Probiotics are one of the most commonly bought supplements, and it’s easy to see why: The microbiome affects so many aspects of our health—even things you might not expect, like vaginal health and immunity. What’s tricky is that there isn’t a one-size-fits-all brand or formula for every scenario and every person.

“The technical definition of a probiotic is a live microorganism that, when administered in adequate amounts, confers a health benefit on the host,” says Andrea Nazarenko, PhD, a research psychologist and the international best-selling author of the book, When Food Hurts.  However, the best probiotic cocktail for you depends on what good bacteria your body specifically needs more of. While you can go the gut-testing route for a super nitty-gritty rec, you could also start by turning to your body for clues. Do you have a lot of digestive problems? Are you getting sick a lot? Have you been feeling depressed?

Thryve Inside CEO Richard Lin has devoted his professional life to learning more about the microbiome’s ins and outs. His company creates personalized probiotic plans, and through his research and others, he’s come to recognize some strong patterns in how different bacteria strains serve different, specific purposes.

“Often, people just look for a probiotic that [advertises] the most bacteria strains and CFUs, which is the number of bacteria per serving, but a lot doesn’t always mean better,” he says. He says that learning how to look for specific strains that will benefit your body is more important.

Because a lot of the names can look like someone forgot to take the “lorem ipsum” placeholder copy off the label, consider this your handy-dandy cheat sheet to pull up while you’re shopping. Outlined here are the main pros and cons of probiotics, per expert insight.

Probiotic benefits

1. For Constipation, diarrhea, and IBS

“The first thing people need to be aware of is the difference between the species of a bacteria and strains of a bacteria,” Lin says. “A species is the upper level of a specific type of bacteria.” Pro tip: The species is written before the strain, which is usually indicated by a letter-number combo.

Digestive issues are the major reason so many people turn to probiotics. According to clinical trials and medical research, Lin says lactobacillus plantarum and bifidobacterium lactic fermentum are great species to keep an eye out for if GI problems are why you’re reaching for a supplement.

2.  For immunity

If you have bad allergies or tend to get sick a lot, you can biohack your body by upping the count of specific bacteria strains that will help protect you from whatever bug is flying around the office in any given week: Lactobacillus rhamnosus GG, lactobacillus acidophilus L-92, bifidobacterium longum BB536, and lactobacillus paracasei LP-33 are all strains Dr. Christina Tsai, PhD, Thryve Inside’s head of research and development, recommends.

“How they help is by reducing the levels of antibodies—which can cause an allergic reaction or sickness—and strengthening your [disease-fighting] T-cells,” Lin explains. On the species level, he says to look for bifidobacterium lactic fermentum, recommended above for digestive health. It pulls double duty, keeping your immune system strong, too.

3. For vaginal health

Yeast infections are caused by out-of-whack bacteria levels, so it makes sense that if you’re prone to them, a probiotic can help. “Certain probiotic strains can stop the growth of pathogens by producing lactic acid to lower the pH, which may provide a difficult environment for pathogens to grow,” Tsai explains. “They can also produce antimicrobial substances…to kill pathogens.”

The ones that have strong scientific evidence linked to improving women’s health: lactobacillus rhamnousus GR-1, lactobacillus reuteri RC-14, lactobacillus acidophilus KS400, and lactobacillus casei rhamnosus Lcr35.

4. For depression and anxiety

While filling your meals with mood-boosting foods can help with depression, a probiotic can help provide additional support. “There are several probiotic strains that can produce GABA—a neurotransmitter involved in regulating many physiological and psychological processes in certain brain regions—and lower the stress-induced hormone corticosterone,” Tsai says. “In addition, some exert effects on the body’s stress response system and decrease stress and anxiety-like symptoms.”

Her mood-regulating picks: lactobacillus plantarum PS128, lactobacillus helveticus R0052, and bifidobacterium longum R0175.

5. For oral care

While biome-specific probiotics are on the rise, there’s some evidence that probiotics might have oral health benefits. A 2017 literature review published in Current Oral Health Reports suggests that when coupled with conventional dental health practices (like brushing and flossing), probiotics can help improve periodontal disease.  “Nasty bugs that can cause cavities, plaque, gingivitis, and bad breath are naturally present in our mouths, and probiotics can keep them in check,” says Michael P. Rogowski, PhD, senior nutrition scientist at Plexus Worldwide.

Again, the long gibberish-sounding names can be overwhelming, which is why it might be a good idea to bookmark this page and pull it up when you’re doing your probiotic shopping. But Lin says it’s a major positive that there are so many different formulations out there. “I think as we are getting closer to really personalized, targeted medicine, we’re going to start seeing a lot of different formulas for each person,” he says.

A few things to consider before taking probiotics

Probiotics are generally considered safe, the National Center for Complementary and Integrative Health (NCCIH) says; however, there haven’t been extensive studies on the frequency and severity of side effects. Additionally, people with severe illness or compromised immune systems are at greater risk for harmful side effects.

The NCCIH says that, while unlikely, probiotics can cause a slew of unwanted symptoms, including “infections, production of harmful substances by the probiotic microorganisms, and transfer of antibiotic resistance genes from probiotic microorganisms to other microorganisms in the digestive tract.” Additionally, most probiotics are considered dietary supplements, which means the FDA does not regulate them.

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