Diabetes alert dogs are some of the unsung heroes of the medical world: They enthusiastically work for free (or, rather, for treats), and they’re miraculously able to sniff out low blood sugar, helping diabetics anticipate hypoglycemia attacks. But while helper dogs have long been an important resource for diabetics, scientists have never understood exactly how they were able to detect the onset of hypoglycemia—until now. 

Gizmodo reports that a group of scientists at the Wellcome Trust-MRC Institute of Metabolic Science and the University of Cambridge may have identified the chemical that alerts dogs of oncoming hypoglycemia attacks. In a recent study published in Diabetes Care, researchers studied the chemicals present in the exhaled breath of eight diabetic women. They analyzed the chemical make-up of the subjects’ breath when blood sugar was normal, then carefully lowered their blood sugar and studied their breath during hypoglycemia. They found that isoprene, an organic compound commonly found in human breath (and tree emissions), increased sharply during hypoglycemic episodes.

Researchers now believe that isoprene may be one of the chemicals dogs detect when their owners are experiencing low blood sugar. However, the researchers note that they’re still unsure why isoprene levels rise when blood sugar drops, and there may still be other chemicals at play. Nevertheless, the study takes important first steps towards demystifying the work done by diabetes alert dogs, and could even help scientists develop new diabetes sensors.

“One of the things we’re hoping with this research is this might lead on to the development of some sort of sensing technology,” explains study co-author Mark Evans in the video below. “For example, we could even imagine something a bit like a breathalyzer that people with diabetes could use to detect hypoglycemia or even replace, at least in large part, the necessity to prick fingers to measure blood glucose.”

[h/t Gizmodo]