Holding on to underwear for more than a year can lead to significant health risks, a new UK study has revealed.
Wearing old underwear allows bacteria such as E.coli to fester, which can lead to urinary tract and yeast infections, reports the Daily Mail.
According to The Good Housekeeping Institute, 83 per cent of clean underwear already contains roughly 10,000 living bacteria- a lot of becomes left in washing machines that rarely get their own clean.
A build-up of bacteria is another reason to sleep without underwear, the MailOnline reported last year. Failing to do so can even cause fertility problems.
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The study, first appearing in the Sun, explains that underwear should be binned every year in order to prevent bacteria accumulating.
It also explains how underwear should be changed daily.
One in four men wear underwear for two days before washing, the Sun reports, while women can wear the same pajamas for a fortnight.
An online survey conducted by Mulberry's Cleaners earlier this year revealed that 18 per cent of men and 10.5 per cent of women don't wash their underwear at all.
Changing pillows and bed linen every two years is equally necessary, as a mixture of dust mites and dead skin can increase the risk of allergies and asthma.