Sex addiction was a term bandied around when it came to light that top-ranked golfer Tiger Woods had had a string of affairs behind his wife's back and was receiving therapy at a sex addiction centre.

But in an article last month on American news website The Daily Beast, psychiatrist T. Byram Karasu from the Albert Einstein College of Medicine/Montefiore Medical Centre in New York rejected the popular diagnosis.

He urged people to stop treating every human behaviour, including male libido, as an illness or a medical disorder.

"Sex addiction is simply a new name for the old evolutionary concept - the innate urge to impregnate as many females as possible. In this sense, every man is a sex addict, or was one at some point in his life," he wrote.

He also wrote that sex addiction, as it is commonly understood, is not like other addictions.

"Unlike addictions to alcohol, cocaine and cigarettes, in which the craving is induced by external elements, sexual craving, by its nature, is an innate and natural phenomenon," he said.

His position is in line with the American Psychiatric Association's Diagnostic and Statistical Manual (DSM) of Mental Disorders, which does not list sex addiction as an official diagnosis.

Psychiatrists in Singapore interviewed by The Straits Times similarly caution against using the term sex addiction too loosely.

But unlike Dr Karasu, they believe there is such a thing as sex addiction.

It involves a loss of self-control in which a person continues his behaviour despite adverse consequences, says Dr Thomas Lee, a consultant at the Institute of Mental Health's (IMH) National Addictions Management Service.

Marjorie Nixon, an American who was a therapist at the IMH between 2005 and 2007, has worked with such people for more than 20 years, both in Singapore and in the United States.

"It is one thing to masturbate occasionally and quite another to do it up to 20 or 30 times a day and in the process damage yourself physically," says Nixon, programme director of We Care Community Services, a voluntary welfare organisation that is an advocate for recovering addicts and their families.

Another comparison: A person may have multiple affairs and still be able to stop at will. But it is quite another story to wake up every morning already thinking of how to get sex and to seek out anonymous sex several times a day - and overlook the impact on one's health, marriage and job.

In replies to netizens' comments on his article, Dr Karasu clarified that it is a problem when an individual loses control over his sexual - or any other - behaviour.

But that is not sex addiction, he maintained. "Compulsive sexual behaviour is not sexuality; it is just another manifestation of severe obsessive-compulsive disorder."

In making his more fundamental argument that sexual craving is innate, his point of reference was evolutionary theory which posits that organisms with a larger sex drive will likely produce more offspring and may eventually dominate the population if sex drive is at least partially heritable.

Associate Professor Rudolf Meier, who heads the evolutionary biology laboratory at the National University of Singapore, says: "It's simple maths. If you have competition between organisms with a strong and a weak sex drive, the one with a strong sex drive will likely be over-represented in the next generation and this advantage will be transmitted to his offspring and so on."

Why the sex drive is greater among males than females and how it differs between animals and human beings requires more detailed explanation beyond the scope of this article.

Sex drive alone, however, does not account for errant sexual behaviour.

"Just because our genes may tempt us to seek out experiences that excite the pleasure centre in our mind doesn't mean that we have to follow these urges," notes Dr Meier.

"Being human means overcoming such biases and biological instincts."

Most researchers believe that sex addiction stems from psycho-emotional, not biological, factors, says psychologist Kit Ng, who has treated sex addicts in Singapore and in the United States for 15 years.

"You may have a very low sex drive and have sex addiction. It's what you do with sex and how you view sex," says Dr Ng, who runs a private practice in River Valley known as The Centre for Psychology.

A hint of the psychological issues is seen in the core beliefs of people with sex addiction, in a list drawn up by American psychologist Patrick Carnes, an expert on the problem.

For instance, they feel unworthy about themselves and think no one loves them as they are. They think their needs will not be met by others and that sex is their most important need.

IMH's Dr Lee also believes that people with sex addiction share similarities with people with drug and alcohol addiction.

They suffer physical withdrawal symptoms such as anxiety when they cannot get their fix.

They also build up tolerance to their 'drug'. One indicator is the file size of the pornographic videos downloaded from the Internet: It gets larger over time, notes Dr Lee.

Psychiatrists think it is a matter of time before more clinical research is done and sex addiction is recognised in the DSM, just as pathological gambling now is.

They believe that as more people recognise sex addiction for what it is, they will seek help.

"It allows people to rationalise in their own mind: 'This is why I am behaving this way and something can be done'," says Raffles Hospital psychiatry specialist Munidasa Winslow.

But the caveat remains that sex addiction should not be applied too loosely.

Dr Calvin Fones, a consultant psychiatrist at Gleneagles Medical Centre, notes: "A person with sex addiction will tell you they engage in it despite the fact that they don't particularly enjoy it all the time. Many feel depressed or shameful after engaging in it.

"It's different from someone who feels he needs to sow his wild oats."

He cautions: "Let's be careful not to label naughty boys as addicted. Society has this idea that once you are labelled, it reduces responsibility."