While scientists agree on which part of the brain is associated with love, pinning down the patterns of attraction which induce these hormonal reactions is harder.

Clinical psychologist Yam Keng Mun, executive director of the Centre For Effective Living, said people tend to fall in love with someone of the same general level of intelligence, looks and religion.

He said that latest research shows that people tend to be more attracted to people who look like their parents.

'People are more likely to be more attracted to those who have facial features they can associate with. This triggers off the same chemistry of love they have with their parents,' Mr Yam added.

As a result, we are imprinted with sexual impressions from frequent exposure to our parents since childhood, which leads to certain preferences in our partners with characteristics similar to our parents.

Other psychologists like Professor Robert Kurzban, from the University of Pennsylvania, said that for men, it is the woman's body mass index (BMI) and facial symmetry that determines attraction.

For women, attraction is based on BMI as well as cues about health and social status like income and education, msnbc.com reported.

Evolutionary psychologist Devendra Singh, from the University of Texas, said - desirability-wise - the woman's waist-to-hip ratio plays a role too because it transmits signals about her health and fertility.

Research also shows that women, particularly around ovulation time, are highly sensitive to male pheromones, which is the body odour that induces sexual arousal.

In fact, scientists at the Helen Wills Neuroscience Institute, University of California at Berkeley, found that a chemical component of male sweat triggers higher levels of cortisol, the stress hormone, in females.

However, the Social Issues Research Centre in Britain argues that not all male pheromones are equally attractive.

The male pheromone androstenol, produced by fresh male sweat, is attractive to females, but it disappears very quickly. Androstenone, which is produced after sweat is exposed to oxygen, becomes more prominent and actually repels the female senses.

Meanwhile, with more people meeting online and finding their partners in virtual space, researchers are looking into how attraction is established without visual and physical contact.

Dr Brian Yeo, consultant psychiatrist at the Mount Elizabeth Medical Centre, argued that it may be easier to find attraction online since people with common interests naturally join the same groups and chat rooms on the Internet.

The anonymity of the Internet also gives people a sense of security in disclosing more about themselves to the other person. This allows them to establish rapport more easily.

'The connection with people online develops much faster because people can create an ideal persona that may not be true in reality and no one will know,' he said.

People are also mentally prepared to be stimulated when meeting a potential mate online.

'Their hormones are already charged up when going online and they kick in very fast,' Dr Yeo said, adding that meeting offline results in slower hormonal reactions but have more sustained effects.

In fact, if the right buttons are pushed, the body experiences an adrenaline rush, triggering the release of dopamine, which induces oxytocin in the brain. The result: the same physical sensations of love and reinforced sexual activity, he said.

However, to make an online relationship last offline as well, psychologist Tsai Fen-Fang from the National University of Singapore said couples have to start on a relatively honest level online in order to avoid eventually disappointing the other person and vice versa.

This article was first published in Mind Your Body, The Straits Times.