Parkinson's disease cases have risen dramatically in the U.S. over the past decade and a carcinogen widely found in household and industrial cleaning products may be to blame.
Most Parkinson's disease cases are idiopathic - which means they have no known cause. However, researchers are increasingly convinced environmental exposure to trichloroethylene, a chemical compound used in industrial degreasing, dry-cleaning and household items such as certain shoe polishes and carpet cleaners, is a factor.
Trichloroethylene was first linked to Parkinson's disease in 2012 but the compound is often ignored in research because, in some cases, decades can pass between exposure and the onset of symptoms, according to The Guardian.
Trichloroethylene is banned in Europe but there are no federal restrictions in the U.S. - despite a growing body of evidence pointing to restrictions in the country. Minnesota and New York only have prohibited the compound.
As a result, trichloroethylene is surprisingly prevalent in water Americans drink and bathe in. It has been discovered in approximately 30% of the country's groundwater - though experts say the true figure is likely higher.
Regardless of the exact percentage, University of Rochester Medical Center neurologist Ray Dorsey said widespread contamination might explain the increasing number of Parkinson's disease cases - which might double in just another 25 years.
The clearest evidence of the danger of trichloroethylene to humans comes from employees exposed to the chemical. Trichloroethylene was discovered to be "a risk factor for parkinsonism" in a 2008 peer-reviewed study published in the Annals of Neurology. A 2011 study found "a sixfold increase in the risk of developing Parkinson's in individuals exposed in the workplace."
Trichloroethylene has been linked to cancers of the cervix, liver, biliary passages, lymphatic system and male breast tissue, as well as fetal heart defects. Its recognized link to Parkinson's disease is often overlooked since trichloroethylene exposure can predate the disease's onset by decades.
While some people become ill quickly after being exposed to trichloroethylene, others may unknowingly work or live on contaminated sites for the majority of their lives before developing Parkinson's symptoms.