Most people with Parkinson’s report losing their sense of smell years or even decades prior to diagnosis.
Diminished and loss of sense of smell can impact quality of life affecting taste and, in some cases, leading to weight loss.
Ironically, there has been recent research into the odour people with Parkinson’s have as a potential way to detect the condition.
Smell & Parkinson’s
Many conditions can cause reduced ability to detect odours or complete loss of your sense of smell. This loss could be temporary or lasting. Lasting can be an indicator for brain disease, including a very early symptom of Parkinson’s. However not all people with a reduced sense of smell will go on to develop Parkinson’s.
Scientists do not know why smell loss occurs in Parkinson’s. One popular theory is that the Parkinson’s process may start in gut and the part of the brain controls sense of smell.
What is hyposmia?
Common symptoms that indicate hyposmia include having a hard time identifying smells, not being able to smell as well as you used to, a noticeable reduced sense of taste, and/or nasal congestion and swelling. Anosmia is complete loss of the sense of smell.
Hyposmia is one of the most common and best-characterised conditions that is also one of the first non-motor features of Parkinson’s. The association of hyposmia with Parkinson’s is widely accepted; however the likelihood of developing Parkinson’s is unclear (1).
Most people don’t realise they have a reduced or lost sense of smell (hyposmia or anosmia, respectively) until they are tested. All major brain disorders (e.g. MS, PD, ALS, Alzheimer’s, Huntington’s) are associated with smell loss.
Australian Researchers & Institutions
- Griffith University Researchers at Griffith have studied olfactory dysfunction in Parkinson’s patients using tools like the “Sniffin’ Sticks” test. Their work explores how smell loss varies across individuals and how medications may influence it. In a large multi-centre study investigating the prevalence of olfactory dysfunction in people with Parkinson’s, 400 participants from Australia, Germany, and the Netherlands and used the “Sniffin’ Sticks” test, a validated psychophysical tool, to assess three aspects of smell: threshold, discrimination, and identification.
Key Findings:
- 96.7% of PD patients showed significant smell loss compared to young, healthy individuals.
- When adjusted for age-related norms, 74.5% still showed olfactory dysfunction.
- The breakdown was:
- 45.0% functionally anosmic (complete loss of smell)
- 51.7% hyposmic (reduced sense of smell)
- Only 3.3% normosmic (normal smell function)
- These results support the idea that smell loss is a highly prevalent and reliable early marker of Parkinson’s Disease.
This research adds weight to the theory that Parkinson’s may begin in the olfactory bulb and gut, a concept known as the Braak hypothesis, and highlights the potential of smell testing as a tool for early detection and intervention.
Other causes of smell loss
About half of people over age 60 live with some loss of sense of smell. Parkinson’s is not the only condition that can cause this. Other causes can include:
- COVID-19
- Nasal congestion, cold, allergies, or viral infection
- Head injury
- Aging
- Nasal polyps (growths inside the nose or sinuses)
- Lack of zinc.
Managing loss of sense of smell
Our sense of taste is linked to our sense of smell. Loss or diminished sense of smell may impact quality of life by reducing appetite and lowering our enjoyment of food. You can seek advice about maintaining your enjoyment of foods through varied textures and with a dietictan.
What should I do?
There are not many treatments for lost sense of smell, so take these safety precautions:
- Make sure you have fire alarms and smoke alarms in your home.
- Write dates on leftovers and read best before labels to ensure food safety.
- Consult a dietitian to ensure you are still eating enjoyably and maintaining your optimal nutrition and weight. It’s more about increasing the colours and textures of foods on your plate to stimulate your other senses.
- An ear, nose, and throat specialist (ENT) can do some tests to see how well you can smell. You may need additional tests to rule out other causes of your symptoms.
- If you or someone you know has trouble smelling foods like bananas, dill pickles or liquorice, ask your GP about being assessed for other early Parkinson’s symptoms.
Finding changes in the brain early is really important. It helps scientists learn more about what causes Parkinson’s and how to create better treatments. Some treatments, called neuroprotective strategies, aim to slow down or even stop the condition from getting worse.
To work best, these treatments need to start as early as possible. That’s why a simple and reliable smell test could be a powerful tool… it might help doctors spot Parkinson’s sooner and begin treatment earlier.
Your body odour as an indicator of Parkinson’s
A retired Scottish nurse named Joy Milne noticed her husband’s odour change years prior to his diagnosis. It was only after attending Parkinson’s-related events after his diagnosis that she noticed a similar odour on every person she met with Parkinson’s.
Joy brought this to the attention of researchers who then ‘tested’ her overly sensitive nose and she proved there was something more to this casual observation. See Joy’s TEDx talk here.
People with Parkinson’s often have patches of scaly, red skin on the face and scalp due to over-active glands that secrete an oily, waxy substance called sebum resulting in seborrheic dermatitis.
Diagnosis of Parkinson’s by taking a swab of the extra sebum that produces the odour is being seriously investigated as a non-invasive biomarker, just like high blood pressure can indicate heart problems. (n.b. There are currently no tests that can diagnose Parkinson’s. A collection of your history and clinical examination by a GP, geriatrician, or neurologist. Having a definitive biomarker to objectively make a diagnosis would simplify the process and ensure early and accurate diagnoses for everyone.)
Remember, in order for this biomarker to be useful, it must be able to detect Parkinson’s earlier and more accurately than traditional clinical examination, be an affordable option, is able to be done anywhere, and be easily collected and examined. The good news is current research by a lab in the UK is pointing towards a 3-minute test to examine sebum for certain Parkinson’s biomarkers.
Refer to the Symptoms of Parkinson’s to learn about other symptoms that point towards an early Parkinson’s diagnosis.
Infosheet under review
References:
- Haehner, A., Boesveldt, S., Berendse, H. W., Mackay-Sim, A., Fleischmann, J., Silburn, P. A., Johnston, A. N., Mellick, G. D., Herting, B., Reichmann, H., & Hummel, T. (2009). Prevalence of smell loss in Parkinson’s disease – A multicenter study. Parkinsonism and Related Disorders, 15(7), 490–494.
- Mitchell, E., Mattjie, C., Bestwick, J. P., Barros, R. C., Schuh, A. F., Simonet, C., & Noyce, A. J. (2025). Hyposmia in Parkinson’s disease; exploring selective odour loss. npj Parkinson’s Disease.
- Sui, X., Zhou, C., Li, J., Chen, L., Yang, X., & Li, F. (2019). Hyposmia as a Predictive Marker of Parkinson’s Disease: A Systematic Review and Meta-Analysis. BioMed research international, 2019, 3753786.
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