When did you last wash your pyjamas? A mob of Mumsnetters has worked itself into a lather about whether one’s PJs should be washed after every wear. “Oooh, a laundry thread,” as one forum user succinctly put it: “Get ready for neurotics versus mingers …”

It turns out, there really are people who wash their nightwear every day. “People sweat in bed, and many will go to bed without washing, as they shower in the mornings, so that is enough reason for me to wash PJs after one night,” wrote one member of the cleanliness camp. But there are clearly plenty of “mingers” content to wait days or even weeks between washes. A 2015 survey, by the mattress company Ergoflex, of nearly 2,500 people aged between 18 and 30 revealed that men wait 13 nights on average between washes, while women go 17 nights.

A key determinant of how long people will put off purging their PJs appears to be the pong factor: 41% of women and 50% of men said that if their nightwear didn’t smell, they didn’t see why it needed washing.

So, which side is right? Over to Prof Sally Bloomfield, chair of the International Scientific Forum on Home Hygiene. “We all carry certain organisms that are potentially harmful to us if we get them in the wrong place and are potentially harmful to other people if they get transferred to them,” she says. “Why do we launder in the first place? Because we don’t want other people to get those organisms.”

Such bugs include skin bacteria, one of which is Staphylococcus aureus, a common cause of skin infections; fungal organisms such as the one responsible for athlete’s foot; faecal bacteria, such as E coli, which occasionally cause stomach upsets; and yeast, which can trigger thrush.

Bloomfield, who, for the record, says she wears nothing in bed, washes her sheets approximately once a week – although she shares a house with only one other person, her husband, which is a crucial determining factor. Some people are more vulnerable to infections, while others are a more potent source of dangerous bugs. If you live with young children, or someone in your family is obviously ill, the need for regular laundering of bedclothes is more pressing, she says.

Garments should be washed at 60C or at 40C with a product containing active oxygen bleach, in order to remove and destroy bacteria. Overloading your washing machine – as you might if you were trying to wash a family of five’s pyjamas, plus everything else each morning – will not do the job and may simply spread the bugs further afield. Plus, some nasties – including the bug responsible for norovirus – can survive on dry fabrics for weeks.

So, what of the stereotypical bachelor, happily stewing for weeks in a single pair of underpants? Here, the risk is lower, says Bloomfield, because our own organisms usually start to threaten our health only if they get into the wrong places. “The dirtier your pyjamas get, the more likely it is that things will be transferred from your bowel to your urinary tract, for example. You can’t say there’s no risk, but the risk is relatively low.” There is, however, the issue of personal hygiene to consider. “Your underwear or pyjamas will start to become nasty smelling, and nasty feeling if you don’t wash them regularly.”

As for what constitutes regularity, Bloomfield suggests once a week is adequate, unless your pyjamas - or whatever else your body comes into contact with - is visibly soiled. You can, of course, wash them more often, but there is the environment to consider: washing and drying a load every two days generates around 440kg of CO2e each year – equivalent to flying from London to Glasgow and back. And, if you dry your clothes by sticking them on the radiators or indoor drying racks, you risk creating the moist conditions in which mould thrives – another health risk. In other words: at ease, mingers.