Acidophilus      
Of the many lactobacillus, a specific type of bacteria, that can inhabit the human colon, Acidophilus (Lactobacillus acidophilus) is probably the most well known.

There are many claims for acidophilus, though it is most commonly used for replacing friendly bacteria in the colon to help the recovery of bodily functions after a course of anti-biotics. In fact acidophilus is itself antibacterial, and with regular use it may even replace harmful bacteria in the colon and also in the vaginal tract of women, which is why it is commonly used to treat yeast infections, including intestinal yeast overgrowth.

These bacteria also help in the production of some B vitamins and vitamin K, and in the breakdown of various foods.

The evidence for some of the other claims for acidophilus is largly anecdotal rather than proved by research, although ongoing research at several universities looks as though it will hold up at least some of these claims. These unproven effects include: help with stomach and digestive upset; improved immunity; help with allergies (particularly food allergies); improved skin health; help with herpes infections; reduced cholesterol levels; and reduced cancer risk (especially colon cancer).