The test could help doctors diagnose patients sooner and identify those in the earliest stages of the disease who may benefit from experimental drugs aiming to protect brain cells from being killed off.
Perdita Barran, at the University of Manchester, said the test had the potential to significantly reduce the time taken to distinguish people with normal brain ageing from those with the first signs of the disorder.
The study was inspired by Joy Milne, a 68-year-old retired nurse from Perth.
Most people cannot detect the scent of Parkinson's, but some with a heightened sense of smell report a musky odour.
Joy, noticed the smell on her husband, Les, 12 years before he was diagnosed and realised she could sniff out Parkinson's when she attended a patient support group and found they all smelled the same.
She mentioned the odour to Tilo Kunath, a neurobiologist who studies Parkinson's at Edinburgh University. Kunath tested Joy's skills by having her sniff T-shirts that had been worn by healthy people or Parkinson's patients.
Joy identified all those worn by the patients and said one more bore the same scent. Eight months later, the wearer was diagnosed with the disease.
READ MORE: Woman who can ‘sniff out’ Parkinson’s helps expertsFor the latest study, Barran worked with Kunath and Joy to identify the main substances that give rise to the Parkinson's odour. They focused on compounds in sebum, a waxy fluid secreted in the skin. The scientists used mass spectrometry to measure levels of volatile chemicals in sebum on swabs from Parkinson's patients and healthy volunteers, and whittled down the fragrant compounds from thousands to just four that appear most important for the scent.
Writing in the journal ACS Central Science, the researchers describe how Joy who has worked with the University of Manchester on research for three years, confirmed that mixtures of the four compounds had the same musky smell as Parkinson's patients.
Tests found that levels of three substances, eicosane, hippuric acid and octadecanal, were all higher than normal in the sebum of Parkinson's patients, while levels of a fourth substance, perillic aldehyde, were lower.
To see whether the test can spot Parkinson's before doctors can, the scientists have teamed up with researchers in Austria who study people with REM sleep disorders. Those affected have a 75 per cent risk of developing Parkinson's or a similar disease in later life.
"If we can detect the disease early on, that would be very good news. It would mean we have a test that picks it up before motor symptoms appear," Barran said.
READ MORE: Health service struggling to meet Scottish Parkinson’s needsIn parallel, more than 1,000 Parkinson's patients and hundreds of healthy people will have their sebum analysed to see how reliable the test is. Scientists will also look at whether changes in the odour reflect the progression of the disease, or even different forms of Parkinson's.
Werner Poewe, director of neurology at the Medical University of Innsbruck, said diagnosing Parkinson's early was "critical" to give patients the best advice and treatment to delay the onset of the illness. Milne's next collaboration with the Manchester group will aim will to identify chemicals that produce a signature odour for tuberculosis.