Sometimes you’ll see some body spray advertised as containing "pheromones" that can sexually excite the opposite sex. Scientists treat this idea slightly less respectfully than acupuncture (Scientific American):
But there is no evidence of a consistent and strong behavioral response to any human-produced chemical cue. “Maybe once upon a time we could react more viscerally,” says chemist George Preti of the Monell Chemical Senses Center. Today, however, our reactions seem to be much subtler—and harder to detect—than those of a silk moth. This subtlety has led researchers to propose another kind of chemical messenger, known as a “modulator” pheromone, that affects the mood or mental state of the recipient...
Yet to demonstrate definitively that pheromones are at work, researchers need to point to the molecules responsible, which they have not yet done. To date, scientists have collected evidence for possible pheromone effects but have not definitively identified a single human pheromone.
Meanwhile, while my wife and I are at work, our dachshund mix spends his day by dragging 3 or 4 our shoes up onto our bed.
Why does our dog surround himself with our shoes while we are away? Because our shoes smell like us. Is that all he smells?
It's only been very recently that scientists have realized that dogs and humans have spent the last 30,000 years evolving together. Under the previous theory, any scent signal used by humans for communication purposes would have to be sent by humans and received by humans. It's actually definitional:
What Are Pheromones?
Humans and other animals have an olfactory system designed to detect and discriminate between thousands of chemical compounds. For more than 50 years, scientists have been aware of the fact that certain insects and animals can release chemical compounds—often as oils or sweat—and that other creatures can detect and respond to these compounds, which allows for a form of silent, purely chemical communication.
Although the exact definition has been debated and redefined several times, pheromones are generally recognized as single or small sets of compounds that transmit signals between organisms of the same species. They are typically just one part of the larger potpourri of odorants emitted from an insect or animal, and some pheromones do not have a discernable scent.
This led to a clear scientific process: identify the smelly substances in our sweat and then see if other humans react to those smells. Long story short: humans can't smell very well and even at the unconscious level, we don't react to subtle smells.
Artificial selection vs. natural selection
Natural selection is amazingly creative because it literally tries everything and anything. No idea is too crazy to try. Endless random variations are trotted out, fail, are trotted out again in slightly different circumstances, fail, are trotted out again... Until some variation works just a little bit better than the previous way of doing it and gets reproduced down through the succeeding generations.
Artificial selection, the process by which humans domesticate animals and plants, is understood to be less creative. We can only encourage or discourage the traits we can see. Sheep had wool already, we just encouraged them to make more of it, with qualities that make it more pleasant when woven into clothes. (Artificial selection has, nonetheless, done some amazing things with maize, for example.)
Under the old theory of dog domestication, we selected wolves for their usefulness in our agricultural endeavors. The artificial selection which produced dogs was limited by the wolves we had to work with. We encouraged some wolf traits and discouraged others, but the creative power to generate new behaviors out of whole cloth is not available to mere mortals. Wolves would not have much use for making sense of human smells other than to avoid them. Presumably, we discouraged this trait by selecting and breeding wolf cubs that didn't mind our smell so much. At the very end of the day, we could hope they might even like they way we smell.
We don't research what we already know is impossible.
The scientific fact that humans cannot consciously smell human pheromones extinguishes completely the possibility that we could breed dogs that distinguish between human pheromones. I can train and breed dogs to identify a bomb with their senses because I can identify a bomb using my senses. I reward dogs that succeed at the task and then I breed them with other dogs who succeed at the task. This is useful because they use smell while I use sight. But I can't train or breed a dog to identify what I can't identify. How do I know which dog is good at it?
Dogs are the product of natural selection, and so are we!
But 30,000 years of co-evolution is a totally different ballgame. Natural selection can create traits out of whole cloth. Natural selection can breed dogs to distinguish smells that humans can't distinguish. And natural selection absolutely might not just cause dogs to distinguish between our different smells, natural selection might also cause us to produce smells that dogs can distinguish.