What if germs did not exist?

Germs are so tiny that you need a microscope to see them.

Some germs can give you a cold. So what if there were no germs at all? Would that be good, or would we miss some of them?

You've probably heard grown-ups say, 'Wash your hands, there are germs!' Germs are tiny living things, called microbes, that are far too small to see without a microscope. Some can make people sick, so it's easy to think a world without any germs would be perfect.

But is that true? What if every single microbe disappeared, the harmful ones and the helpful ones? We can't make microbes vanish, and we wouldn't want to. Let's follow the clues and find out why.

Germs come in four major types: bacteria, viruses, fungi and protozoa (KidsHealth). Some cause disease. But the microbes that naturally live on and in us form the microbiome, which NIEHS describes as contributing to human health and wellness in many ways.

This thought experiment deletes all microbes and asks what the human body, and human food, would lose. It follows three threads: the gut microbiome, the immune system's relationship with microbes, and fermentation in foods. Well-supported findings are labeled as fact; projections are labeled as ideas.

Lots of tiny microbes live on your skin and inside your tummy.

Many of them are not bad germs at all. Lots are helpers!

Your body is home to a huge crowd of microbes. Scientists at the National Institute of Environmental Health Sciences say there are about as many microbes in your body as there are human cells. Your gut, skin, mouth and nose each have their own community. Scientists call this crowd your microbiome.

KidsHealth explains that not all bacteria are bad. Good bacteria live in your intestines and help you use the nutrients in your food. Your microbiome first forms in your earliest years, and it can change over your life.

The National Institute of Environmental Health Sciences (NIEHS) defines the microbiome as all the microbes, such as bacteria, fungi and viruses, and their genes, that naturally live on and in our bodies, and notes there are as many microbes as human cells in the body. Each site, gut, skin, oral and nasal cavities, has a distinct community.

A person's core microbiome forms in the first years of life and can shift with diet, medications and environmental exposures. The NIH Common Fund's Human Microbiome Project built shared research resources to characterize these communities and their roles in health and disease.

Now pretend every microbe is gone. No more colds from germs!

But the helper microbes would be gone too. Your tummy would lose its little helpers.

If every microbe vanished, germs that cause colds and sore throats would vanish too. That part sounds great. But the helpful microbes would go as well.

NIEHS says our microbes protect us against harmful germs, help our immune system develop and help us digest food to produce energy. Without them, our bodies might miss all of that help. And foods made with the help of microbes, like yogurt and many cheeses, would disappear too. These last ideas are our guesses about an imaginary world.

Removing all microbes would remove pathogens, an obvious gain. It would also remove functions the microbiome provides: NIEHS lists protection against pathogens, support for immune development and help digesting food to produce energy, and KidsHealth notes that gut bacteria help us use the nutrients in food.

Beyond the body, foods defined by microbial fermentation, such as yogurt, would no longer exist in their present form. How a human body and the wider living world would function with zero microbes is far beyond any study, so those wider consequences are ideas, not results.

Your body has a germ-fighting team. It is called the immune system.

Some of its cells can remember germs they met before. Then they fight them faster next time!

Your immune system is a network of cells, tissues and organs that work together to protect your body. White blood cells are part of the team. Some, called phagocytes, gobble up invading germs. Others, called lymphocytes, help your body remember and recognize germs it has met before.

Vaccines use that memory: they get your body extra prepared to fight certain serious illnesses. And NIEHS says the microbes that live in us help the immune system develop. So microbes and the immune system are linked from the start.

NIAID describes the immune system's overall function as preventing or limiting infection; people with weakened immunity can be infected by microbes that typically do not cause infection in healthy people. That observation shows how many microbes are harmless when the immune system is working.

White blood cells include phagocytes, which engulf invaders, and lymphocytes, which let the body remember and recognize previous invaders (KidsHealth). NIEHS adds that resident microbes help the immune system develop. In a world with no microbes, the immune system would have nothing to defend against, but also nothing to learn from; what that would mean is speculative.

Yogurt is made with helpful bacteria! They turn milk thick and tangy.

Cheese makers use helpful bacteria too.

Some of your favorite foods depend on microbes. In the United States, food rules say that yogurt must be made by adding two kinds of helpful bacteria to milk: Lactobacillus delbrueckii subspecies bulgaricus and Streptococcus thermophilus. These lactic acid bacteria turn milk into yogurt.

Cheese makers use lactic acid bacteria too. The University of Guelph's cheese-making course explains that these bacteria are added to start the cheese's fermentation, so they're called starter cultures. They are also used for foods like olives and fermented vegetables.

The U.S. standard of identity for yogurt (21 CFR 131.200) requires culturing dairy ingredients with a characterizing culture containing the lactic acid-producing bacteria Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Without these microbes, yogurt as legally defined could not exist.

In cheese, the University of Guelph's course material explains, lactic acid bacteria strains are added to start fermentation, hence the name starter cultures, and they help ensure safety and develop flavor. The same bacterial family is used for fermented meats, olives and vegetables. A microbe-free kitchen would lose a whole category of food.