So, you're dealing with a vaginal yeast infection (again)? That sucks, and you'll want to do whatever you can to clear it up as soon as possible — nobody wants to deal with all that itching, redness, soreness, and nasty vaginal discharge a second longer than they have to!
Whether you're considering yeast infection treatment at home as a stand-alone or in combination with over-the-counter antifungal medications, you will hear a lot about probiotics. Some people will advise you to take oral Lactobacillus supplements, while others will swear that douching with yogurt cures yeast infections.
First Things First: What Are Probiotics, Anyway?
The term "probiotics" is used to refer to ingestible living microorganisms that are meant to benefit your health in some way . These beneficial microorganisms naturally appear in some foods, such as yogurt and kimchi (fermented cabbage), but they are also sold as probiotic supplements or creams. You may additionally come across the term "prebiotics", which refers to substances that encourage the growth of beneficial bacteria rather than ingesting bacteria directly. "Synbiotics" combine probiotics and prebiotics.
Examples of probiotics include:
- Lactobacillus species
- Streptococcus thermophilus
- Saccharomyces boulardii 
Why Do People Suggest You Use Probiotics For Vaginal Candidiasis?
Simply said, because bacteria play an essential role in maintaining a healthy vagina.
The normal, healthy, vaginal microbiome is made up of over 50 different species of microorganisms, with Lactobacillus species being dominant in healthy vaginas. The vaginal flora can undergo rapid changes with hormonal fluctuations, blood sugar level changes, and alterations in vaginal pH levels. 
Vaginal candidiasis, or a vaginal yeast infection, is defined as the symptomatic overgrowth of yeast species.  Vaginal yeast infections are almost always caused by Candida albicans, but other species can be responsible as well .
If yeast gets the opportunity to proliferate because other species of microorganisms have been disturbed — something that often happens after a course of antibiotics, for example  — it makes all the sense in the world that "feeding" your body good bacteria would prevent or cure vaginal candidiasis. Does it work, though?
Do Probiotics Prevent Yeast Infections? Do They Help Treat Vaginal Candidiasis?
Some studies have found that Candida overgrowths are indeed associated with either a low number of Lactobacillus bacteria in the vagina, or with H2O2-non-producing vaginal Lactobacilli. There is also research to suggest that Lactobacilli actively inhibit the growth of Candida species or interfere with their sticking to vaginal cells, thereby preventing yeast infections.  Other research shows that Lactobacilli are still abundant in women with vaginal candidiasis, however, contradicting these findings. 
There is some evidence that probiotics do make a difference in conjunction with conventional antifungal medication. One study found that women with vaginal candidiasis who took the popular antifungal yeast infection treatment fluconazole were more likely to successfully be cured of their yeast infections if they also used the probiotics Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 once a day for four weeks.  Candida albicans apparently loses its metabolic activity and eventually dies off in the presence of these probiotics .
Probiotics made a particular difference to women who suffered from recurrent yeast infections — 80 percent of the recurrent yeast infection patients who used a placebo tested positive for yeast after the treatment period, compared to only 18.2 percent of the probiotic group! 
Another study showed that vaginal capsules containing the probiotics L gasseri LN40, Lactobacillus fermentum LN99, L. casei subsp. rhamnosus LN113 and P. acidilactici LN23 were somewhat helpful in reducing the symptoms of both vaginal candidiasis and bacterial vaginosis, and that their use led to slightly fewer recurrences. 
What about probiotic yogurt, containing a live Lactobacillus acidophilus culture, then? Here, research suggests that women who consumed eight ounces of this kind of yogurt a day were less likely to be colonized by Candida albicans and other yeast species, and enjoyed a reduced risk of symptomatic vaginal yeast infections as well. 
The Bottom Line
Some studies do show that probiotic supplements, either taken orally or in the form of vaginal capsules, show promise in preventing the recurrence of vaginal yeast infections. Probiotics may also act as a really helpful addition to conventional antifungal treatments for vaginal candidiasis. The same holds true for probiotic yogurt, but not pasteurized yogurt.
Women who would like to try home remedies for yeast infections certainly have more effective methods at their disposal, including garlic, boric acid, and tea tree oil. We'd never suggest you use probiotics instead of other yeast infection treatments — there's simply not enough evidence that this works. If you are looking to use probiotics as a supportive remedy alongside other yeast infection treatment, or if you would like to use probiotics as prophylaxis to prevent future yeast infections, you don't have a lot to lose, however. The probiotics might work, but if they don't, no harm will come to you.