A dog’s sense of smell is its most developed sense. The ability varies between dog breeds based on the length of their nose. Dogs also devote more of their brain to processing smells.
For example – Kaelyn, a girl who suffers from mastocytosis, has a trained canine assistant dog named Jj. He has the ability to detect and alert someone before the start of a visible reaction to the girl’s illness.
Many service dogs have been trained and utilized to detect changes in a diabetic person’s blood sugar levels, ovarian, bladder and prostate cancer. There are also dogs that are being utilized to detect diverse things such as peanut detectors for those with peanut allergies.
A dog’s sense of smell is now being used to save human lives.
Source: Pet Tales: A dog’s nose knows