Our hands travel all over the place: We use them to greet friends and to steady ourselves in trains and buses, to hold railings that thousands of others have touched before us, to eat and open doors. And in doing so, we collect thousands of germs.

Not all germs are equally dangerous. A healthy person would need to ingest about 1,000 salmonellae bacteria before getting sick. Salmonellae are common in spoiled eggs. Legionella are much more dangerous: Less than 100 of them are enough. Those bacteria love the cozy humid climate of warm-water tanks and showers. Even perfectly clean air contains thousands of mold spores and bacteria.

One square inch of toilet seat contains less than 60 germs. That means the toilet is one of the cleanest areas of all. Even some windows contain more germs and fungus spores. This is largely because toilets are cleaned several times a week. A window may be only twice a year.

Your workplace looks much worse. The average desk surface contains over 18,000 germs per square inch - 400 times more than the toilet. The highest contamination can be found on computer keyboards. There, filth gets in between and under the keys. More than 60,000 germs per square inch is no rarity.

Coins and bills change hands often, and New York researchers have identified more than 3,000 genetically different germs on dollar bills. Using sensitive detection methods, scientists can also usually find traces of cocaine on almost all bills in circulation - because some have been used for snorting. Just one more reason why vendors should never touch money and food in succession.

Even a supposedly "clean" refrigerator contains huge amounts of germs. The humid climate and the presence of fat and sugar are the ideal breeding grounds for molds of all kinds. Even when the owners clean the refrigerator diligently, the spores will eventually find their niches - like inside and behind the rubber insulation of the door.

Hospital personnel must pay attention to hand hygiene more than most. The spread of resistant bacteria can prove fatal. That's why in many hospitals there are dispensers for antibacterial solution in addition to soap and water. Before visiting a patient, disinfect your hands!

Methicillin-resistant Staphylococcus aureus (MRSA) is the name of this highly dangerous bacteria. Known antibiotics can not kill it. Even without nutrition, the germ can survive for up to seven months - on floors, tables, beds, the skin and of course on door handles.

A clinic in Harburg, Germany has now begun a promising experiment to reduce the amount of germs on door handles. Bacteria don't like copper. The number of germs shrunk by half following the introduction of the new handles. But this is no substitute for washing your hands. After all, there are still enough germs left behind.

Should we now stop shaking hands? In hospitals that may be a good idea. But in normal circumstances it may seem weird. It's probably better to simply use a good amount of common sense and hygiene: Wash your hands regularly, clean your keyboard and mouse frequently. Don't touch food right after paying for it, and clean your refrigerator from time to time.

The practice of hand-shaking has been around for more than 2,000 years. It was documented in the times of antiquity, as portrayed on this ancient Greek flask. But the ancient Greeks, who thought illness was related to a imbalance of humors in the body and represented punishment from the gods, never made a connection between hand-shaking and disease.

Hand-shaking is believed to originate in how, for two strangers meeting for the first time, approaching each other with open right hands demonstrates a lack of weapons. On a neurochemical level, a proper handshake can release chemicals in the brain including the bonding hormone oxytocin, which can promote harmony and friendship. But researchers have found it's a significant way to spread disease.

Not only does hand-shaking pass along germs, it carries unspoken meaning - yet this can vary by culture. A firm handshake is positively perceived to show decisiveness in Western societies, while Eastern societies generally prefer weaker or "limp" handshakes to prevent imparting a sense of dominance. Regardless, whenever you shake hands, you come away with more than just a lasting impression.

Hand-shaking can transmit viruses like the cold or flu, parasites like scabies, and bacteria such as Staphylococcus (pictured above). Someone who has a cold could wipe their dripping nose, leaving mucus teeming with rhinovirus on that person's hand. When you shake hands with them and then touch your eye, you can catch that infection. Still eager to shake hands?

One surefire way to prevent the spread of disease, including through handshakes, is to wash your hands with warm water and soap on a regular basis. But many people simply don't bother: In one observational study, only two-thirds of men washed their hands after using a public restroom. Which might make you ask yourself: Do I actually want to shake hands with the next stranger I meet?

Prominent figures - including Bill Gates and Donald Trump - reportedly simply do not shake hands due to the disease factor. A person who is hand-shaking phobic could always carry around a small bottle of hand-sanitizer and constantly use it. But that person runs the risk of seeming obsessive and strange. Although there are some proposals for alternatives to shaking hands …

A recent study proposed banning handshakes from healthcare settings altogether. Hospitals could be made into handshake-free zones, for example. As more people come to understand the link between the handshake and the spread of disease, the "anti-handshake" movement even seems to be gaining momentum. But what could replace the glorious gesture?

A study has shown that exchanging greetings via fist bump, or a brief touch between the outer portions of two fists, transmits 90 percent fewer infectious organisms than the handshake. And with people like Barack and Michelle Obama setting the example, perhaps that could become the next big thing.