French scientists say they have proof that dogs can pick up the smell of an epileptic seizure.
The University of Rennes team hope the findings could lead to ways to predict when people will have a seizure.
These could include dogs or "electronic noses" that pick up the precise odour being given off during a seizure.
Dogs have previously been shown to be able to sniff out diseases including cancers, Parkinson's, malaria and diabetes.
- Epilepsy is caused by disruption to the electrical signals in the brain causing seizures
- The disease can run in families or be caused by a stroke or oxygen deprivation at birth
Some people with epilepsy already rely on the animals.
One sleeping in a child's bedroom can alert family members of a seizure in the middle of the night.
The latest study, in the journal Scientific Reports, trained five dogs from Medical Mutts, in the US, to recognise the smell of sweat taken from a patient having a seizure.
They were then given a choice of seven sweat samples taken from other patients while they were either relaxing, exercising or having a seizure.
Two of the dogs found the seizure sample about two-thirds of the time and the other three were 100% accurate
The report says: "The results are extremely clear and constitute a first step towards identifying a seizure-specific odour."
That would require detailed chemical analysis to identify the specific compounds involved.
It is also unknown how an epileptic seizure leads to a change in smell.
Dr Amelie Catala, from the University of Rennes, told BBC News: "Further research is needed but it is possible that the change in electrical activity triggers the releasing of some neurohormones that will in the end trigger the scent or that it is linked to stress-related molecules and pathways, or anything else - all hypothesis are still to be considered."
But the researchers hope the field could eventually help patients.
"It could lead to significant improvements in terms of seizure detection or prediction systems," the report adds.
And that could give time for someone to call for help or get themselves somewhere safe before their seizure begins.
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