Dogs Can Smell Cancer, Low Blood Sugar, and PTSD Episodes Before Humans Even Know

The dog's nose has approximately 300 million olfactory receptors — roughly 50 times more than the 6 million in humans. The brain region devoted to analyzing smells is also 40 times larger, proportionally. As a result, dogs can detect chemical signals at concentrations as low as parts per trillion — equivalent to smelling a teaspoon of sugar dissolved in two Olympic-size swimming pools.

This sensitivity has remarkable medical applications.

What Dogs Can Detect

• Cancer: Trained dogs detect breast, lung, prostate, ovarian, and bladder cancer with up to 97% accuracy from breath, urine, or skin samples — often before traditional tests can find tumors
• Diabetic episodes: Diabetic alert dogs detect dangerously low blood sugar 15–30 minutes before patients feel symptoms
• Epilepsy: Some dogs alert their owners to oncoming seizures up to an hour in advance — possibly via subtle changes in body chemistry
• PTSD episodes: Service dogs trained for veterans can detect physical signs of an oncoming flashback, intervening with calming behavior
• COVID-19: During the pandemic, dogs were trained to detect COVID-positive sweat samples with up to 94% accuracy

Beyond Disease

Dogs are routinely trained to detect:

• Drugs and explosives
• Cell phones in prisons
• Bedbugs in hotels
• Endangered species' scat (for conservation tracking)
• Mold in buildings

Recent research suggests dogs can also detect emotions in human sweat. They appear to literally smell when their owner is afraid or stressed.