The most common problem for which people are hospitalized today is gastrointestinal ailments. No other system in the body is subject to so many problems as is the digestive system of the human body. Thus, it is no surprise that the market for pharmaceuticals, OTC's and dietary supplements is quite large when it comes to products that address GI health concerns.
The GI tract is teeming with live microorganisms, both of "friendly" and pathogenic nature. The combined sum of these bacteria are what is called "microflora", which can be adversely affected by stress, medications, diet, aging, and a variety of other factors. Probiotics are beneficial strains of bacteria that exist with the intestinal microflora that confer health benefits to the host. These health benefits include immunomodulation, fortification of the intestinal wall against invasive organisms, decreased colonization of pathogenic bacteria in the intestinal and vaginal tracts, and improved urinary tract health.

The most well known and well represented group of probiotics in the intestinal microflora are species from within the Lactobacillus and Bifidobacteria genera. Right before an infant is born, he or she is intestinally sterile (no intestinal bacteria is present). Once the child passes through the vaginal tract (or via C-section delivery), the infant immediately begins to colonize bacteria throughout the digestive tract. At this very young age, the majority of species come from the Bifidobacteria genus, with smaller amounts of Lactobacillus also present. As the infant ages, his or her microflora begins to shift to a higher percentage of Lactobacillus species, and eventually by the age of three or four years old, the child’s microflora profile resembles that of an adult.
Probiotic bacteria, or "friendly bacteria," help to protect intestinal health and integrity in a variety of ways:

Improving the health of the digestive tract by restoring the microflora to a healthy state through increased probiotic consumption can have tremendous health benefits. Various medical professionals and other healthcare authorities have seen the benefits of probiotic supplementation firsthand in the patients they serve. In addition, every day millions of consumers endorse probiotics by regularly and repeatedly purchasing probiotic dietary supplements and probiotic containing foods and beverages.
There is currently a sea change in the type of research that is being done with probiotic organisms. In the past, probiotic research was limited to looking at the benefits of probiotics for improving intestinal health. Today, researchers are investigating a wide variety of health concerns to see how probiotics may benefit these conditions. Some of the far-ranging research topics being conducted today include: