The colon is where the majority of probiotics are found, but there are billions more in our mouths, oral cavities, nasal cavities, oesophaguses, gums, and pockets of our pleural cavity (surrounding our lungs). They reside in our rectum, vagina, gastrointestinal tract, and stomach. inside of joints, armpits, toenails, between toes, urinary tract, inside our urinary tract, and several more locations!