Probiotics are living microorganisms that are intended to benefit the body. While some microorganisms have a bad rap, like “germs” for example, many types are helpful.
Some help digest food, destroy disease-causing cells, and produce vitamins. There are many different types of beneficial microorganisms. This large network of microorganisms is collectively called your “microbiome”.
Microorganisms can even be found in amniotic fluid and the gut of an infant before they are born and continue to exist in the human gut for a lifetime.
Your microbiome changes and this can be good or bad.
When the microbiome becomes disturbed in a negative way sometimes additional probiotic products may help your body return to a better state of health by balancing out the community of microorganisms that lives in your gut.
Treatment for health conditions using probiotics is still being researched. It’s hard to say which probiotics are helpful, how much to take, and who would benefit from specific types.
Many of the microorganisms in probiotic products are the same as or similar to microorganisms that naturally live in our bodies. That is the point!
The seven microbial organisms most often used in probiotic products are:
Each of these have different health effects and different strains within each of these can also vary in their effects on the body.
Here are Dr. Trill’s favorite articles on probiotics:
What do probiotics have to do with breastfeeding parents with food allergy babies?
Human milk provides many of these good microorganisms to the infant's gut. They help with digestive and immune function in the developing baby. [1, 2] According to one study, the most commonly isolated species of probiotics in breastmilk belong to the genera Staphylococcus, Streptococcus, Lactobacillus, and Bifidobacterium. 
More sensitive studies have recovered an even higher diversity of microorganisms in breast milk including Enterococcus and Lactococcus, Veillonella, Gemella, Cutibacterium and Staphylococcus, Pseudomonas, and Sphingomonas, but these results differ significantly between individuals. [4, 5] These microorganisms in breastmilk seem to come from the maternal gut, breast tissue, and infant oral cavity. 
So, the gut microbiome can be one factor that contributes to shaping the microorganisms in our milk. These milk microorganisms then influence the baby’s microbiome and in turn, can impact allergy and immune responses.
There are several conditions in infants that are likely affected by probiotic microorganisms.
Some studies have shown differences in the types of microbes of babies who do have colic and those who don’t. A 2018 review of several studies involving the use of the probiotic Lactobacullus reuteri DSM 17938 to treat colic was successful in exclusively breastfed infants and no harmful effects were seen from giving babies this microbe. 
This condition can occur in premature infants and can have fatal consequences. A reaction to food components and the microorganisms that live in a premature baby’s digestive tract may contribute but the exact cause is still unclear. A 2017 review of several studies showed that probiotics helped to prevent necrotizing enterocolitis in very low-birth-weight infants. The results of each of the individual studies varied. Probiotics that included both Lactobacillus and Bifidobacterium seemed to produce the best results, but it was not possible to identify the most beneficial strains within these large groups of microorganisms. 
While no short-term side effects were seen, long-term effects of probiotics at a very young age are still uncertain. There have also been instances where babies developed bloodstream infections from the same microbes intended to be used for probiotic purposes. 
A serious illness in which the body has a harmful response to an infection causing major organs to stop working and can be life-threatening. The risk of sepsis is higher in infants. One group, particularly at risk for sepsis, is premature infants. A review of 37 studies (9,416 participants) found that probiotics helped reduce the risk of sepsis in premature infants. 
New research is suggesting a link between milk microorganisms, pediatric asthma, and allergy by way of modulation of gut microorganisms. However, commercial probiotics for asthma prevention are still inconclusive. 
Some studies and meta-analyses show that exposure to probiotics during pregnancy and in early infancy might reduce the risk of developing eczema in children. A 2018 meta-analysis included 27 randomized controlled trials (RCTs) and one controlled cohort study in a total of 6,907 infants and children exposed to probiotics in utero for 2 weeks to 7 months (via maternal oral supplementation) and/or by oral administration to the infants after birth for 2 to 13 months. Between ages 6 months and 9 years, probiotic treatment with single strains or mixtures that included Lactobacillus, Bifidobacterium, and Propionibacterium strains significantly reduced the risk of atopic dermatitis (ecze