Skip to content
How It Works
Explore
Resources Ask a Question
Who It's For
Patients Caregivers Providers
Log In Ask a Question
PubMed This is a summary of 21 peer-reviewed journal articles Updated
Neurology

Is Loss of Smell an Early Sign of Parkinson's Disease?

At a Glance

Yes, losing your sense of smell is often one of the very first signs of Parkinson's disease. Known as anosmia, this change can begin a decade or more before movement symptoms like tremors appear. It happens because abnormal proteins often accumulate first in the brain's smell center.

In this answer

4 sections

01

The “Prodromal” Phase of Parkinson’s

02

Why Does Smell Disappear First?

03

Living with Loss of Smell

04

Discussing This With Your Care Team

Yes, losing your sense of smell is often one of the very first signs of Parkinson’s disease. Known medically as anosmia (complete loss of smell) or hyposmia (reduced sense of smell), this change is a well-established early feature of the condition [1][2]. For many people with Parkinson’s, changes in their ability to smell can begin a decade or more before the onset of classic movement-related symptoms like tremors or stiffness [3].

If you lost your sense of smell years ago, you are not alone, and it may well have been the beginning of your Parkinson’s journey.

The “Prodromal” Phase of Parkinson’s

Parkinson’s disease is often thought of as a movement disorder, but the biological changes in the brain actually start long before movement is affected. This early period is called the prodromal phase [4][5]. During this time, the earliest signs of the disease are non-motor symptoms (symptoms that do not affect movement).

Alongside a loss of smell, other common prodromal symptoms include:

  • REM sleep behavior disorder (RBD): Acting out dreams, such as talking, kicking, or punching during sleep [6][5].
  • Chronic constipation: Often occurring years before diagnosis, linked to changes in the gut [7][8].
  • Mood changes: Such as apathy (a lack of motivation or interest), anxiety, or depression [9][10].

The presence of both a reduced sense of smell and REM sleep behavior disorder is a strong indicator of the underlying biological changes associated with Parkinson’s disease [11][12].

Why Does Smell Disappear First?

The reason why smell and sleep are affected so early often comes down to how and where Parkinson’s disease begins in the body. Parkinson’s involves the abnormal clumping of a protein called alpha-synuclein.

According to a leading scientific model known as the Braak hypothesis, in many cases, these protein clumps do not start in the part of the brain that controls movement [13][14]. Instead, pathology often first appears in the peripheral nervous system, specifically in two places:

  1. The olfactory bulb: The part of the brain responsible for processing your sense of smell [13].
  2. The enteric nervous system: The nerves that control your digestive tract, which helps explain early chronic constipation [14][15].

Over many years, the abnormal alpha-synuclein proteins slowly spread upward into the brainstem [13]. When the brainstem is affected, it can cause sleep issues like REM sleep behavior disorder [16][17]. It is only after this slow progression—sometimes taking a decade or more—that the protein clumps reach the substantia nigra, the area of the brain that produces dopamine and controls movement [13][14]. Once this area is damaged, the classic motor symptoms of Parkinson’s finally appear. (Note that research indicates disease progression can vary, and not every patient follows this exact path [14][18]).

Living with Loss of Smell

It is important to know that the sense of smell rarely returns in Parkinson’s disease, and standard dopamine replacement therapies (like levodopa) will not restore it [19]. However, the severity of your smell loss does not predict how severe your movement symptoms will become [19][20].

Because losing your sense of smell removes a critical warning system, you should take practical safety measures:

  • Ensure you have working smoke detectors and carbon monoxide detectors in your home.
  • Rely on visual expiration dates on food rather than the “sniff test.”
  • Consider installing natural gas or propane detectors if your home uses these fuels.

If you also experience REM sleep behavior disorder, creating a safe sleep environment—such as moving nightstands away from the bed or sleeping separately if necessary—can help protect you and your partner from injury.

Discussing This With Your Care Team

If you have been wondering whether your early loss of smell was connected to your Parkinson’s, your instincts were correct. Recognizing this connection validates what many patients feel: that something was changing in their body long before their formal diagnosis.

While there are no treatments to bring your smell back, discussing these early symptoms with your neurologist remains valuable. Because smell loss and sleep disorders are linked to how the disease spreads, this information helps your doctor anticipate other non-motor symptoms, such as cognitive changes or blood pressure drops, and screen for them proactively [19][21].

