Smell and Taste Loss in Parkinson’s

Loss of smell and taste are a deeply impactful aspect of Parkinson’s disease (PD), often emerging years before more visible, classic PD symptoms appear. These subtle sensory changes can go unnoticed or be dismissed entirely, yet growing research suggests they may offer valuable clues about the earliest stages of the disease. Understanding how and why smell and taste are affected in Parkinson’s not only helps paint a fuller picture of the illness, but also opens the door to earlier detection and, potentially, intervention. While there is still much to learn, there are some strategies that may help people with PD manage these sensory changes and improve their quality of life.

What is Loss of Smell and Taste?

Smell and taste, while being two different senses, are closely connected. When we chew food in our mouths, odour molecules draft backwards into the nose through a process called retronasal olfaction. Our tongues tell us if something is sweet or salty, but our nose helps differentiate precisely what it is we are eating – is the sweetness a grape or an apple? This is why the loss of smell can lead people to believe their sense of taste is also gone, even if it itself is not reduced (Bonvissuto, 2024). 

Loss of smell and taste, known medically as hyposmia and ageusia, can occur as a result of various conditions, and often present slowly. While some individuals lose their sense of smell and taste entirely, others experience only a partial loss, detecting certain odors or flavours but not others. However, not all changes in smell and taste result in the loss of the senses – some people experience distortions, known as parosmia or dysgeusia, where things smell or taste different than they should – for example, a normally pleasant odour, like coffee, can smell rotten or chemical-like (Johns Hopkins Medicine, n.d.). In general, loss of smell can occur due to blocked airflow to the odour-detecting nerves, damage to those nerves themselves, or injury to the brain regions responsible for processing smell (Mass Eye and Ear, n.d.).

How They Relate to Parkinson’s

Loss of smell may be one of the earliest signs of Parkinson’s disease, predating the diagnosis by several years in many instances. The very first double-blind, controlled study on the topic took place in Minnesota in 1975 by two researchers named Ansari and Johnson. They were the first to show that people with PD had significantly reduced smell acuity (the ability to detect and distinguish between odours), when compared to age and sex matched control groups (Ansari & Johnson, 1975). 

More recently, a study followed 474 people with idiopathic (meaning the cause was unknown) smell loss for 15 years and found that nearly 10% went on to be diagnosed with PD, about 11 years after the smell problems began. However, 29% of those with both smell and taste loss developed Parkinson’s (Haehner et al., 2018). The American Academy of Family Physicians (AAFP) looked at the findings from multiple large cohorts and clinical studies on the topic and found that up to 90% of people with PD presented with smell loss in the early to moderate stages of the illness (Malaty & Malaty, 2013).

Neurological Changes in PD

The link between the loss of smell and Parkinson’s was not always understood. Scientists now believe that the disease may actually begin in parts of the brain involved in smell, specifically the olfactory bulb and lower brainstem, before it spreads to other areas. Changes linked to PD are also found in several other parts of the brain that help process smell. These include regions involved in recognizing and reacting to different scents, such as the amygdala (which also handles emotions), and parts of the brain that connect memory and decision-making with smell. One of these areas, called the anterior olfactory nucleus (AON), is located near the olfactory bulb and shows damage in people with Parkinson’s, which is tied to loss of nerve cells there (Fullard et al., 2017).

A Biomarker for PD

In fact, the loss of smell is such a significant symptom that researchers are now using it as a biomarker to identify individuals at high risk of developing Parkinson’s, even before they develop other symptoms. The Parkinson Associated Risk Syndrome study (PARS), published in 2017, looked at whether smell identification testing, followed by a special brain scan called dopamine transporter imaging (DaTscan), a type of scan that shows the dopamine system in the brain, can help correctly identify those at highest risk of Parkinson’s. 

The researchers mailed smell tests to people in the community and then invited those with a reduced sense of smell for a DaTscan. They followed up annually for four years to see if anyone developed Parkinson’s. Of the individuals who had both a loss of sense of smell and low dopamine on the DaTscan, 67% developed PD within the four-year study period (Jennings et al., 2017). 

Unfortunately, as of now, there are no disease-modifying therapies for Parkinson’s, but scientists hope that breakthroughs are on the horizon. When such therapies emerge, the screening approaches like the one demonstrated in the PARS study will be critical – they offer a way to identify individuals in the earliest, pre-motor stages of the disease, opening the door to early intervention with neuroprotective treatments. Perhaps one day science will be so advanced as to prevent the onset of motor symptoms entirely – but that won’t be possible unless we can identify those at risk before the symptoms appear (Jennings et al., 2017).

Strategies to Improve Quality of Life

Losing one’s sense of smell and taste can be very difficult, both emotionally and practically. So many pleasurable activities in life – from sharing a delicious meal with loved ones, to enjoying the smell of fresh, spring flowers – are dependent on our sense of smell. Not surprisingly, studies find that those with smell loss are more likely to suffer from mental health conditions, such as anxiety and depression (Marin et al., 2023). 

