Humans and bacteria have a curious relationship.

On the one hand, some species of bacteria are responsible for some of the most nefarious of human diseases.

On the other hand, many species have peacefully coevolved with humans for hundreds of thousands of years to play essential roles in digestion and in bolstering the immune system.

Your body is constantly teeming with these organisms, which collectively make up the human microbiome.

James Archer/ CDC No two people house the exact same microbial mix, there are a few species that are almost always found in all humans.

Here are 13 microbes that are very likely living on or inside of you at this very moment, and whether or not each can cause illness.