The Fascinating Ability to Detect Illness Through Scent

Your sense of smell is entirely natural. Each individual’s scent is a reflection of their biological composition, serving as a unique identifier and offering insights into their physical and mental state.

In the BrainStuff video above, Ben Bowlin explains how certain diseases alter body odor—diabetes, for instance, can make someone’s body smell like rotting apples, while typhoid fever emits the scent of fresh-baked bread. Yellow fever has a butcher shop-like smell, liver disease results in a fishy breath, and schizophrenia carries the scent of overripe fruit.

These distinct scents are linked to the way diseased cells metabolize. Diseased cells release different chemicals, known as volatile organic compounds (VOCs), than healthy cells. As these compounds change, so do the odors released from the body, particularly from sweat, blood, breath, and urine. A Swedish study recently revealed that the immune system's reaction to certain diseases can also generate unique scents.

The concept of detecting disease by smell is not new. It's believed that Hippocrates used scent to diagnose conditions by examining people's breath and urine. He was likely not the first, as the ability to detect odors has probably been an essential evolutionary skill, helping both our animal ancestors and modern humans avoid diseased companions.

The real breakthrough is that we are now uncovering just how powerful our sense of smell can be when it comes to identifying disease. For instance, a woman in Scotland noticed that her husband's body odor changed, becoming muskier as his Parkinson's disease advanced. Researchers at Edinburgh University challenged her to identify whether a group of test subjects had Parkinson's. She successfully identified 12 individuals — 11 already diagnosed and a twelfth who later developed Parkinson's eight months later, achieving a perfect success rate.

If some humans can detect disease by smell so accurately, imagine what dogs can do. A dog’s sense of smell is believed to be up to 100,000 times more sensitive than ours. They’ve been trained to sense blood sugar changes, the onset of seizures, and various medical conditions. They're also particularly skilled at detecting prostate cancer.

Several studies conducted by High Wycombe Hospital demonstrated that dogs were able to identify prostate cancer with 98 percent accuracy from 900 samples. The dogs could even distinguish between prostate cancer and other types of cancer. Furthermore, a recent *Scientific Reports* study showed that mice could detect Alzheimer’s disease through the scent of urine.

In the future, the natural instincts and training of both four-legged and six-legged scent detectors could be harnessed by a machine with extraordinary olfactory capabilities. A small, portable device called Cyranose (a clear reference to Edmond Rostand's play *Cyrano de Bergerac*) absorbs gases, analyzes them for specific VOCs, and diagnoses conditions like pneumonia or sinusitis.