we release dopamine so we feel good about it. Between one and six per cent of people have a problem with sex behaviour and a problem with in terms of frequency or social consequences of the behaviour.

This may be so, but many still believe these so-called addicts should just exercise some good old-fashioned self-control.

It’s easy to look at a celebrity – like Duchovny, Douglas or Brand – and think that they have chosen to ‘out’ themselves as sex addicts rather than admit they’ve been caught cheating.

However Kelly disagrees – claiming there are three clear rules that define a sex addict as opposed to someone who’s just been caught with their pants down.

“The three core features of a sex addict are firstly, they have shown a loss of control, whether that’s using inappropriate partners or just showing compulsion to be involved with someone sexually.

“The second is the continuation of the behaviour despite adverse consequences. This relates to the level of risk-taking, for example dating when one’s away from home or continuing to engage in behaviours despite the extremely adverse consequences. Even if the person is afraid of being caught out, he or she continues.

“Finally, the third feature is they get withdrawal symptoms when they stop it. With sex addiction this tends to be feeling anxious or depressed – this is when it goes back to the biology of dopamine – where you only feel good when you’re engaging in this behaviour.”

“If you look at the internet, the most common search entry is sex and something like 40 per cent of men have looked at pornography in the last month, which is pretty staggering”

But is it just an addiction for celebrities? It’s rare that you’ll come across an ordinary member of the public who’ll admit they are a sex addict. Even Kelly agrees that one of the most notorious examples of a sex addict was the powerful leader Gengis Khan, who had hundreds of children.

While Kelly admits that celebrities have the added allure of fame and money – and therefore more access to sexual partners, he disagrees that the average person won’t become addicted.

In fact, the prevalence of sexual content available on the internet now means people don’t even need to be sexually active to become addicted.

“If you look at the internet, the most common search entry is sex and something like 40 per cent of men have looked at pornography in the last month, which is pretty staggering.

“What happens is they then get into a cycle where that behaviour is rewarding because of the dopamine. Viewing pornography then becomes habit-forming, a solitary behaviour which is associated with masturbating. They’re also getting visual material, so the internet is causing a lot of problems with sex addiction.”

While celebs are no more susceptible to sex addiction than the rest of us, men are more likely to become sex addicts than women, Kelly says.

As for poor Tea Leoni, should she stand by her man?

Kelly believes sex addicts can change and learn a new pattern of behaviour, but the risk of relapse is ever-present.