Can loss of smell diagnose Parkinson’s disease or Alzheimer’s disease?

No. Smell loss can be an early feature in research on Parkinson’s disease and Alzheimer’s disease, but it is non-specific. Common causes include infections, sinusitis, allergies, nasal polyps, medicines and ageing. A smell change cannot diagnose either condition.

When should I speak to my GP about a change in smell?

The NHS advises speaking to a GP if your sense of smell does not return to normal in a few weeks. Assessment is also appropriate for persistent, unexplained or progressively worsening changes, or when other concerning symptoms are present.

Can I test my sense of smell at home?

You can notice whether familiar smells such as coffee, citrus, soap or herbs seem different from normal for you. This may help you notice change, but a homemade test cannot determine the cause or screen you reliably for Parkinson’s disease, Alzheimer’s disease or dementia.

What is smell training?

Smell training involves repeated exposure to a small set of distinct odours over time. It may help some people with post-viral or other smell dysfunction, but it is not established as a way to prevent Parkinson’s disease, Alzheimer’s disease or dementia.

Why does smell matter for healthy ageing?

Smell contributes to flavour, appetite, enjoyment of food, memory, emotion and safety. A significant smell change can affect eating and make smoke, gas or spoiled food harder to detect, so practical safety measures and appropriate clinical advice remain important.

Measure · Age Watchers article

Could Your Sense of Smell Tell You Something About Your Health?

We usually notice our sense of smell only when it disappears. But researchers are increasingly interested in smell as a potential early marker of conditions including Parkinson's and Alzheimer's disease. The science is intriguing — but a poor sense of smell can mean many different things.

We measure blood pressure, weight, steps, heart rate and sleep. But almost nobody wakes up thinking: “How’s my sense of smell today?”

Usually, we only notice smell when something changes. Coffee suddenly smells weak. Food tastes strangely bland. Perfume disappears. Familiar smells no longer seem familiar.

Often the explanation is ordinary. But scientists are increasingly interested in another possibility: could changes in smell sometimes provide an early clue that something deeper is changing?

MEASURE.
UNDERSTAND.
IMPROVE.
MAINTAIN.

Why smell matters more than we think

Smell contributes to flavour, appetite, enjoyment of food, memory and emotion. It also helps keep us safe by alerting us to smoke, gas and food that has gone off.

The olfactory system has close connections with brain regions involved in memory and emotion. That anatomical relationship is one reason researchers are interested in smell and brain health. But a connection between systems is not proof that a smell change diagnoses a brain condition.

What counts as a smell problem?

The NHS uses several terms:

Anosmia: loss of smell.
Hyposmia: a reduced sense of smell.
Parosmia: smells that have changed or become distorted.
Phantosmia: smelling something that is not actually present.

Some reduction in smell also becomes more common as people get older. The pattern, timing and context matter much more than a single impression.

The common causes come first

According to current NHS guidance, smell changes are most often caused by illnesses such as a cold, flu or COVID-19, sinusitis, allergies such as hay fever, or nasal polyps. Some medicines can also affect smell.

So a change in smell does not automatically mean a neurological disease. Most explanations are considerably more ordinary.

A health signal is not the same thing as a diagnosis.

Why Parkinson’s researchers care about smell

Loss or reduction of smell is common in Parkinson’s disease. Research suggests that olfactory dysfunction can appear years before the characteristic movement symptoms, which makes it a potentially important prodromal feature.

Recent reviews describe smell dysfunction across several neurodegenerative conditions and examine how it might contribute to earlier research identification. That makes smell potentially useful as one piece of a wider early-detection puzzle.

But many people with reduced smell will never develop Parkinson’s. Not everyone with Parkinson’s presents identically, and smell alone cannot give an individual probability or diagnosis.

And what about Alzheimer’s disease?

Smell impairment is also observed in mild cognitive impairment, Alzheimer’s disease and other neurodegenerative conditions. Recent reviews suggest that smell identification and discrimination may have potential value in early Alzheimer’s research.

The limitation is crucial: smell impairment cannot reliably distinguish Parkinson’s disease from Alzheimer’s disease, ordinary ageing, nasal disease or other causes.

Fail a smell test ≠ have dementia

Olfactory testing may eventually become part of broader risk assessment. On its own, it cannot reliably tell you why your smell changed, whether you have Parkinson’s or Alzheimer’s disease, or whether you will develop either condition. Context and proper clinical assessment matter.

How is smell actually tested?

Formal olfactory testing can assess different abilities:

Odour identification: can you recognise a smell?
Odour discrimination: can you tell two smells apart?
Odour threshold: how faint can a smell become before you stop detecting it?

Research and clinical settings may use structured tools such as Sniffin’ Sticks or the University of Pennsylvania Smell Identification Test (UPSIT). These are standardised assessments. A random kitchen smell test is not equivalent to a validated clinical assessment.

Why identification is interesting

Identifying a smell requires more than detecting it. The brain must detect the odour, process it, compare it with memory, and attach a name or meaning.

This may help explain why researchers are particularly interested in smell identification and discrimination in cognitive research. It does not prove that a poor identification score identifies one particular disease.

Could we test smell at home?

