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Lactobacilli are the protective bacteria that keep a healthy vagina healthy. They feed on sugars in the vaginal lining and produce lactic acid, which keeps the vagina slightly acidic and crowds out the disruptive bacteria behind problems like bacterial vaginosis. Keep your lactobacilli thriving and a lot of common vaginal trouble simply never gets a foothold.
A whole family of these bacteria exists, but only a handful set up home in the vagina. Lactobacillus (once known as Doderlein’s bacillus) is the group most vaginas rely on, and it is the one we spend most of our time helping people rebuild.
What lactobacilli do for your vagina
Lactobacilli are named for lactic acid: they turn sugars into it, and that acid holds the vagina at a low pH of roughly 3.8 to 4.5, which most disruptive bacteria can’t tolerate.1 That single trick does a lot of the heavy lifting for vaginal health.
They have a few other tools as well. Some strains make hydrogen peroxide, many produce bacteriocins (natural antibacterial compounds that target other bacteria), and they physically compete for space and food so there’s less room for anything unwelcome to move in.1
A lactobacillus-dominant vagina is also associated with a lower risk of picking up some sexually transmitted infections. That’s a real association, but it isn’t armour: it doesn’t reliably protect against HIV or other STIs, so it’s no substitute for condoms, testing and the usual sensible care.
The key vaginal lactobacilli
Most vaginas are dominated by one of just four species: Lactobacillus crispatus, Lactobacillus iners, Lactobacillus gasseri or Lactobacillus jensenii.2 Which one you have makes a real difference.
L. crispatus is the gold standard. A crispatus-dominant vagina tends to be the most stable and the most resistant to BV and other imbalances, which is why a healthy vaginal microbiome is usually a crispatus-rich one.2
L. iners is the exception that proves the rule. It’s a lactobacillus, but a fragile, fair-weather one that often hangs around while the microbiome is shifting towards or away from BV, so an iners-dominant result is less protective than a crispatus one.2
When lactobacilli are lost
When the protective lactobacilli are knocked back, the pH climbs and disruptive bacteria move in, which is the basic story behind BV and aerobic vaginitis. Antibiotics, harsh washes, semen, hormonal shifts and simple bad luck can all trigger it.
A good functional approach treats this as two jobs. Clearing the disruptive bacteria is only half of it; the other half is getting the protective lactobacilli re-established so the improvement actually holds. There’s solid trial evidence that lactobacillus probiotics, taken orally or vaginally, can help restore the vaginal flora and ease symptomatic BV.3–4
The most useful first step is knowing what you’re actually working with. A comprehensive vaginal microbiome test shows which lactobacilli you have (or don’t), so any rebuilding can be matched to your own picture rather than guessed at.
In our clinic, recurrent BV tends to settle for good once the focus shifts to rebuilding the protective lactobacilli and the terrain they need to thrive. Our free Killing BV guides walk through that whole approach, and you can book an appointment if you’d like a plan matched to your results.
Lactobacilli beyond the vagina
The same family does a lot of work outside the body, too. Lactobacilli drive the fermentation of foods like sourdough, yoghurt, cheese, kefir, sauerkraut, kimchi, pickles and kombucha, where the lactic acid they produce is what gives these foods their sour tang. They also live, in smaller numbers, in the gut.
A note on the names: the 2020 reclassification
If you go looking for lactobacillus species, the names can be confusing, and there’s a good reason. In 2020, a major genetic review split the sprawling old genus Lactobacillus into 25 separate genera, because the species lumped under one name turned out to be far more different from each other than their shared label suggested.5
Happily for vaginal health, the key vaginal species kept the Lactobacillus name. L. crispatus, L. gasseri, L. jensenii and L. iners are all still lactobacilli. Many familiar probiotic and food species were renamed, though, so, for example, L. plantarum is now Lactiplantibacillus plantarum, L. rhamnosus is now Lacticaseibacillus rhamnosus, and L. reuteri is now Limosilactobacillus reuteri.
The former lactobacilli, by their current genus
Here are the species once grouped together as Lactobacillus, sorted into the genera they now belong to after the 2020 update.5 The key vaginal species sit in the first group.
