Probiotics are friendly bacteria with established health benefits. These "good" bacterial strains can be isolated from human digestive tracts, but certainly not all of the hundreds of strains found there are healthful. In fact, some are potentially harmful. And these good bacteria originally came from breast milk and other dietary sources. A product with a combination of unidentified "human" baterial strains may not offer its intended benefits. That's why it's important to look for products that contain specific strains of bacteria that have research-demonstrated benefits in supporting human health.