Probiotics have been receiving an increasing amount of attention from the general public in recent years. The dietary supplement market has been increasing in value around the world. However, there is a general lack of understanding of the underlying mechanisms of actions that probiotics take inside the human body. Microbiota in human bodies depend on unique personal characteristics like diet, age, geographical location, and gender, and there are no bacteria species that are present in all humans. Numerous researches have been carried out to identify the most abundant bacterial species and their association with biological and environmental factors. Probiotics have been experimentally proven to assist in treating a number of human conditions as well as alleviating the symptoms of others. The mechanisms of their action are not limited to the inhibition of pathogenic activity but they also have immunomodulatory anti-inflammatory effects. However, some concerns have been raised by the members of the scientific community. The regulation of the production of probiotics requires some further revisions.