LONDON — You probably would not wear the same unwashed pair of underwear for two straight days, but when it comes to pajamas, well, that appears to be a different story.

A poll conducted by a British mattress company found men, on average, go 13 days in between pajama washings. It’s even longer for women who go, on average, 17 days without washing their PJs.

Of the reasons behind why nightwear is washed so infrequently, the top result for women (54 percent) was that by alternating between multiple pairs it’s easy to forget how long they’ve been out for, while men mainly claimed that they didn’t do the washing so just wore what was to hand (73 percent). When it came to particular hygiene considerations, 41 percent of women and 50 percent of men claimed that since their nightwear didn’t smell (to them at least), they didn’t see why wearing them for such long periods was a problem.

“Pajamas are against your skin,” London School of Hygiene and Tropical Medicine Sally Bloomfield told MailOnline. “You shed skin cells at a vast rate all the time.”

She said while most of those cells are harmless, “if they get into the wrong place they can cause problems.”

Bloomfield recommended washing pajamas at LEAST once a week.

“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,” she said. “So they will be transferred to underwear and other clothing that comes into contact with the skin.”