Nearly 40 per cent of British adults sleep in pyjamas, a little more than 20 per cent in their underwear and just under a third wear nothing in bed, according to a survey of 1,200 adults.

Since the average length of time between pyjama washes is two weeks (the most common excuse people gave was that their nightwear didn't smell), you might think being naked is healthier. After all, your skin needs to breathe, doesn't it?

There is not a lot of research on the topic. But first off, skin does not breathe.

The idea that air will waft over our naked bodies and we will somehow soak it up just isn't true.

However, sleeping naked does keep you cooler - the optimal temperature for sleeping is around 20 deg C.

Lack of sleep is linked to a multitude of conditions such as diabetes, obesity, stroke and depression. It is also corrosive to relationships.

If you are too hot in bed, then your core temperature will struggle to fall which, according to the United Kingdom-based The Sleep Council, means you won't trigger your "sleep mechanism".

During sleep, your body's temperature falls naturally after three or four hours - and wearing fluffy pyjamas under a heavy duvet will disrupt that.

However, your feet mustn't get too cold, as that also disturbs sleep. Rather than wearing bed socks, which get hotter by the hour, you should use a hot water bottle.

Then, there is the sex and reproductive health angle. Wearing underwear at bedtime increases the likelihood of your genital region getting sweaty, especially in summer.

For women with conditions such as vulvitis, an inflammation of the outer genitalia in which the skin folds are red and swollen with tiny cracks, wearing underwear in a warm bed can encourage opportunistic infections such as yeast that thrive in dark, sweaty crevices.

According to a study in Andrology, men who don't wear pants at night may improve the quality of their sperm.

Data from about 500 men in the United States shows that those who wore boxers during the day and nothing at night had a 25 per cent lower risk of DNA fragmentation in their sperm than those who wore tight pants night and day.

However, the study didn't show that their partners were more likely to get pregnant or to do so more quickly.

Research in the Journal of Urology found no significant difference between underwear types and semen quality. "It is highly unlikely that underwear has a significant effect on male fertility," concluded the authors.

In the absence of any evidence, except that most pyjamas are dirty and you shouldn't overheat, the choice of whether or not to use nightwear is not a health issue.

But in the case of those people in surveys who said they wore tracksuits - they really are not for sleeping in.

THE GUARDIAN