According to Wikipedia, handshaking was practiced as long ago as the 5th century BCE. That's 25 centuries of passing germs around by hand.
People did wash their hands in ancient times. Some religious rituals included hand washing, but its general acceptance varied throughout time and between societies. Its likely most people did not realize that clean hands are important to good health -- at least not until the mid-19th century. At that time, Oliver Wendell Holmes in the United States and Ignaz Semmelweis in Europe theorized that fevers after childbirth were transmitted by physicians dirty hands and proposed hand washing well before germs were discovered.
In the 21st century, hand washing is the foundation of infection control in health care institutions. Proper attention to hand hygiene can prevent infected wounds, serious intestinal infections, and the spread of antibiotic resistant bacteria.
Outside the medical setting, hand washing also is important. Most colds start when we pick up a virus on our hands and place it into our respiratory tracts by touching our nose, eyes or mouth. Shaking hands is one way to get the virus, but touching door handles and other objects touched by people who are ill can put the virus on our own hands.
In the kitchen, we pick up bacteria from raw meat or fish. Even if we cook the meat properly, we can contaminate other food if we do not clean our hands after handling uncooked meat or fish.
Even if we wash our hands after using the toilet, you can be sure that many others do not. Whatever they touch could become contaminated with intestinal bacteria or viruses that we could contract.
Infection enters our bodies at any opening -- our nose, mouth, eyes as already noted and even through tiny breaks in the skin. Working in the yard or at any job that is associated with getting ones hand dirty is fine. If your skin is intact, you are not preparing food or touching other people and you keep your hands away from your face, its OK to have dirty hands while working. But there are times when clean hands are necessary.
You should be sure to wash your hands before and after preparing or eating food; after using the toilet or helping a child or anyone with diapers or toileting; before and after working with someone who is ill; after a cough, sneeze or blowing the nose; after handling garbage, animal waste or soil; before and after taking care of a wound. Soap and water work great -- take 20 seconds to rub your hands vigorously working up a lather. Twenty seconds is just about how long it takes to sing the birthday song twice. If soap and water are not available and there is no visible dirt on your hands, hand-sanitizing gel is fine. Rub a small amount into your hands and fingers until it evaporates. The gel kills germs; soap and water wash them away. Hot water is not necessary. Water hot enough to kill germs would burn the skin.
Frequent washing and sanitizing could dry our skin, so a little moisturizing cream is fine after cleaning up. It doesnt take long to develop the habit of clean hands. Its good for us and its good for all of those around us.