Lactobacillus is simply dried bacteria that occur naturally in unpasteurized whole milk. The bacteria is harmless. The human colon normally contains over 400 different bacteria which provide many health benefits. Very occasionally, a bad bacteria may show up and cause health problems. The purpose of this bacteria is to replace the bad bacteria with a gentle harmless one. The FDA regards this product as a food supplement. It has never been proven scientifically to be a benefit in any health condition. Still, some physicians will use it when a GI infection or diarrhea occurs in the hope that a change in the colon bacteria will help.