But it's more than that.
Hand washing has been shown to be one of the most effective ways to stay healthy.
Why the fuss? Because after you've touched something contaminated with viruses or bacteria, your hands give germs a free ride into your body through your eyes, nose or mouth, according to the U.S. Centers for Disease Control and Prevention.
Learn more about hand washing from the experts:
Why is it so important to wash your hands?
Simply put, washing your hands frequently and thoroughly helps keep you healthy.
"You use your hands to touch everything around you, and it's the fastest way to communicate infectious germs," said Kevin Morano, a professor in the department of microbiology and molecular genetics at the University of Texas Medical School at Houston. Some common illnesses that can be transmitted via the hands include the flu, the common cold and a number of diarrheal illnesses. Remember that last stomach bug you had? You probably got it from your hands.
Regular washing of hands with soap and water could reduce deaths from diarrheal illnesses by 50 percent, according to CDC estimates.
How can you catch a cold by not washing your hands?
Germs may live on inanimate objects for an extended time. If you touch contaminated surfaces, the germs get on your hands. Eventually, you touch your eyes, nose or mouth, which gives germs access to your insides.
"The top of the list is the restroom, and everything associated with the restroom," said Morano. Things like computer keyboards, phones and TV remotes may have some germs on them, he said, but most bacteria and viruses prefer warm, wet environments, like a hand towel in the bathroom.
What's the right way to wash your hands?
"The proper way to wash your hands is with lots of soap and warm water for as long as you have the patience for, but aim for at least 20 to 30 seconds," Morano said. "If you can sing the 'Happy Birthday' song twice, you've washed long enough."
What about the fingernails? Is it necessary to use a nail brush?
Alison Pittman, a nurse and assistant professor at the College of Nursing at Texas A&M Health Sciences Center in Bryan, said you don't need a special brush to clean under your fingernails. Just be sure to get the soap and water under your nails, she advised.
Does water temperature matter?
No, said Morano. But, if you use water that's too hot, you probably won't wash long enough. It's more important to use soap for a longer period of time.
Do you need to use antibacterial soap?
"Soap and water are a good solution for dirty hands," Pittman said. "Any soap has ingredients that break the cells of the bacteria, killing them." And, if there's no soap or water available, "use an alcohol-based sanitizer that's at least 60 percent alcohol -- although these products aren't as effective if hands are visibly soiled," she said.
Do some soaps clean better than others? Should they contain specific ingredients?
Any soap will do, said Pittman.
Does a quick rinse do anything for your hands?
A quick rinse won't clean your hands. Rather, Morano said, washing for a while with soap is what gets your hands clean.
Isn't exposure to some bacteria supposed to be good for you, because it builds up resistance?
"Exposure to small amounts of germs is probably good for you, but it's unsafe to play with a jar of salmonella," Morano said. "That dose is higher than the body can deal with."
What Morano means is that no one needs to go out of their way to be exposed to germs. Everyone encounters a significant number of microbes throughout the day, and the immune system is constantly being challenged. As he said, you don't need to add to the challenge by not washing your hands.
Do hands need to be washed after gardening?
The CDC recommends washing your hands after gardening, even if you were wearing gloves, because there are bacteria and parasites in some areas of soil.
Can you get sick from touching a pet?
Morano said that you probably can't get sick by touching your pet, but if you touch your sick pet and then don't wash up before touching another pet, you could transfer germs to that pet and it could get sick.
Can you wash your hands too much?
Not really, said Pittman. But, if you're in a job like nursing where you have to wash your hands many, many times a day, your skin can get dried out and may even crack, she said. And Morano added that a crack in the skin is "like a microbe freeway" -- it gives germs direct access into your body from your hands.
To counteract this, Pittman recommended using moisturizing soap and also applying moisturizing lotion repeatedly throughout the day. "It's OK to put lotion on after you wash your hands, but you still need to wash your hands at the recommended times," she said.
Both experts said that it's crucial to wash your hands any time you use the bathroom and definitely before you start cooking or doing any kind of food preparation. Washing hands during food preparation is particularly important when you're working with raw meat, poultry or eggs. If you're taking care of someone who's sick, be sure to wash your hands more than you normally would, and wash your hands after you change a diaper, said Pittman. Whenever you're sick, wash your hands after you sneeze or cough into your hands. And wash your hands after you take out the garbage, she said. Also wash, your hands after feeding pets or giving them treats, as well as after you clean up pet waste.
"Don't be shy about asking anyone taking care of you or a loved one if they've washed their hands," Pittman said, noting that this includes doctors and other health-care providers.
The U.S. Centers for Disease Control and Prevention has more on hand washing.
And meet Henry the Hand, an Ohio doctor's cartoon companion who helps teach kids the benefits of hand hygiene.