Michael Douglas says cunnilingus gives you cancer – but is he right?

Actors are often accused of being irritatingly reticent about their private lives – unwilling to satisfy fans' and journalists' curiosity about aspects of their life off the film sets.

But that's not something that can be said of Michael Douglas' latest interview, with Xan Brooks, for the Guardian. Asked whether he ascribed his 2010 throat cancer diagnosis to a lifetime of drinking and smoking, he replied particularly frankly:

"No. Because without wanting to get too specific, this particular cancer is caused by HPV [human papillomavirus], which actually comes about from cunnilingus."

"I did worry if the stress caused by my son's incarceration didn't help trigger it. But yeah, it's a sexually transmitted disease that causes cancer. And if you have it, cunnilingus is also the best cure for it."

So, now that's out there, how much of it is true? Is oral sex linked to mouth and throat cancers? Is there a difference between the genders? And what can be done? We've dug into the stats – especially this NHS guide – to dig out a few answers.

HPV and you

There are more than 100 variants of HPV, otherwise known as the human papilloma virus, and they appear in different parts of the body and manifest in different ways – some, for example, can cause warts (including genital warts), while in most cases most appear symptomless.

Some are spread simply by skin-to-skin contact, while others are typically spread during sex. It's these latter types that are typically found in the mouth, suggesting that when HPV is found in the mouth, it's probably got there as a result of oral sex. HPV can also be spread to the relevant areas through vaginal and anal sex.

HPV is really, really common – to the point that if you're a sexually active adult, you've probably had it. By the age of 25, 90% of sexually active people will have been exposed to some form of genital HPV (whether high or low risk), almost none of whom will ever have had any visible warts or other symptoms.

HPV and cancer

Around 15 types of HPV are linked to increased cancer risk, and it's been associated with oral cancers, cervical and vaginal cancers, as well as anal and penile cancers.

HPV increases cancer risk, but can't be explictly said to have caused any particular cancers (though some variants are HPV-related and others not): just because someone with cancer also has HPV doesn't necessarily mean they wouldn't have got it anyway.

It's also a long-term risk factor: over years and decades the risk is increased, rather than overnight.

When it comes to oral cancers, here's a rough guide to the statistics. In 2010, around 6,000 people were diagnosed. For comparison, in 2010 there were also 2,850 diagnoses of cervical cancer and 49,900 diagnoses of breast cancer.

Noting the above caveats, it's calculated that between 25% and 35% of oral cancers are HPV-related – meaning it seems to be involved in somewhere between 1,500 to 2,000 diagnoses a year.

Men vs women

So – is cunnilingus inherently riskier than fellatio? While studies on sex differences aren't entirely clear, a US study found the prevalence of HPV in the mouths of men was 10%, versus 3.6% for women. Overall, HPV-related oral cancers are most common in heterosexual men in their 40s and 50s, leading the NHS guide to conclude that:

This indicates that performing cunnilingus (oral sex on a woman) is more risky that performing fellatio (oral sex on a man). This seems counterintuitive, but the concentration of HPV in the thinner moist skin of the vulva is mugh higher than the amounts of virus shed from the thicker dry skin of the penis, and this affects how easy it is to pass the virus on.

The HPV vaccine

Teenage girls in the UK and elsewhere are now vaccinated against HPV, which should in time both protect themselves from cervical cancers and – it's believed but not yet been demonstrated – future partners from HPV-related oral cancers.

Evidence from Australia suggests things are working, with genital warts (a good short-term proxy) falling markedly in women and heterosexual men in the years after the introduction of a vaccine.

The one group the current vaccination programme does nothing to protect, of course, is men who have sex with men – who are at increased risk of several cancers due to HPV.

So ... smoking's exonerated?

Douglas used HPV to exonerate smoking for his particular cancer. Unfortunately, the evidence suggests he wasn't quite right to do so. Most people rid themselves of HPV within a few years of catching it – but smoking disrupts this process, meaning the virus remains for far longer in smokers than non-smokers, increasing their risk of HPV-related cancers of all varieties.

Smoking is also, of course, a substantial risk factor for non HPV-related oral cancers, as well as lung cancer.

Staying safe

Unfortunately, there doesn't seem to be much research evidence to back up Douglas' claim that the cure for throat cancer is still more cunnilingus.

One thing that can help, though, is using a condom or a dam during oral sex, the NHS says. It also helps protect against other orally-transmitted STDs too, such as chlamydia and gonorrhoea.

Any other studies or evidence we should've looked at? Anyone got some other good stats on the topic? Let us know below...