Do humans secrete chemicals that attract the opposite sex? Some cheesy advertisements in magazines would make one believe pheromones exist. When's the last time you said "that girl/guy is butt ugly", then walked closer to smell her/him and said "damn girl/boy, you fine!"?
There are many perfume companies offering products that claim to contain human pheromones, and this one has an interesting claim on its home page that attempts to convince potential customers:
Unfortunately, there don't seem to be any references to studies on that web site regarding any types of Pheromones -- I would like to see even one study they're relying on to back up their claim that "Animal Sex Pheromones are well documented in the animal kingdom as the force that controls all social behaviour, including mating," which is a good reason for you to be skeptical.
People do have olfactory systems that help to discern smells though, and since people do exhibit a variety of natural odours (possibly influenced by a combination of genetics, state of health, diet, exercise habits, etc.), I would expect the effects to be at least somewhat selective since what is perceived as a bad smell by one person may be a good smell to another. There is an interesting paper on this that references a long list of studies, including some studies performed on rats (in particular, see the sections entitled "Human Pheromones" and "Is a Mammalian Model Applicable to Human Behavior?"):
Human Pheromones: Mammalian Olfactory, Genetic, Neuronal, Hormonal,
The first paragraph in the "Introduction" section (paragraph 3) reads:
The first paragraph in the "Human Pheromones" section (paragraph 9) reads:
The fifth paragraph in the "Is a Mammalian Model Applicable to Human Behavior?" section (paragraph 53) reads:
Hypothetically, if these pheromones were powerful enough to have an immediate effect on a person so as to completely change their perception of how attractive another person is, then I strongly suspect that these products would likely be classified as dangerous (since they could be used to commit crimes of a sexual nature, etc.) by local government regulators (just like many pharmaceuticals are) with their distribution prohibited (which would consequently make it illegal to sell).
So, in an attempt to answer your questions: It seems that Humans do secrete these chemicals, but I would classify the rest of the exaggerations and claims by the marketers as something along the lines of mythical.
To answer your question "Do human pheromones exist" the answer is most certainly "yes". That's what body odour is.
Your question should be "Do human pheromones work the way the scam artists say they do". The answer is almost categorically "no". It's already pretty apparent that your natural pheromones aren't attracting the opposite sex like sharks to blood. More than likely the reason for this is because human beings just don't operate (or mate) like dogs or moths. We all meet and mate through social mechanisms instead. I suspect that the effectiveness of your pheromones on other people is a highly subjective and individual thing and just as importantly, only part of the equation.