist?
You should consider medical evaluation if loss of smell:
- Appears suddenly without a clear cause
- Persists for more than a few weeks
- Is associated with memory changes or movement symptoms
- Occurs after head injury
- Progressively worsens over time
Loss of smell is often overlooked, but it can be an important neurological symptom. While many cases are due to temporary causes such as infections, persistent anosmia may indicate an underlying brain-related condition.
Early evaluation can lead to earlier diagnosis—and in many neurological diseases, early intervention makes a significant difference.
A proper neurological assessment can provide clarity, reassurance, and, when necessary, timely treatment.