Drug resistance is a huge problem. As you can imagine, if you get a drug resistant strain of anything … as the name implies, it’s quite difficult to get rid of. If that happens to be a candida infection it can cause many problems from allergies to infertility. E. Coli infections can also be extremely problematic and occasionally a really bad strain gets into the food supply and some people die. In this study researchers found that the essential oil of rosemary was able to kill drug-resistant mutants of candida and E. coli as well as some other nasty organisms. If you are ingesting any essential oils you should be under the care of a health care practitioner that has training in herbal medicine. Fat soluble substances can bioaccumulate and become toxic so caution is necessary when taking essential oils internally. Suppositories can also be made from essential oils to treat local problems (such as vaginal yeast infections), however, recurrent yeast infections are rarely limited to the vagina. On the other hand, if you are susceptible to recurrent yeast infections, adding rosemary to your diet on a regular basis could be helpful. But you have to eat the leaves or cook them in oil in order for it to work.
 
Altern Ther Health Med. 2007 Sep-Oct;13(5):54-9.