One of the first things we learn as kids is that it’s important to wash our hands. Handwashing helps prevent disease spread. It can keep an office running instead of shutting it down due to a viral illness. It’s especially important to wash your hands if you are interacting with newborn children or potentially vulnerable elderly adults.

But we don’t always appreciate the reason why handwashing is so important: we touch a shocking number of filthy surfaces every single day. Here are some of the most surprisingly dirty things we come into contact with on a regular basis.

It turns out that the thing you use to wash your dishes is teeming with bacteria. In fact, many microbiologists identify it as the dirtiest single item in your household (far, far dirtier than your toilet seat).

Sponges, which are often warm, wet, and have traces of food on them, are ideal breeding grounds for bacteria. One NSF (formerly, the National Sanitation Foundation) study found that more than 75% of sponges were contaminated with coliform bacteria, which indicates faecal contamination and from the same family as Salmonella and E. coli. Campylobacter, the biggest cause of foodborne illness in the US, is also commonly found on sponges.

Tierno recommends using bleach to clean your sponge.

Knowing that your sponge is dirty, you might be inclined to wash your hands after doing the dishes. That's wise!

But unfortunately, reaching to grab the dish towel that you keep by the sink might undo some of the good you did by washing your hands in the first place. Dish towels frequently have the same issues as sponges, since they're also damp, warm, and come into contact with food particles. One study found E coli. on more than 25% of dish towels, putting them firmly into competition with sponges. Wash them after two days of use.

The fact that your kitchen and phone are so dirty might make you want to bury your face into your bedsheets. But when did you wash them last?

Beds share many of the same characteristics that bacteria love. Humans sweat a lot, so they're wet and warm -- ideal for bacteria and for fungal growth. And our skin particles rub off onto our sheets along with everything we've come into contact with during the day. The result is enough to make a germaphobe wince. Wash your sheets once a week or so, say experts.

Your grocery cart is perfect for holding your produce, children, and E. coli. It turns out that when people walk around the grocery store -- with potentially unwashed hands -- grabbing food, including wrapped up raw meat and whatever else catches their eyes, they can transfer some unsavoury bacteria from their hands to the cart and vice-versa.

One small survey found bacteria like E. coli on more than half of carts, which the authors say could be responsible for outbreaks of food poisoning among children who ride in carts.

Hopefully a theme is becoming clear. Things that you and many other people touch frequently with their hands quickly become hotbeds of bacteria, especially if they're not wiped down regularly.

Doorknobs are no exception. Some research has found tons of potential pathogens on doorknobs, other research much less, but either way, it doesn't take a lot to get sick. One microbiologist found that after placing a virus on an office door push panel, it took only four hours for more than half of people in that office to pick it up -- and that virus made its way to over half of commonly touched office surfaces in same span of time.

Your toothbrush goes in your mouth and then back into some sort of holder on the sick. At the same time, that bathroom air is full of whatever your toilet kicks up with a flush. That little toothbrush holder, it turns out, is perfect at picking up whatever bacteria is around.

One survey found staph bacteria on 14% of toothbrush holders and yeast or mould on 64%. Clean those containers.

Potentially pathogenic bacteria are clearly everywhere, which might sound terrifying. After all, there are tons of items that could be on this list but aren't (hotel remote controls are reportedly disgusting). But clearly, we're not all sick all the time. We don't always get sick when we come into contact with pathogens. It depends on the specific bacteria or virus, whether or not it gets into our bodies, and our immune system.

And there's a lot we can do to prevent the spread of illness. Employees should feel comfortable staying home from work while sick. Remember to clean surfaces that are touched frequently or that just might be neglected regularly. Wash towels and sheets more than you think.

And of course, wash your hands.