No matter where you are, or what you're doing, you are never alone. Everywhere you go trillions of tiny friends accompany you.
Yep, I'm talking about microbes - brilliant bacteria, fascinating fungi and amazing archaea.
For many people the mention of bacteria sends a bit of a shiver down the spine. It's understandable - from a young age we're taught that "germs" are bad. That we need to be on constant high alert, and disinfect everything.
But microbes, or at least most of them, are not our enemy. In fact, they can be our good friends.
Your body is crawling with microbes. They outnumber your human cells by about 10 to 1. They are all over your skin. In your eyes. In your mouth. They even live in your digestive tract.
The microbes that live in our digestive tract, known as our gut microbiome, have been an increasingly hot topic for research over the last few years. For a while now we've understood that the gut microbiome plays a role in digestion.
Certain types of bacteria help us to digest different sugars or fibre, helping us access nutrients. For example, in babies, the bacteria known as Bifidobacteria can help digest the sugars in breast milk. It also makes sense that our gut microbiome may play a role in intestinal diseases. The symptoms of irritable bowel syndrome, for example, have been linked to the types of microbes living in the gut.
Now we are also starting to see evidence that the gut microbiome influences a range of other things - from our weight, to our immune system function, to our mental health. The link between microbes living in our guts and mental health is particularly interesting.
Some of the bacteria that inhabit our digestive system can produce neurotransmitters, or the building blocks of neurotransmitters, including dopamine and serotonin.
Imbalances in these "brain chemicals" have often been linked to mental health issues like depression. So the bacteria living in our guts might just influence our brain function.
Our gut microbiome is not set in stone. It can change over time. Things like medications will affect our microbial communities, as will our diet.
In general, gut microbiome studies suggest that the more diverse our microbiome is the better. That is, the greater variety of microbial species, the healthier we are.
So how can we help support this microbial diversity?
Eating a wide variety of foods, particularly fresh fruit and high-fibre vegetables is a good start. As is choosing foods that are rich in compounds called polyphenols - including nuts and whole grains, olive oil and berries (and red wine and dark chocolate - woohoo!). Fermented foods might also help, as will taking antibiotics only when necessary.
Take a few simple steps to look after your trillions of tiny friends, and they'll help look after you!