- Lactobacillus (the emended genus, kept for the host-adapted species, including the key vaginal ones): acidophilus, acetotolerans, amylolyticus, amylovorus, apodemi, crispatus, delbrueckii, fornicalis, gallinarum, gasseri, gastricus, hamsteri, hayakitensis, helveticus, iners, intestinalis, jensenii, johnsonii, kalixensis, kefiranofaciens, kitasatonis, psittaci, rogosae, ultunensis
- Lacticaseibacillus (the casei group, widely used as probiotics): casei, paracasei, rhamnosus, zeae, sharpeae, pantheris, thailandensis
- Lactiplantibacillus (plant-associated): plantarum, pentosus, paraplantarum, manihotivorans
- Limosilactobacillus (gut- and host-associated, including several vaginal species): fermentum, reuteri, mucosae, oris, vaginalis, panis, pontis, antri, coleohominis, ingluviei, frumenti, secaliphilus, equigenerosi
- Ligilactobacillus (host-adapted): salivarius, animalis, murinus, ruminis, agilis, aviarius, saerimneri, ceti, equi, acidipiscis
- Levilactobacillus (dough and fermentation): brevis, parabrevis, hammesii, namurensis, spicheri, acidifarinae, zymae
- Lentilactobacillus (slow-growing fermenters): buchneri, parabuchneri, hilgardii, kefiri, parakefiri, diolivorans, farraginis, parafarraginis
- Companilactobacillus (cereal, vegetable and meat fermentations): alimentarius, farciminis, mindensis, crustorum, versmoldensis, paralimentarius, nantensis, kimchii
- Latilactobacillus (meat and food fermentation): sakei, curvatus, graminis, fuchuensis
- Fructilactobacillus (fructose-loving): fructivorans, sanfranciscensis, lindneri, homohiochii
- Secundilactobacillus (fermentation): collinoides, paracollinoides, malefermentans
- Liquorilactobacillus (from liquids and drinks): mali, nagelii, satsumensis, vini, ghanensis
- Loigolactobacillus (food-associated): coryniformis, bifermentans, rennini
- Schleiferilactobacillus (fermentation): perolens, harbinensis, camelliae
- Paucilactobacillus (ferment few sugars): vaccinostercus, suebicus, oligofermentans
- Furfurilactobacillus (from bran): rossiae, siliginis
- Amylolactobacillus (starch-degrading): amylophilus, amylotrophicus
- Lapidilactobacillus (environmental): concavus, dextrinicus
- Apilactobacillus (from bees): kunkeei
- Agrilactobacillus (from fields): composti
- Dellaglioa (cold-tolerant): algida
Three species that used to sit on this list have since been moved out of the lactobacillus family altogether and are no longer considered lactobacilli: L. catenaformis (now Eggerthia catenaformis), L. vitulinus (now Kandleria vitulina) and L. rimae (now placed in Atopobium/Lancefieldella).
Frequently asked questions
Which lactobacillus is best for the vagina?
Lactobacillus crispatus. A crispatus-dominant microbiome is the most stable and protective, so it’s what we’re aiming to re-establish when we help someone rebuild after recurrent BV or vaginitis.2
How do you increase lactobacillus in the vagina?
A few things help. Oral and vaginal lactobacillus probiotics can lift your numbers, with the best evidence when you’re recovering from an imbalance like BV.3–4 Beyond that, it’s mostly about protecting the ones you already have: skip the douches and harsh ‘feminine’ washes, don’t reach for antibiotics you don’t need, and treat any active dysbiosis so the protective species can move back in. Testing first shows which lactobacilli you’re starting with, so you can rebuild to a plan rather than guess.
Are lactobacillus probiotics worth taking for vaginal health?
They can help, especially alongside clearing an active imbalance, with trial evidence that oral and vaginal lactobacilli support recovery from symptomatic BV.3–4 They work best matched to your own microbiome rather than taken blindly, which is why testing is worth doing.
Do lactobacilli protect against STIs?
A lactobacillus-dominant vagina is linked with a lower risk of acquiring some infections, but it’s an association, not reliable protection. It doesn’t guard against HIV or other STIs on its own, so keep using condoms and regular testing.
This is general information, not a substitute for personalised medical advice.
- Chee WJY, Chew SY, Than LTL. Vaginal microbiota and the potential of Lactobacillus derivatives in maintaining vaginal health. Microb Cell Fact. 2020;19(1):203.
- Ravel J, Gajer P, Abdo Z, et al. Vaginal microbiome of reproductive-age women. Proc Natl Acad Sci U S A. 2011;108(Suppl 1):4680–4687.
- Reznichenko H, Henyk N, Maliuk V, et al. Oral intake of lactobacilli can be helpful in symptomatic bacterial vaginosis: a randomized clinical study. J Low Genit Tract Dis. 2020;24(3):284–289.
- Mei Z, Li D. The role of probiotics in vaginal health. Front Cell Infect Microbiol. 2022;12:963868.
- Zheng J, Wittouck S, Salvetti E, et al. A taxonomic note on the genus Lactobacillus: description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae. Int J Syst Evol Microbiol. 2020;70(4):2782–2858.