Common questions in this guide

Why do people with Parkinson's lose their sense of smell?
Parkinson's involves the abnormal clumping of a protein called alpha-synuclein. These clumps often first appear in the olfactory bulb, the part of the brain responsible for processing your sense of smell, long before movement is affected.
How long before a Parkinson's diagnosis does loss of smell start?
Changes in the ability to smell can begin a decade or more before the onset of classic movement-related symptoms like tremors or stiffness. This early period is known as the prodromal phase.
Will my sense of smell return with Parkinson's treatment?
No, the sense of smell rarely returns in Parkinson's disease. Standard dopamine replacement therapies, such as levodopa, do not restore a lost sense of smell.
What other early non-motor symptoms should I watch for in Parkinson's?
Other common early symptoms include chronic constipation, mood changes like anxiety or apathy, and REM sleep behavior disorder, which involves acting out dreams by talking, kicking, or punching during sleep.
How can I stay safe at home with a loss of smell?
Because losing your sense of smell removes a critical warning system, you should install working smoke, carbon monoxide, and natural gas detectors. Rely on visual expiration dates on food instead of trying to smell if it has gone bad.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Given my early non-motor symptoms like smell loss or sleep changes, are there specific cognitive or autonomic issues we should be actively screening for?
  2. 2.How frequently should we monitor my other non-motor symptoms, and what early signs should I report to you?
  3. 3.Could any of my current medications be making my sleep disturbances or other non-motor symptoms worse?
  4. 4.Are there specific safety protocols or evaluations you recommend for managing my REM sleep behavior disorder?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

Related questions

What Are the Benefits of Boxing for Parkinson's Disease?Do All Parkinson's Patients Need a Wheelchair?Does Deep Brain Stimulation Slow Parkinson's Progression?Does Parkinson's Disease Affect Life Expectancy?Can I Get Focused Ultrasound Instead of DBS for Parkinson's?How Is Parkinson's Diagnosed vs. Essential Tremor?How Long Is the Parkinson's Disease Honeymoon Period?How to Take Levodopa with Protein Meals for Parkinson'sParkinson's Speech Therapy: Does It Help Hypophonia?Is Parkinson's Disease Genetic or Hereditary?Do I Need a Movement Disorder Specialist for Parkinson's?Do Parkinson's Drugs Cause Impulse Control Disorders?Parkinson's Tremor vs Dyskinesia: What's the Difference?How Can You Sleep Safely with REM Sleep Behavior Disorder?What Causes Dizziness in Parkinson's Disease?Why Does Parkinson's Medication Wear Off?Tremor Dominant Parkinson's: How Fast Does It Progress?

References

References (21)
  1. 1

    Sweet or Bland Dreams? Taste Loss in Isolated REM-Sleep Behavior Disorder and Parkinson's Disease.

    Nigam M, Ayadi I, Noiray C, et al.

    Movement disorders : official journal of the Movement Disorder Society 2021; (36(10)):2431-2435 doi:10.1002/mds.28692.

    PMID: 34117799
  2. 2

    Olfactory loss and aging: connections with health and well-being.

    Papazian EJ, Pinto JM

    Chemical senses 2021; (46()) doi:10.1093/chemse/bjab045.

    PMID: 34673938
  3. 3

    Dopaminergic neurodegeneration in the substantia nigra is associated with olfactory dysfunction in mice models of Parkinson's disease.

    Yuan Y, Ma X, Mi X, et al.

    Cell death discovery 2023; (9(1)):388 doi:10.1038/s41420-023-01684-8.

    PMID: 37865662
  4. 4

    REM Sleep Behavior Disorder in Parkinson's Disease and Other Synucleinopathies.

    St Louis EK, Boeve AR, Boeve BF

    Movement disorders : official journal of the Movement Disorder Society 2017; (32(5)):645-658 doi:10.1002/mds.27018.

    PMID: 28513079
  5. 5

    Alterations of Peripheral Lymphocyte Subsets in Isolated Rapid Eye Movement Sleep Behavior Disorder.

    Zheng Y, Li Y, Cai H, et al.

    Movement disorders : official journal of the Movement Disorder Society 2024; (39(7)):1179-1189 doi:10.1002/mds.29798.

    PMID: 38529776
  6. 6

    REM sleep, REM parasomnias, REM sleep behaviour disorder.

    Szûcs A, Mutti C, Papp A, et al.

    Ideggyogyaszati szemle 2022; (75(5-06)):171-182 doi:10.18071/isz.75.0171.

    PMID: 35819343
  7. 7

    Gut brain axis: an insight into microbiota role in Parkinson's disease.

    Moustafa SA, Mohamed S, Dawood A, et al.

    Metabolic brain disease 2021; (36(7)):1545-1557 doi:10.1007/s11011-021-00808-2.

