Phermones as defined in Wikipedia - a chemical that triggers a natural behavioral response in another member of the same species. There are alarm pheromones, food trail pheromones, sex pheromones, and many others that affect behavior or physiology. Their use among insects has been particularly well documented, although many vertebrates and plants also communicate using pheromones."
In laymans terms, phermones are a naturally occurring chemical produced by insects, animals and people. Just like how sweat glands are produced with certain activities. When these chemicals are secreted, they influence sexual behavior and attract the opposite sex.
Phermones are odorless. They are an integral part in sexual communication. Mostly they come along with perspiration but they can also come in the saliva and tears. What they do, is give signals to the opposite sex's subconscious awareness regarding the sexual status of the person giving them out - the mood, health, virility, etc. For males, a dominant, aggressive, and testosterone filled person will excrete phermones in larger amounts thus will be chosen over more times than a male who is submissive. For females, the more feminine behavior will attract males.
There has been studies too that suggest that phermones can travel great distances. For example, in the animal kingdom, they use phermones to mark their territory. With female animals, when they are in heat, the resulting phermones produced, attract males of the same species even from great distances. I had a dog once who had frequent visitors waiting in front of the house every time she was in heat.
Although there has been a lot of skepticism regarding the existence of human phermones, there have been multiple studies done by scientists, universities, media, and even everyday people to see the effect of phermones. Thru this research, the human phermone - Androstenone - was discovered. This is a male phermone to attract women.
It was discovered that this male phermone comes along with perspiration. It is ironic that something which attracts, comes with something that is unattractive. With a lot of our modern commercialized cleaning and bathing, males have cleaned themselves out of our naturally occurring attractor. It is still unclear on why evolution has chosen to put sweat and phermones together.
So what can a guy do from here? Not exercise proper grooming and hygiene?
This is where the advent of commercialized phermone colognes and perfumes came about. These manufacturers claimed to have isolated the naturally occurring phermones of both males and females and mixed it with pleasantly smelling concoctions.