Earwax named as a factor indicating a dangerous disease

Researchers in China have identified key differences in the composition of earwax in people with Parkinson's disease compared with those without the condition, suggesting the sticky material in the ears contains secretions that may indicate a person's risk of developing the disease.

Scientists from Zhejiang University took earwax samples from 100 people with Parkinson's disease and 79 without it. They chose earwax because much of it is made up of sebum, an oily substance that undergoes chemical changes in Parkinson's disease and releases various volatile organic compounds (VOCs), the Daily Mail reports.

Parkinson's disease causes neurodegeneration, inflammation and oxidative stress, changing the composition of sebum and creating a distinct odor, the publication notes. The disease also causes gradual brain damage, causing tremors, stiffness and slow movement. Symptoms worsen over time and include sudden freezing, loss of speech, trouble swallowing that often leads to pneumonia, and falls, which are common causes of death among people with Parkinson's.

Four specific types of VOCs were identified among people with the disease, suggesting that earwax could potentially be a readily available indicator of Parkinson's disease that could allow patients to avoid invasive diagnostic tests and spinal taps.

The disease currently affects around 10 million people worldwide, with nearly 90,000 new cases diagnosed each year, the Daily Mail notes. With that number predicted to rise, early diagnosis is more important than ever. While there is no cure, medication can be started early to manage symptoms and slow the progression of the disease.

The researchers fed VOC data from earwax samples into an algorithm that accurately identified patients' Parkinson's disease status 94 percent of the time, demonstrating the potential for a rapid and reliable diagnostic tool.

All of the VOCs that the researchers isolated were significant in differentiating people with the disease from those without, even after accounting for age and lifestyle factors. Two VOCs, ethylbenzene and 4-ethyltoluene, are compounds commonly found in plastics and petroleum products. Their presence indicates inflammation in the brain, which is a key driver of the breakdown of dopamine in the brain. Dopamine, often considered the “feel-good” neurotransmitter, is a key chemical that regulates movement control. As dopamine levels drop as Parkinson’s disease progresses, people become increasingly immobile.

Another important component of VOC is pentanal, which is formed during the breakdown of fats. Elevated dopamine levels indicate cellular damage, a hallmark of Parkinson's disease. This compound has been linked to the accumulation of protein clumps in patients' brains. And the presence of VOC-2-pentadecyl-1,3-dioxolane likely reflects problems with fat metabolism that may have arisen as a result of changes in the patients' skin microbiome.

It’s unclear whether these VOCs have any direct connection to Parkinson’s disease, but there is a growing body of research pointing to a link between PD and an imbalance in the gut microbiome. Research suggests that VOCs are produced by an imbalance of beneficial bacteria in the gut, which are also linked to brain health.

An imbalance that allows harmful bacteria to proliferate leads to the spread of toxins that can cause inflammation in the brain. VOCs come from a wide range of toxic sources in the environment: from pesticides used to grow food, industrial chemicals found in gasoline, and solvents found in everyday items like dry cleaning chemicals and adhesives, to cleaning products, car exhaust, and contaminated groundwater.

Parkinson's disease is thought to be caused by a combination of genetic and environmental factors. It is the fastest growing brain disorder in the world, and "the leading cause is exposure to environmental toxicants," according to research from the National Institutes of Health.

In the U.S. alone, deaths from Parkinson's disease have more than doubled in the past 20 years, with nearly 35,000 deaths in 2019, up from 14,500 in 1999. While the study that earwax can provide clues about the development of Parkinson's disease is new, the study of the role of VOCs in the process is not.

A large meta-analysis conducted in 2023 found that VOCs are present in the breath and sebum of people with the disease compared to those without it. These compounds are directly linked to oxidative stress, or the barrage of damage that cells undergo before they die.