They’re literally everywhere. Inside the bodies and on the skin of all living creatures — including us — in the water and soil, in the food we eat, and on pretty much every surface. The world is literally full of germs!

You’d never know it by looking, though, because they’re invisible to the naked human eye. But just look through a microscope — you’d be amazed.

Many germs can live right inside and on us and never hurt us because our immune systems fight off their effects. But sometimes, for very young, very old, or already sick people whose immune systems are weakened, they can cause disease that can range from mild and temporary symptoms to debilitating and life-threatening infection.

Inside and On Our Bodies

We are crawling with friendly microorganisms, mostly bacteria and some yeasts, called ("normal flora"), which live on our skin, in the lining of our nose, and in the digestive tract—the "surfaces" of the body. Normal flora like e. coli, for example, help us to break down and use the nutrition in our food.

These microorganisms normally keep each other in balance so that we stay healthy. At times, however, any of them can begin to grow out of control to cause a sickening infection.

Areas of the body such as the brain, circulatory system, and lungs—inside the body— are intended to remain sterile. When flora make their way into these areas, through a cut in the skin, for instance, they stop being friendly and cause infection that can have symptoms that range from mildly uncomfortable to life-threatening.

In Our Food and Water

Our food and water are loaded with microbes in all categories, and the sources for them are endless. Vegetables grow in soil alive with fungi and bacteria; meat is a magnet for bacteria; shelf stockers and customers at the grocery who have touched our food have transferred microbes on their skin to it, and we do the same when we prepare it; and anything but treated municipal water is likely to contain bacteria and viruses galore from animals that have been in the water, and from farmland runoff.

It's important that food and water be kept cool enough to prevent the growth of microbes and cooked to the right temperature or otherwise purified to kill the microbes before they're consumed.

In Our Homes

Because we are hosts to microbes, we transfer them to everything we touch, sneeze on, and cough around. Our kitchens, being headquarters to microbe-loaded food preparation, is especially teeming, particularly if we leave food out or don't clean food preparation areas well. Our pets also carry and transfer microbes into our homes through their close contact with all kinds of organic material outside. And, of course, the bathroom is one of the most inviting places for bacteria to hang out.

In Public Places

Wherever you find lots of people, you'll find lots of germs. Contagious or infectious diseases are transmitted through the air, on surfaces, or in food when sick people cough, sneeze, or don't wash their hands after using the bathroom. So, places like offices, schools, gyms, restaurants, and public transportation terminals are places to be especially careful.