The problem with Kefir is the yeast present in it. Most candida sufferers react to yeast in a way or other. Try plain yogurt and see if you react to it. Some people tolerate yogurt and no kefir. Yogurt only has bacteria, kefir has bacteria and yeast. If it is the casein or the lactose, you will react to both, if not is the yeast present in kefir.