Hardly anyone would dream of wearing a set of work clothes for three days in a row, but, as it turns out, most of us wouldn’t bat an eye at the thought of wearing the same pair of pajamas for weeks at a time. And it’s a habit that could affect our health.

According to a new poll conducted by Ergoflex, a mattress company, the average man changes his pajamas every 13 days. The average woman waits a whopping 17 days before she pulls out a new pair and throws the old ones in the laundry.

When asked about the issue, professor Sally Bloomfield of the London School of Hygiene & Tropical Medicine, told MailOnline, “Pyjamas [that's British for PJs] are against your skin. You shed skin cells at a vast rate all the time. They are full of microorganisms. We all have skin and gut organisms that are usually not harmful on our skin and in our gut. But if they get into the wrong place, they can cause problems.”

What kinds of problems? Bloomfield explains: “Quite a lot of us carry staphylococcus bacteria, which can cause infections if they get into cuts and bruises. We all carry E. coli bacteria in our bowel. Again, most strains are not harmful. But if they get into the urinary tract, they can cause infection. That would cause cystitis (a urinary tract infection). Some people carry MRSA (Methicillin-resistant Staphylococcus aureus), which obviously gets very hard to treat, especially with antibiotic resistance.”

Men vs. women

Ergoflex polled 2,410 British couples between the ages of 18 and 30 years old, asking them what kinds of PJs they wear and how often those sets get tossed in the hamper. Just about half (51 percent) of the women noted that because the clothing was only worn for a few hours a night, they didn’t believe it needed to be washed as frequently.

The men sang a different tune, with 73 percent explaining that because their partners did the laundry, they had less control over how often the clothes were cleaned.

Both men (50 percent) and women (41 percent) relied on their sense of smell to determine when their pajamas were dirty. And both noted that, because they only owned a few sets of pajamas, clothing wasn’t swapped out as often as it should be.

How often should you wash?

Bloomfield recommended that people should change their nightwear at least once a week to prevent the buildup of dangerous microbes. She said, “Washing should get rid of most microbes, but not all if you have worn them for two weeks. The clothes won’t be hygienically cleaned because the microbes will have built up. So they will be transferred to underwear and other clothing that comes into contact with the skin.”

While this isn't particularly off-putting if you live alone, Bloomfield notes that it becomes a bigger issue if you share your home with others, such as multiple roommates or family. The harmful microbes could spread to other people in the household. And in that case, sharing is definitely not caring.

Happily, this is a problem with a simple solution. By putting the smell test to rest, buying a few more sets of pajamas, and making sure to wash our night clothes more frequently, we can reduce our exposure to E. coli and MRSA and keep ourselves and our loved ones healthier and happier.

So, how often do you change/wash your PJs?