That’s what our friend, germ specialist Dr. Philip Tierno wanted to know! He recently surveyed the hygiene habits of more than 20,000 people across North America. Here’s what he learned:

• Let’s start with: Your bed. Dr. Tierno recommends changing your pillowcases and sheets every week, to guard against the build up of dust mites, and lower your risk for bed bugs.

But this survey found that at least one-in-four people wait a month or more to change their bedding.

• Next: Your shower. Dr. Tierno says bathtubs and shower stalls need to be scrubbed and disinfected weekly, to remove the build-up of “biofilm.” That’s the thin layer of dirt, sweat and grime that you leave behind every time you step out of the shower. But this survey shows that about half of all people wait anywhere from a month to six months to scrub the tub.
• Finally, how hygienic is your fridge? Dr. Tierno says refrigerators should be cleaned at least once per month to limit your exposure to sickness causing E-coli and salmonella. But a whopping 40% of people surveyed say they wait anywhere from three months to a year before cleaning their fridge.