Hi Friends,

Just this morning, I was walking through my neighborhood when I watched three dogs meet.

Before any tail wagging or play began, one of the larger dogs immediately went in for a sniff — straight to the butt.

It made me smile… and then my doctor brain kicked in.

Why do dogs do this?

Dogs don’t rely on words or facial expressions the way humans do. They rely on scent — and scent is biology.

That quick sniff gives a dog an incredible amount of information. Chemical signals released from the anal glands and surrounding skin reflect hormones, metabolism, immune health, and the microbiome.

In just a few seconds, a dog can sense whether they’ve met before, whether the other dog is male or female, calm or stressed, and whether something feels off. This isn’t rude behavior in dog language. It’s social intelligence.

The microbiome plays a central role here. The bacteria living on and around the body metabolize secretions and create unique odor signatures. When the microbiome changes — because of diet, stress, antibiotics, inflammation, or illness — the scent changes too.

Humans send these signals too — we’re just far less aware of them.

In my practice, I often see patients whose primary complaint is a change in their breath. They’ll say, “I can’t explain it — something just feels off.” And more often than not, they’re right.

Changes in breath, body odor, or vaginal odor are frequently early signs of microbiome imbalance, sometimes long before testing shows any abnormalities. These are subtle biological signals the body sends early — signals we tend to mask rather than listen to.

Which brings us to something remarkable.

Dogs can smell disease in humans.

This isn’t folklore. Research has shown that trained dogs can detect certain cancers simply by smelling breath, urine, or skin. Dogs aren’t smelling “cancer” itself. They’re detecting changes in metabolic and microbial byproducts — volatile chemical signals released when cells behave differently under inflammation, immune dysfunction, or malignant transformation.

Even more fascinating, cancers themselves have microbiomes. Tumors are not sterile, and the bacteria living within them influence inflammation, immune signaling, and metabolism — all of which further alter the chemical signals released by the body.

Odor is one of the body’s most overlooked — yet powerful — indicators of health.

Dogs are remarkable animals, able to detect early shifts in microbial and metabolic signals through scent, made possible by a sense of smell up to 1,000 times more sensitive than ours.