Fido Authority

Dogs have wet noses because it helps to absorb scent chemicals. Dogs can be trained to detect cancer and other diseases in humans. Cancerous cells release different metabolic waste products than healthy cells in the human body. Dogs may even be able to sniff out cancer cells simply through smelling a someone's breath. . 

Unlike humans who have sweat glands over most of their bodies, The ajority of a  dog's sweat glands are located in their paws. A dog who is overheating may leave behind a trail of wet paw prints on the floor or pavement; this is a signal that it’s time to help your pal cool down.

In fact, your dog's sense of smell is approximately 100,000 times better than yours. So it shouldn't be shocking that they can in fact, smell things such as fear. When a human is fearful, they perspire, and a dog is easily able to pick up on this change.