Pheromones are chemicals that send signals to other members of the same species. These signals could serve many purposes such as marking out territory (As dogs and cats do) or to mark a food trail (How ants all seem to converge on the same food source) or to send alarm signals warning other members of the species of impending danger.

However, the most widely known purpose and the one which has always attracted the most attention is the use of pheromones as a means of sexual attraction. Pheromones as a sexual attractant were identified as far back as 1956 when scientists extracted a compound from certain glands on the abdomen of the silkworm moth. This pheromone which they named bombykol was found to have an amazing effect on male silkworm moths. When exposed to it they immediately went into a frenzied "flutter dance".

But do pheromones work in the world of mammals as well? Studies done on hamsters and rats certainly seem to suggest they do. These studies also suggested that pheromones do not act directly on the normal olfactory senses. They do involve smells but they seem to act through a very specific channel.

Researchers believe that the vomeronasal organs are instrumental in picking up these specialized signals. The vomeronasal organs or VNO's are tiny cigar-shaped organs found in the nostrils which appear to communicate directly with the parts of the brain that control reproduction and parenting behavior.

That's all very well but do these same mechanisms of attraction and behavior modification apply to the most complex of mammals - man himself? This has long been debated. Sense of smell is perhaps one of human beings least used senses and given the world we live in we perhaps need to rely on it less for survival than other primitive mammals.

On the other hand a multi-billion dollar worldwide perfume industry is ample proof of the importance that most of us place on odors and perhaps the lengths to which we go to mask what we consider to be undesirable smells. But do humans have naturally occurring pheromones which impact on the lives of others in the species?

Several studies have shown promising results. Dr. Winifred Cutler, a biologist and behavioral endocrinologist, found pheromones present in underarm secretions. She also found that women who had regular sex with men had more regular menstrual cycles. Pheromones which had been identified in the under arms of men contributed significantly to this outcome.

Another notable study was conducted by Martha Mclintock in the 1970's when she observed that the menstrual cycles of groups of women who lived together tended to become synchronized. Further study revealed the startling fact that it was exposure to pheromones from other women which caused the changes in cycle.

Test subjects were exposed to sweat samples collected from other women. Their menstrual cycles slowed down or sped up depending on the time of month when the samples had been collected. The implications of this discovery for treatment of infertility or even contraception are obviously extremely exciting and it has been suggested that pheromones could also be used to alter mood and alleviate depression and stress.

Pheromones are also likely to be the scientific basis of the romantic concept of "chemistry" between individuals - that feeling of an instant attraction and connection with certain people. There is also evidence that we seek out mates whose immune systems complement ours. In other words we are instinctively attracted to people whose immune systems are most different from our own. This ensures the production of the strongest and healthiest offspring. Our instinctive actions are based on the pheromonal signals we pick up.