Dogs are renowned for their sharp sense of smell. Dogs have about 220 million scent receptors than our 5 million, so they can smell things that seem baffling to us. They can identify some odors in parts per trillion, and they can sense countless subtleties in scents.

And yes, there are dogs who have sniffed out specific medical concerns that doctors weren’t even aware of. Dogs can pick up on tiny adjustments in the human body, from a small shift in hormones to the release of volatile organic compounds that cancer cells release. Researchers have only recently begun to understand how dogs are capable of this and how we might put them to work in being able to help us in health care.

Dogs are probably most famous for detecting cancer. Dogs have sniffed out various types, including skin cancer, breast cancer, and bladder cancer.

There are a fair few stories of a pet dog obsessing over their owner’s mole or a specific part of their body, only to later discover in a doctor’s appointment that the dog was sensing cancer.

Scientists have started seriously researching dogs’ sniffing abilities, especially when it comes to cancers.

For people who suffer migraines, having a warning before one comes on can mean managing the problem before hours or even days of terrible pain. Some dogs have a talent for sniffing out signs of an oncoming migraine.

Migraine sufferers with dogs have reported that they have noticed changes in their dogs’ behavior before or during a migraine. The results from different studies are fascinating, though it’s important to point out that many of these studies were conducted with self-reports rather than observation by researchers. Even so, the research shows evidence that many dogs seem to detect and point out a change in their human companion’s health.

One of the more controversial fields where dogs are used to alert to a medical condition is seizures. There is a growing body of evidence that dogs can detect the onset of an episode; however, the accuracy and, most importantly, our ability to train dogs to alert a handler to an oncoming seizure remains a bit dubious.

Dogs cannot be trained to predict seizures, but we can train dogs to respond to and assist a handler when an attack occurs. Some service dogs that are placed with seizure patients can develop the ability to detect when an episode is coming and alert if the handler pays close attention to the signals the dog offers.