People can certainly notice changes in familiar smells such as coffee, citrus, herbs, soap or perfume. Noticing change can be useful information to remember and, where appropriate, discuss with a clinician.

But do not turn this into a DIY Parkinson’s or Alzheimer’s screening test. Age Watchers should not tell you to score three out of five smells and calculate your dementia risk.

At-home noticing can help you detect change. It cannot determine the cause.

The Age Watchers baseline idea

One interesting future concept would be to establish a simple baseline of sensory function while someone is well. Not as a diagnostic score, but as a way to notice meaningful change over time.

Potential areas could include smell, hearing, vision, balance, grip strength and walking ability. This fits with the broader idea of intrinsic capacity: the combination of physical and mental abilities that helps a person function.

Age Watchers does not currently provide smell tracking or a smell-based disease screen. Any future sensory baseline would require evidence review, appropriate test design, clinical and safety review, and clear non-diagnostic positioning before implementation.

Do not forget COVID-19

Smell loss became widely recognised during the COVID-19 pandemic. Viral infections can cause substantial smell change, including prolonged loss, parosmia and gradual recovery.

A history of recent infection therefore matters when interpreting a smell change. A post-viral change does not automatically require neurological assessment, although persistent or worrying symptoms should be considered in line with NHS guidance.

When should you speak to your GP?

The NHS advises seeing a GP if your sense of smell does not return to normal in a few weeks. A GP can check for more obvious causes such as sinusitis or nasal polyps and may refer you for specialist tests if needed.

Medical assessment may also be appropriate when a change is persistent, unexplained, progressively worsening or accompanied by other concerning symptoms. For Parkinson’s-specific concerns, use current NHS and Parkinson’s UK advice rather than trying to interpret a smell result alone.

Smell loss can affect nutrition

Reduced smell can make food less enjoyable. In some people, that may contribute to reduced appetite, altered food choices, adding extra salt or sugar to compensate, or weight loss. This can matter particularly for someone already vulnerable to undernutrition.

Smell loss alone does not cause malnutrition in every person. But a persistent change that affects appetite, eating or weight is worth taking seriously and discussing with an appropriate healthcare professional.

And it can affect safety

Someone with significant smell loss may be less able to detect smoke, gas or spoiled food. Smell should never be treated as a substitute for safety equipment.

Keep working smoke alarms in appropriate places.
Use appropriate gas and carbon-monoxide detectors.
Check food dates and storage rather than relying on smell alone.

Can you train your sense of smell?

Olfactory training generally involves repeated exposure to a small set of distinct odours over time. Current evidence suggests it may help some people with post-viral or other forms of smell dysfunction, although response varies and research protocols are not all identical.

Smell training may support recovery of smell function in some conditions. It is not established as a treatment to prevent Parkinson’s disease, Alzheimer’s disease or dementia.

The future: a cheap brain-health signal?

Researchers are interested because MRI, PET scanning and advanced biomarkers can be expensive, invasive or difficult to deploy at population scale. Smell testing can potentially be cheap, quick, non-invasive and repeatable.

The likely future is not:

SMELL TEST → DIAGNOSIS

It is more likely to be a combination of:

SMELL + MOVEMENT + COGNITION + SLEEP + BLOOD OR IMAGING BIOMARKERS + CLINICAL HISTORY

Together, those measures might help build a more complete picture. No single measurement is the whole person.

No single measurement is the whole person.

The Age Watchers framework

MEASURE
Notice meaningful change. A baseline can sometimes be useful, but do not repeatedly test yourself out of anxiety.

UNDERSTAND
Consider the context: recent infection, allergy, sinus problems, medicines, age-related change, or something persistent and unexplained.

IMPROVE
Address treatable causes appropriately. Where relevant, seek medical advice, manage nasal or allergy conditions, and consider clinically appropriate smell training. Do not claim that any of these prevents neurological disease.

MAINTAIN
Protect sensory health and continue noticing meaningful changes without obsessing over them.

MEASURE.
UNDERSTAND.
IMPROVE.
MAINTAIN.

Don’t test your nose. Notice your nose.

Over the next week, simply notice familiar smells:

Morning coffee or tea
Soap or shampoo
Food cooking
Citrus fruit
Herbs and spices

The question is not: “Can I score myself?”

It is: “Has something clearly changed from normal for me?”

If an unexplained change persists for several weeks, follow current NHS guidance.

The useful signal is change — not a homemade diagnosis.

This is why baselines matter

We often only discover that a capability mattered after it has changed: smell, hearing, balance, strength, walking speed or vision.

A baseline gives context. But Age Watchers should only add measurements when they are useful, understandable, evidence-based and actionable. We should not turn every human capability into a score.

The conclusion

Your nose probably is not going to diagnose your future. But it may occasionally tell you that something has changed.

For most people, a change in smell will have an ordinary explanation such as an infection, allergy or nasal problem. For researchers, however, olfactory function is becoming increasingly interesting because changes can occur early in several neurodegenerative diseases.

That makes smell potentially useful. Not magical. Not diagnostic. Useful.

And that is exactly how Age Watchers should think about measurement: measure something because it can tell us something worthwhile, understand its limitations, act when appropriate, and do not turn a number — or a smell — into a verdict.