One study tested smartphones belonging to secondary school students. Not only were the phones loaded with potentially harmful bacteria, but researchers hypothesized that they also contributed to the spread of illnesses throughout the community. OK, so you probably suspected teenagers were doing that anyway, but what about doctors and nurses? Surely, they of all people understand the importance of keeping things clean? That's ... not what the evidence says.

Studies carried out everywhere from the U.S. to Egypt to Australia tested phones belonging to hospital workers and found that a clear majority (75 to 100 percent) carried bacteria. In France, 42 out of 109 hospital workers' smartphones carried viruses, while in Turkey, 25 out of 200 tested positive for MRSA -- you know, that superbug that fills your body with pus-oozing boils. So if you've got a hospital stay coming up, here's hoping your phone-addicted doctor doesn't have another patient with flesh-eating bacteria.

To top it all off, you're probably making the problem even worse by storing the bags in the trunk of your car. While that might seem like the most convenient place to keep them, bacteria love the warm, dark environment, and will seize the opportunity to reproduce. Rapidly. That's right, if the junk in your trunk includes your shopping bags, you're probably the proud owner of a s**t bacteria ranch you never knew about.

The solution? There are lots of tips to prevent bacteria from getting out of hand, but the most important is to wash those freaking things. That, or learn to juggle a large number of items and do away with bags altogether.

Researchers at the University of Colorado Boulder found that shower heads have a way of concentrating nasty bacteria. Specifically, 15 out of the 50 shower heads they analyzed contained Mycobacterium avium, which is linked to pulmonary disease. That stuff was always in the water; the issue is that shower heads are remarkably good at accumulating it and then blasting it right at your face while you think you're cleaning yourself.

University of Colorado Boulder

University of Colorado BoulderHmm, maybe cats have the right idea ...

Oh, and you know that soapy crud that builds up on your shower curtain? That's a biofilm containing more than a billion bacteria per cubic inch. Between the shower head and the curtain, you're basically surrounding yourself with bacteria, and when you add splattering water and steam to the mix, you're effectively "enmeshed in a bio-aerosol" of germs. Which is as healthy as it sounds.

In fact, according to the National Jewish Hospital (but this applies to all religions that believe in bathing), dirty shower heads are largely to blame for the increase in respiratory infections caused by "non-tuberculosis mycobacteria" (NTM). One study worked backwards, testing the shower heads in the homes of 20 patients with NTM infections. Mycobacteria was present in all but one home. And it gets even worse. One shower head that researchers found loaded with mycobacteria was treated with a bleach solution to get rid of the nasties ... which resulted in a threefold increase. This means the species of bacteria is, or is becoming, resistant to chlorine. Quick, go take a nice hot bath before we find out that's somehow killing you too.

Multiple studies have shown that kitchen sponges are absolute breeding grounds for bacteria, and while you might not be surprised to hear that they're dirty, you should be shocked at exactly how much and what kind of bacteria are lurking in that thing you rub all over your eating utensils. A British study estimates that the average sponge harbors a whopping 19.6 billion bacteria. What kind? Another study, this one from Germany, found that most kitchen sponges contain E. coli and salmonella, and are the "biggest reservoirs of active bacteria in the whole house." Yes, bigger than the place where you drop your poop.

Kameleon007/iStockWho lives in a pineapple under the sea? SAL-MO-NEL-LA!

Before you pat yourself on the back for regularly cleaning your sponge, we have more bad news for you. One study found significantly more bacteria in sponges that were regularly sanitized, which means there's little hope for getting a sponge truly clean once it's seen use. Researchers recommend replacing your sponge about once every week, and not "whenever it starts falling apart," as we've been doing until now.

See, regular washing doesn't kill germs in laundry, so your machine collects bacteria from all the clothing and linens from all the people and pets in your household. The accumulated germs sit there and chill until they have the chance to party on your clothes or your hands when you touch wet laundry. Now, if you have your own washing machine and live alone, you're pretty much just recycling your own germs. But if you share a machine with other people? Then you're wearing their funk on your body every time you put on your clothes. That weird guy from the laundromat might as well have rubbed his sweaty butt all over you.

spyderskidoo/iStock"OK ... 'Reg Load,' 'Perm Press,' 'Ass.' Perfect."

One study from the University of Arizona (which has a whole building devoted to filth-related research, it seems) found that a single germ-laden article of clothing "infected" 90 percent of the load it was washed with. This becomes a huge problem when someone sharing your washer is sick, since most "organisms that cause colds, flu and stomach flu ... will survive the wash cycle." How can you get rid of the Petri dish inside your washer? Experts recommend periodically letting it go through a wash cycle with no clothes, just bleach and water. You can also hang your clothing to dry in the sun, as UV radiation kills even the most stubborn poop and flu bacteria. Alternatively, wait for the sun to expand and cleanse the entire world with its beautiful, purifying fire.

Getting a new shower head might be a good idea -- check out this one that changes colors!

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For more, check out 6 Items You Touch Every Day That Are Filthier Than A Toilet and 6 Everyday Things You Had No Clue Were Made Of Dead Animals.

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