Probiotics are generally considered safe for breastfeeding mothers. No published data show adverse effects in breastfed infants whose mothers take probiotic supplements, and because probiotics are rarely absorbed into the bloodstream, they are not expected to transfer into breast milk in significant amounts. A review in Canadian Family Physician concluded that probiotics pose no safety concerns for pregnant or lactating women.
Why Probiotics Don’t Reach Your Baby Through Milk
When you swallow a probiotic capsule or eat a fermented food, the bacteria work primarily in your digestive tract. They are rarely absorbed systemically, meaning they don’t enter your bloodstream in meaningful quantities and therefore aren’t expected to pass into breast milk as active supplements. This is the main reason safety concerns for nursing infants are minimal.
That said, breast milk naturally contains its own probiotic bacteria, including various Lactobacillus species. These naturally occurring microbes are one of the ways breast milk helps shape a newborn’s developing gut. The bacterial diversity in breast milk varies from mother to mother and depends on diet, environment, and other individual factors. So while your supplement likely isn’t transferring directly, your milk is already delivering beneficial bacteria on its own.
What the Research Shows for Infants
A systematic review and meta-analysis of randomized controlled trials found that maternal probiotic supplementation during breastfeeding was both safe and associated with beneficial changes in the infant gut microbiome. The review concluded that Lactobacillus, Bifidobacterium, and a few other well-studied strains can be used as maternal supplements to promote infant health. Multiple clinical trials have also given probiotics directly to newborns after delivery without any increase in adverse effects.
One area that’s gotten attention is eczema prevention. Studies have tested giving probiotics to mothers in late pregnancy and during breastfeeding, then tracking eczema in their infants. In one trial, infants of mothers receiving probiotic supplements developed significantly fewer episodes of eczema compared to a placebo group. However, the overall certainty of this evidence is still considered low, and not every trial has replicated the result. Probiotics did not appear to prevent allergic sensitization itself, only nonatopic eczema in some cases.
Side Effects for Mothers
The most common side effects of probiotics are mild digestive symptoms like gas and bloating, which typically resolve within the first few days. There’s no evidence that probiotics reduce milk supply. In fact, a large Norwegian study of over 57,000 women found the opposite: mothers who consumed probiotic milk were less likely to stop breastfeeding before four months. Women drinking probiotic milk had 21% lower odds of stopping breastfeeding entirely before four months compared to non-consumers.
The same study did find a slightly higher rate of reported breastfeeding complications in the probiotic group, including sore nipples (22% higher odds) and a modest 9% increase in mastitis visits. The researchers noted this could reflect the fact that women who consume probiotic products may also be more health-conscious and more likely to seek care for breastfeeding issues, rather than the probiotics causing problems directly. Importantly, the association with medication-treated mastitis was not significant after adjusting for other factors.
Probiotics and Mastitis
Interestingly, certain probiotic strains are being studied as a way to prevent and treat mastitis rather than cause it. A systematic review and meta-analysis found that Lactobacillus salivarius and Lactobacillus fermentum both effectively reduced bacterial counts in the breast milk of women with mastitis. Lactobacillus salivarius PS2, taken at a dose of 1 billion colony-forming units (CFU) per day starting in late pregnancy, was tested in multiple trials for mastitis prevention. Research suggests this strain may work by lowering inflammatory markers in milk and boosting protective antibodies that help shield breast tissue from bacterial damage.
Who Should Be Cautious
The one group that warrants extra caution is immunocompromised mothers. The theoretical risk with probiotics is that the live organisms could, in rare cases, cause a systemic infection. Risk factors for this include immunosuppression, critical illness, and impairment of the intestinal lining. For healthy breastfeeding women, this risk is extremely low. But if you have a condition that significantly weakens your immune system, it’s worth discussing probiotic use with your care team before starting.
Choosing a Probiotic While Nursing
There are no strict dosage guidelines specifically for breastfeeding women. Most clinical trials have used doses in the range of 1 billion CFU per day per strain, which is a standard amount found in many over-the-counter supplements. The strains with the most safety data in lactating women are Lactobacillus and Bifidobacterium species. These are also the strains most commonly found in commercial supplements.
Probiotics are classified as dietary supplements, not medications, so they aren’t regulated with the same rigor as prescription drugs. Quality can vary between brands. Look for products that list specific strain names and CFU counts on the label, and choose brands that use third-party testing. A product that simply says “probiotic blend” without specifying strains or amounts gives you less to go on.