    PMID: 34370175
  8. 8

    Relationships Between Rapid Eye Movement Sleep Behavior Disorder and Parkinson's Disease: Indication from Gut Microbiota Alterations.

    Zhang P, Huang P, Li Y, et al.

    Aging and disease 2024; (15(1)):357-368 doi:10.14336/AD.2023.0518.

    PMID: 37307829
  9. 9

    The activities of daily living partially mediate the relationship between rapid eye movement sleep behavior disorder and depressive symptoms in Parkinson's disease.

    Wang Q, Zheng S, Jing B, et al.

    Frontiers in neurology 2024; (15()):1357721 doi:10.3389/fneur.2024.1357721.

    PMID: 39131055
  10. 10

    Assessing prevalence and risk factors for REM sleep behavior disorder among patients with inflammatory bowel disease.

    Reddy VL, Chen Z, Dewain S, et al.

    NPJ Parkinson's disease 2025; (11(1)):282 doi:10.1038/s41531-025-01051-7.

    PMID: 41034267
  11. 11

    Inaccurate self-report of olfactory dysfunction in REM Sleep Behaviour Disorder and implications for prognosis.

    Roguski A, Rolinski M, Jones MW, Whone A

    Clinical parkinsonism & related disorders 2023; (8()):100176 doi:10.1016/j.prdoa.2022.100176.

    PMID: 36594073
  12. 12

    The combined effect of REM sleep behavior disorder and hyposmia on cognition and motor phenotype in Parkinson's disease.

    Kang SH, Lee HM, Seo WK, et al.

    Journal of the neurological sciences 2016; (368()):374-8.

    PMID: 27538667
  13. 13

    Alpha-synuclein: prion or prion-like?

    Leak RK, Frosch MP, Beach TG, Halliday GM

    Acta neuropathologica 2019; (138(4)):509-514 doi:10.1007/s00401-019-02057-1.

    PMID: 31407028
  14. 14

    Neuropathology of α-synuclein in Parkinson's disease.

    Choong CJ, Mochizuki H

    Neuropathology : official journal of the Japanese Society of Neuropathology 2022; (42(2)):93-103 doi:10.1111/neup.12812.

    PMID: 35362115
  15. 15

    Lots of Movement in Gut and Parkinson's Research.

    Mercado G, Brundin P

    Trends in endocrinology and metabolism: TEM 2019; (30(10)):687-689 doi:10.1016/j.tem.2019.08.001.

    PMID: 31473011
  16. 16

    Diagnostic REM sleep muscle activity thresholds in patients with idiopathic REM sleep behavior disorder with and without obstructive sleep apnea.

    McCarter SJ, St Louis EK, Sandness DJ, et al.

    Sleep medicine 2017; (33()):23-29 doi:10.1016/j.sleep.2016.03.013.

    PMID: 28449901
  17. 17

    Propagated α-synucleinopathy recapitulates REM sleep behaviour disorder followed by parkinsonian phenotypes in mice.

    Shen Y, Yu WB, Shen B, et al.

    Brain : a journal of neurology 2020; (143(11)):3374-3392 doi:10.1093/brain/awaa283.

    PMID: 33170925
  18. 18

    The α-Synuclein Origin and Connectome Model (SOC Model) of Parkinson's Disease: Explaining Motor Asymmetry, Non-Motor Phenotypes, and Cognitive Decline.

    Borghammer P

    Journal of Parkinson's disease 2021; (11(2)):455-474 doi:10.3233/JPD-202481.

    PMID: 33682732
  19. 19

    Evaluation of Olfactory Function by Iranian Smell Diagnostic Test in Patients with Parkinson's disease in North of Iran.

    Kiakojuri K, Pouladi L, Saadat P, et al.

    Iranian journal of otorhinolaryngology 2021; (33(118)):271-279 doi:10.22038/ijorl.2021.50564.2688.

    PMID: 34692574
  20. 20

    Association between Olfactory Deficit and Motor and Cognitive Function in Parkinson's Disease.

    Yoo HS, Chung SJ, Lee YH, et al.

    Journal of movement disorders 2020; (13(2)):133-141 doi:10.14802/jmd.19082.

    PMID: 32241078
  21. 21

    The Association of Olfactory Dysfunction With Depression, Cognition, and Disease Severity in Parkinson's Disease.

    Fang TC, Chang MH, Yang CP, et al.

    Frontiers in neurology 2021; (12()):779712 doi:10.3389/fneur.2021.779712.

    PMID: 34880827

This page explains the connection between loss of smell and Parkinson's disease for educational purposes only. Always consult your neurologist for medical advice and symptom management.

Get notified when new evidence is published on Parkinson's Disease.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.