Probiotics are the good bacteria that we find in our gut. One of them is well known, the acidophilus which is used to make yogurt. By taking probiotics you are ensuring that your gut has enough good bacteria. The belief is that not having enough good bacteria causes ill health. Many people are found to not have enough good bacteria and therefore get colonized with bad bacteria. My daughter and I have been tested and we were found to be in this position. Probiotics have been found to help those with allergies because they increase the health of your gut and this is where your immune system is.