Fortunately, there are ways to improve quality of life with smell and taste loss. Some strategies include:

• Safety first – always: Because our sense of smell and taste provide information about the world around us, individuals with this sensory loss are at greater risk from environmental hazards, such as fires, gas leaks, and spoiled foods. Always make sure your smoke detectors are regularly checked, keep a functioning carbon monoxide detector in the home if you use natural gas, and pay close attention to expiry dates on food. If you have loved ones who live with you, enlist their help in meal preparation.
• Smell retraining: One way to improve your smell may be to train the parts of the brain responsible for the sense through smell retraining. This usually involves regularly sniffing a range of scent-producing items (for example, citrus fruits, eucalyptus, peanut butter, etc) while remembering times in the past you have smelled the item, which will help trigger odour particle recognition in the brain. Try to do this once or twice a day, sniffing each scent for 30 seconds to two minutes, for four weeks. Affordable smell retraining kits are available through many retailers (Godman, 2023).
• Ensure a healthy diet despite appetite reduction: While no diet has been proven to bring back a diminished or lost sense of smell, a healthy diet is vital for overall health and wellbeing. Understandably, not being able to smell and taste your food may lead to lower appetite and intake. If you need help with dietary concerns, seek the advice of a registered dietician. The BC Brain Wellness Program offers several resources at https://www.bcbrainwellness.ca/resources/nutrition-resources
• Ask your doctor about medication: While there are no pharmacological treatments for smell loss in PD, in one study of 224 people with Parkinson’s, those taking the medication rasagiline for less than eight years had better odour discrimination compared to those not taking it. However, this benefit did not persist in those with longer disease duration. The results suggest rasagiline may help with smell function in the early stages of Parkinson’s. Always be sure to discuss what medications are right for you with your healthcare team (Haehner et al., 2015).
• Take care of your mental health: The sense of smell might not seem that important to individuals who have never experienced losing it. In fact, one shocking study surveyed 407 participants (college students and adults), asking them to compare the value of smell, hearing, and vision against each other and against common items like phones, pets, and money. Results showed that smell was consistently rated as the least valuable sense, with many participants willing to give it up in exchange for everyday items (for example, to be able to keep their phone) (Herz & Bajec, 2022). However, people who have experienced smell loss know firsthand the devastating impact it can have on daily life and enjoyment, which is why caring for one’s mental health is so important. Parkinson Society BC offers free clinical counselling for those touched by PD, offering a safe space to process difficult emotions. Learn more at https://parkinson.bc.ca/resources-support/services/counselling-healthcare-navigation

Sources

Ansari, K. A., & Johnson, A. J. (1975). Olfactory function in patients with Parkinson’s disease. Journal of Chronic Diseases, 28(9), 493–497. 

Bonvissuto (2024). What’s Causing My Loss of Smell and Taste? https://www.webmd.com/brain/ss/slideshow-causes-of-loss-of-smell-and-taste 

Fullard, M. E., Morley, J. F., & Duda, J. E. (2017). Olfactory dysfunction as an early biomarker in Parkinson’s disease. Neuroscience Bulletin, 33(5), 515–525. https://doi.org/10.1007/s12264-017-0170-x 

Godman, H. (2023). Ways to regain your sense of smell. https://www.health.harvard.edu/diseases-and-conditions/ways-to-regain-your-sense-of-smell 

Haehner, A., Habersack, A., Wienecke, M., Storch, A., Reichmann, H., & Hummel, T. (2015). Early Parkinson’s disease patients on rasagiline present with better odor discrimination. Journal of Neural Transmission, 122(11), 1541–1546. https://doi.org/10.1007/s00702-015-1397-9 

Haehner, A., Masala, C., Walter, S., Reichmann, H., & Hummel, T. (2019). Incidence of Parkinson’s disease in a large patient cohort with idiopathic smell and taste loss. Journal of Neurology, 266(2), 339–345. https://doi.org/10.1007/s00415-018-9141-3 

Herz, R. S., & Bajec, M. R. (2022). Your money or your sense of smell? A comparative analysis of the sensory and psychological value of olfaction. Brain Sciences, 12(3), 299. https://doi.org/10.3390/brainsci12030299 

Jennings, D., Siderowf, A., Stern, M., Seibyl, J., Eberly, S., Oakes, D., & Marek, K. (2017). Conversion to Parkinson disease in the PARS hyposmic and dopamine transporter–deficit prodromal cohort. JAMA Neurology, 74(8), 933–940. https://doi.org/10.1001/jamaneurol.2017.0985 

Johns Hopkins Medicine (n.d.). Smell and Taste Disorders. https://www.hopkinsmedicine.org/health/conditions-and-diseases/smell-and-taste-disorders 

Malaty, J., & Malaty, I. A. C. (2013). Smell and taste disorders in primary care. American Family Physician, 88(12), 852–859. 

Marin, C., Alobid, I., Fuentes, M., López-Chacón, M., & Mullol, J. (2023). Olfactory dysfunction in mental illness. Current Allergy and Asthma Reports, 23(3), 153–164. https://doi.org/10.1007/s11882-023-01068-z 

Mass Eye and Ear (n.d.). Smell and Taste Loss. https://masseyeandear.org/conditions/smell-taste-loss 

This content was published in the Fall 2025 edition of our quarterly magazine, Viewpoints. The content was accurate as of this publication date.