and the capacity to help with intestinal balance. in the following decades, intestinal lactic-acid bacterial species with alleged health-beneficial properties were introduced as probiotics, including lactobacillus rhamnosus, lactobacillus casei, and lactobacillus johnsonii. etymology some literature gives the word a full greek etymology, but it appears to be a composite of the latin preposition pro, meaning 'for', and the greek adjective βιωτικός (biōtikos), meaning 'fit for life, lively', the latter deriving from the noun βίος (bios), meaning 'life'. the term contrasts etymologically with the term antibiotic, although it is not a complete antonym. the related term prebiotic comes from the latin prae, meaning 'before', and refers to a substance that is not digested, but rather may be fermented to promote the growth of beneficial intestinal microorganisms. research as food products or dietary supplements, probiotics are under preliminary research to evaluate if they provide any effect on health. in all cases proposed as health claims to the european food safety authority, the scientific evidence remains insufficient to prove a cause-and-effect relationship between consumption of probiotic products and any health benefit. there is no scientific basis for extrapolating an effect from a tested strain to an untested strain. improved health through gut flora modulation appears to be directly related to long-term dietary changes. claims that some lactobacilli may contribute to weight gain in some humans remain controversial. acute otitis media there is inconsistency in the results of different groups of 3488 children as reported in a cochrane review. also, it shows no significant difference regarding the adverse effects between probiotic and the other comparators. allergies only limited, low-quality evidence exists to indicate that probiotics are helpful for treating people with milk allergy. a 2015 review showed low-quality evidence that probiotics given directly to infants with eczema, or in infants whose mothers used probiotics during the last trimester of pregnancy and breastfeeding, had lower risk of eczema. asthma it is unclear whether probiotic supplementation helps with childhood asthma, as the quality of research evidence is low. antibiotic-associated diarrhea antibiotics are a common treatment for children, with 11% to 40% of antibiotic-treated children developing diarrhea. antibiotic-associated diarrhea (aad) results from an imbalance in the colonic microbiota caused by antibiotic therapy. these microbial community alterations result in changes in carbohydrate metabolism, with decreased short-chain fatty acid absorption and osmotic diarrhea as a result. a 2015 cochrane review concluded that a protective effect of some probiotics existed for aad in children. the known risks of using probiotics for treating clostridium difficile outweighs the uncertain benefits. probiotic treatment might reduce the incidence and severity of aad as indicated in several meta-analyses. for example, treatment with probiotic formulations including l. rhamnosus may reduce the risk of aad, improve stool consistency during antibiotic therapy, and enhance the immune response after vaccination. the potential efficacy of probiotics to treat aad depends on the probiotic strains and dosage. one review recommended for children l. rhamnosus or saccharomyces boulardii at 5 to 40 billion colony-forming units/day, given the modest number needed to treat and the likelihood that adverse events are very rare. the same review stated that probiotic use should be avoided in pediatric populations at risk for adverse events, such as severely debilitated or immune-compromised children. bacterial vaginosis probiotic treatment of bacterial vaginosis is the application or ingestion of bacterial species found in the healthy vagina to cure the infection of bacteria causing bacterial vaginosis. this treatment is based on the observation that 70% of healthy females have a group of bacteria in the genus lactobacillus that dominate the population of organisms in the vagina. specific strains of lactobacilli inhibit the growth of bacteria causing bv by producing h2o2, lactic acid, and/or bacteriocins, and/or inhibit the adherence of gardnerella vaginalis to the vaginal epithelium, which prevents the infection from occurring in the vagina. currently, the success of probiotic treatment has been mixed, since the use of probiotics to restore healthy populations of lactobacillus has not been standardized. often, standard antibiotic treatment is used at the same time that probiotics are being tested. in addition, some groups of women respond to treatment based upon ethnicity, age, number of sexual partners, pregnancy, and the pathogens causing bacterial vaginosis. in 2013, researchers found that administration of hydrogen peroxide-producing strains, such as l. acidophilus and l. rhamnosus, were able to normalize vaginal ph and rebalance the vaginal microbiota, preventing and alleviating bacterial vaginosis. blood pressure as of 2017, only limited evidence indicated any direct link between high blood pressure and gut microbiota. cholesterol a 2002 meta-analysis that included five double-blind trials examining the short-term (2–8 weeks) effects of a yogurt with probiotic strains on serum cholesterol levels found little effect of 8.5 mg/dl (0.22 mmol/l) (4% decrease) in total cholesterol concentration, and a decrease of 7.7 mg/dl (0.2 mmol/l) (5% decrease) in serum ldl concentration. depression