 Probiotics have become commonplace in many products we consume, like yogurt, certain drinks and supplements, because they are thought to have numerous health benefits. But to understand how exactly these products work, we first need to understand the concept of a microbiome. A microbiome is a community of microorganisms such as bacteria, fungi and even viruses that inhabit a specific environment, communicate with each other, share resources and exhibit a particular collective action based on their surroundings. Many of these communities of microorganisms exist within other organisms such as humans, but they can also exist in the world around us. Let's start with the humans first. There are multiple microbiomes within the human body, including on the skin, in the gastrointestinal tract, lungs and even the belly button. Healthy microbiomes are critical because each of these collections of microbes ensures our body functions normally. For example, the bacteria in the skin microbiome use a process called quorum sensing to communicate with each other and form a biofilm that helps defend us from harmful infections and other skin conditions. The most well-known microbiome in the human body, however, is the community of microbes that live in our digestive tracts, the gut microbiome. Here the microbes primarily help us break down the food that we eat into nutrients that can be absorbed by our body. More recently, scientists have discovered that the gut microbiome also plays critical roles from a very young age, like helping to develop the immune system. If any of these communities are disrupted or become unbalanced, it can have significant health consequences, which we see with antibiotics. While these medicines kill the bad bacteria that cause infections, they can kill the good bacteria too. In the gut, this can lead to abdominal pain, fatigue and disruption of blood sugar regulation. Probiotics, which are a collection of the good bacteria, can help restore some of the gut microbiome that is lost due to antibiotic treatment, disease or other factors. While microbiomes in the body are the most well known because of their direct impact on our health, microbiomes outside of the body are just as important. For example, there is a unique microbiome that exists around deep-sea hydrothermal vents, areas of the seafloor that spew scalding water and chemicals that would be toxic to most living organisms. This community of microbes is able to convert many of these toxic chemicals into organic materials that can be used by other organisms, keeping the ecosystem around these vents healthy. So the next time you see probiotics or your deep-sea diving, don't forget about the microbiomes that are playing a huge role in not only your health, but also that of the environment around you.