Parkinson’s Disease (PD) is a progressive neurodegenerative condition that primarily affects motor function, but it also causes a range of non-motor symptoms. One unexpected discovery is that people with PD emit a subtle, yet distinct, odor. Scientific investigation has validated the existence of this signature scent, confirming it is directly related to the disease process and is measurable through chemical analysis. This finding has opened a new avenue of research focused on creating a non-invasive test for earlier diagnosis.
How the Parkinson’s Odor Was Identified
The initial discovery of the Parkinson’s odor began as an anecdotal observation by an individual with hyperosmia, a condition that grants a heightened sense of smell. Joy Milne first noticed a subtle change in her husband’s scent years before his Parkinson’s diagnosis, describing it as a musky or musty aroma. She later realized the scent was shared by others with the condition when attending a support group meeting.
This observation led to a collaboration with scientists to validate her ability. In a pioneering study, she smelled T-shirts worn by individuals with and without PD, successfully identifying nearly all the shirts from the Parkinson’s group. Crucially, she also incorrectly identified one control subject’s shirt as having the scent; that individual was diagnosed with the disease eight months later, confirming the odor existed long before a clinical diagnosis. Researchers confirmed the odor was present in sebum, the waxy substance on the skin, leading them to focus on collecting skin swabs from the upper back for chemical analysis.
The Biological Source of the Scent
The distinctive scent associated with Parkinson’s disease originates from changes in the chemical composition of sebum, the oily, waxy substance secreted by the sebaceous glands. Sebum contains a complex mixture of lipids and is often produced in greater quantities in PD patients, a non-motor symptom known as seborrhea. The disease process appears to alter the body’s metabolism, leading to a modified chemical signature within this skin oil.
The Parkinson’s odor is caused by an alteration in the levels of Volatile Organic Compounds (VOCs) within the sebum. VOCs are organic chemicals that easily vaporize at room temperature, making them detectable as scents. Using mass spectrometry, scientists identified a distinct “volatilome,” or profile of volatile compounds, specific to PD patients.
Compounds such as eicosane, octadecanal, and certain hippuric acid derivatives are elevated in the sebum of those with Parkinson’s. Conversely, the concentration of perillic aldehyde was found to be reduced. These alterations in the balance of various compounds are believed to be a consequence of the disease, potentially linked to the accumulation of alpha-synuclein—a molecular hallmark of PD—in the skin, or a change in the skin’s microflora. The combination of these specific elevated and reduced VOCs creates the musky scent.
Translating Scent Detection into Medical Tools
The identification of a specific chemical signature for Parkinson’s disease has created a pathway for developing a non-invasive diagnostic test. Current diagnosis relies on observing motor symptoms, meaning the disease is often advanced when identified. A simple test based on the odor profile could allow for much earlier detection, potentially before the onset of motor symptoms.
The primary method involves analyzing a skin swab sample taken from the upper back, an area rich in sebum. This sample is analyzed using sophisticated laboratory instruments like gas chromatography-mass spectrometry (GC-MS). GC-MS separates and identifies the individual VOCs to determine if the Parkinson’s signature is present, identifying the disease with a high degree of accuracy in a laboratory setting.
To make this technology practical for widespread clinical use, researchers are developing portable devices known as “electronic noses,” or e-noses. These devices combine smaller, more rapid gas chromatography systems with specialized sensors and machine learning algorithms. The e-noses are trained to recognize the precise pattern of VOCs that constitute the PD odor profile, offering a fast and relatively inexpensive diagnostic tool. While early prototypes show promise, further testing on larger and more diverse populations is necessary to increase accuracy and specificity before these devices can be implemented.