The front doorknob, the staircase banister, the microwave door. What do these three areas have in common? They're in your home, you touch them every day, and they're likely infested with microorganisms. Or, in layman's terms, germs.

By nature, germs spread through the air, but they can linger on surfaces for 2 hours or longer. And though they're preventable through a few simple measures (covering your mouth when you sneeze or cough; washing your hands with soap and warm water for 15-20 seconds), they're plaguing Americans, especially children. According to the Centers for Disease Control & Prevention (CDC), nearly 22 million school days are lost annually to the common cold. One way to prevent sickness is to know where you're most likely to pick up germs. And with that, we give you the five germiest spots in your home.

Food preparation areas. Cutting boards and countertops are some of the worst offenders. Infectious bacteria thrive in raw or uncooked foods. To combat germs, clean and disinfect these areas immediately after preparation, making sure to gather crumbs and wipe away spilled liquids.

The fridge. If you think it's OK to store all foods together, think again. The CDC says that meat, seafood, poultry, and eggs should be separated in sealed containers and cannot have their juices dripped onto other foods. Just because it's cooling in the fridge doesn't mean it's clean.

Your toothbrush. Germs live comfortably in the bathroom-in the sink drain, in the showerhead, on the toilet seat-but it's your toothbrush that is especially dangerous. It comes into contact with one of the germiest places in the world (the mouth), and can therefore become contaminated with bacteria, blood, saliva, oral debris, and toothpaste. The CDC suggests rinsing your toothbrush thoroughly with tap water and then storing it in an open space.

Carpets. It's more than just being walked over with dirty shoes all day; carpets are filled with dust mites, perhaps the most common cause of perennial allergic rhinitis, according to the National Institutes of Health (NIH). Unfortunately, carpet dust is impossible to control. Unless your vacuum has a special HEPA (high-efficiency particulate air) filter, it will not collect dust but redistribute it into the air.

Pets. Playing with the household pet may seem fun and harmless. But when researchers study allergen levels in the home, they find that the major allergens are contained in the proteins of an animal's saliva. Next time your dog licks you, be sure to wash your hands. A lot.