For the first time, researchers have shown that dogs can identify the unique odor of a seizure. In the future, this new understanding could help design ways to halt seizures before they happen.

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The researchers behind a new study conclude that body seizures produce an odor that dogs can detect.

In past studies, researchers have had varying levels of success in training dogs to detect diabetes, malaria, certain types of cancer, and some kidney diseases.

One particularly impressive study found that dogs could detect colon cancer from breath samples in 91 percent of cases.

There is even some evidence that canines can spot migraines before they begin.

Although scientists have made headway with the canine detection of some ailments, they have not investigated whether dogs can sniff out epilepsy-related seizures.

It is likely that this is due to the number of confounding factors. For instance, epilepsy can arise because of head injury, genetic factors, tumors, or stroke, and it often occurs alongside other conditions, such as anxiety disorders or depression.

As the authors of the current study write, “This high variability may explain why no study has been undertaken on a potential seizure-specific odor yet.”

However, if a dog could detect the early signs of a seizure before it began, this could be of real benefit to the 3 million adults in the United States with epilepsy. Having warning of the seizure would allow them to seek a safer environment before it began.

Although there is anecdotal evidence that some dogs can predict seizures in their owners, it is not clear what cues the dogs are using. For instance, they might be basing their prediction on subtle changes in the way that their owner is behaving.

Recently, a group of researchers from the University of Rennes in France ran a small study to identify whether dogs could use olfactory clues to detect seizures. They recently published their findings in the journal Scientific Reports.

The researchers collected breath and sweat samples from five people with epilepsy. All of the participants had different forms of the condition, which included frontal lobe complex partial seizures and temporal lobe complex partial seizures.

The sample included three people whose condition developed due to cerebral malformation and two whose epilepsy had genetic origins.

The scientists took three types of odor sample from each participant, collecting one type during a seizure, another while the participant was resting, and a third during exercise. They included the exercise sample to ensure that any response from the dogs was not solely due to a general increase in sweating.

The scientists enlisted five dogs that had already received training to identify a range of diseases and disorders and had learned to approach and stand above a target odor. The dogs were all different breeds, and they included a golden-labrador retriever mix, a border collie mix, and a Chesapeake Bay retriever mix.

During each trial, the scientists presented the dog with seven samples from the same participant. They used four from a time when the participant was not experiencing a seizure, two from a period of exercise, and one from during a seizure.

Impressively, each of the five dogs correctly identified the seizure sample in all of the trials, taking an average of less than 8 seconds per trial. The authors conclude:

This clearly demonstrates for the first time that there is indeed a seizure-specific odor across individuals and types of seizures.”

As the study only included a handful of participants and dogs, scientists will need to replicate the results in a more extensive study. However, as the researchers write in their paper, although the sample size is small, “the results are extremely clear and constitute a first step toward identifying a seizure-specific odor.”

It is also worth noting that the researchers used body fluids that they had collected during a seizure, so they cannot yet conclude that the dogs would be able to predict a seizure before its onset.

Despite the trial’s small size, the findings lay the groundwork for more research in the future. One of the next steps will be to identify the exact chemicals that define the odor of a seizure.

Once scientists have pinned down the specific chemical signature, it might be possible to design devices that can detect it and, eventually, find a way to predict seizures before they occur.

Overall, the authors believe that their study “reopens the possibility that seizures may be anticipated by looking further at olfactory characteristics. […] Dogs demonstrate that there is hope in this direction.”