Condoms should be changed during long sessions in the sack to lower the risk of unplanned pregnancies and sexuality transmitted infections, say experts.

A recent study, where 500 couples from a number of countries timed how long sex lasted using a stopwatch, found on average intercourse lasts around 5.4 minutes.

However times from 0.55 seconds to 44.1 minutes were recorded.

And more prolonged friction from sex can have a detrimental impact on the ultra-thin latex condoms are made from, if they're being used. 

For this reason, top sexual health experts advise switching your 'rubber' after 30 minutes of activity, and possibly more often if intercourse is particularly vigorous.  

Research shows that condoms are up to 98 per cent effective at preventing pregnancy used correctly.

If not used correctly they become less effective and it is estimated that around one  in five women who use condoms for a year will get pregnant.

Studies have also found condoms are 95 per cent effective at stopping HIV and other sexually transmitted infections, again with correct use.  

Incorrect use includes putting a condom 'too late', after intercourse has started and a condom coming off or breaking during sex.

In an article on the LloydsPharmacy website, GP Dr Neel Patel states: 'It probably comes under the bracket of a good problem to have, but if you've been going for half an hour and aren't ready to stop, change the condom.

'Friction weakens the condom, increasing the chances of a break. Under 30 minutes and you’re fine. Over 30 minutes and it’s best to play safe.'

He adds: 'Obviously the amount of friction depends on how vigorous your intercourse is.'

Dr Patel also advises against 'double bagging': the practice of wearing two condoms at once for extra protection, which he says is a myth.

'Wearing two condoms is actually riskier than just wearing one as they will rub against each other, creating potentially condom-breaking friction.'

Apparently the same caution should be applied to using a male condom in tandem with a 'femidom', or female condom.

The NHS advises, before putting on a condom, to make sure the penis is fully erect first.

The packet should be opened carefully to avoid damaging the condom. Do not use your teeth as this could rip the condom.

Hold the tip of the condom to squeeze out any air. Roll the condom all the way down to the base of the penis. 

It adds that, if the condom does not roll down, it may be on inside out. If this occurs, the condom should be thrown away and a new one used. 

Dr Patel says care should be taken if lubricants are used. 

'Certain lubricants do not agree with latex,' he advises. 'Water-based lube is fine. Oil-based or petroleum-based lube should never be used.'

Body lotions, moisturiser and massage or body oil are also not substitutes. 

'These can weaken the latex, causing the condom to break,' he explains. 

Condoms should be kept on until sex is over. When you've finished, grip the base of the condom as you pull out to stop it coming off the penis.

Always put used condoms in the bin, not in the toilet.