and anxiety a 2019 meta-analysis found low-quality evidence for probiotics having a small improvement in depression and anxiety. a 2020 review found probiotics might improve depression, but more studies are needed. diarrhea some probiotics are suggested as a possible treatment for various forms of gastroenteritis. as a treatment for infectious diarrhea probiotics are of no benefit to people who have the condition for more than two days, and there is no evidence they lessen the duration of diarrhea overall. dermatitis probiotics are commonly given to breastfeeding mothers and their young children to prevent eczema (dermatitis), but no good evidence shows efficacy for this purpose. there is little evidence to support the use of probiotics to treat atopic dermatitis, and some risk of adverse effects. the american academy of dermatology stated: "the use of probiotics/prebiotics for the treatment of patients with established atopic dermatitis is not recommended due to inconsistent evidence". glycemic control according to an umbrella review of meta-analyses of randomized controlled trials, probiotics supplementation reduces glucose homeostasis. helicobacter pylori some strains of lactic acid bacteria (lab) may affect helicobacter pylori infections (which may cause peptic ulcers) in adults when used in combination with standard medical treatments, but no standard in medical practice or regulatory approval exists for such treatment. the only peer-reviewed treatments for h. pylori to date all include various antibiotic regimens. immune function and infections some strains of lab may affect pathogens by means of competitive inhibition (i.e., by competing for growth) and some evidence suggests they may improve immune function by increasing the number of iga-producing plasma cells and increasing or improving phagocytosis, as well as increasing the proportion of t lymphocytes and natural killer cells. lab products might aid in the treatment of acute diarrhea and possibly affect rotavirus infections in children and travelers' diarrhea in adults, but no products are approved for such indications. there are weak evidence probiotics might lower the incidence of acute upper respiratory tract infections in adults, they were better than placebo or no treatment. probiotics do not appear to change the risk of infection in older people. inflammatory bowel disease the use of oral probiotic supplements to modify the composition and behaviour of the microbiome has been considered as a possible therapy for both induction and maintenance of remission in people with crohn's disease and ulcerative colitis. a cochrane review in 2020 did not find clear evidence of improved remission likelihood, nor lower adverse events, in people with crohn's disease, following probiotic treatment. for ulcerative colitis, there is low-certainty evidence that probiotic supplements may increase the probability of clinical remission. people receiving probiotics were 73% more likely to experience disease remission and over 2x as likely to report improvement in symptoms compared to those receiving a placebo, with no clear difference in minor or serious adverse effects. although there was no clear evidence of greater remission when probiotic supplements were compared with 5‐aminosalicylic acid treatment as a monotherapy, the likelihood of remission was 22% higher if probiotics were used in combination with 5-aminosalicylic acid therapy. whereas in people who are already in remission, it is unclear whether probiotics help to prevent future relapse, either as a monotherapy or combination therapy. irritable bowel syndrome probiotics are under study for their potential to affect irritable bowel syndrome, although uncertainty remains around which type of probiotic works best, and around the size of possible effect. necrotizing enterocolitis several clinical studies provide evidence for the potential of probiotics to lower the risk of necrotizing enterocolitis and mortality in premature infants. one meta-analysis indicated that probiotics reduce these risks by more than 50% compared with controls but that further, large, high-quality trials were needed to inform policy and practice. pregnancy a cochrane systematic review found no good evidence that probiotics were of benefit in reducing the risk of gestational diabetes, but good evidence that they increased the risk of pre-eclampsia. for this reason, the use of probiotics in pregnancy was advised against. recurrent abdominal pain a 2017 review based on moderate to low-quality evidence suggests that probiotics may be helpful in relieving pain in the short term in children with recurrent abdominal pain, but the proper strain and dosage are not known. urinary tract there is limited evidence indicating probiotics are of benefit in the management of infection or inflammation of the urinary tract. one literature review found lactobacillus probiotic supplements appeared to increase vaginal lactobacilli levels, thus reducing the incidence of vaginal infections in otherwise healthy adult women. general research formulations supplements such as tablets, capsules, powders, and sachets containing bacteria have been studied. however, probiotics taken orally can be destroyed by the acidic conditions of the stomach. as of 2010, a number of microencapsulation techniques were being developed to address this problem. multiple probiotics preliminary research is evaluating the potential physiological effects of multiple probiotic strains, as opposed to a single strain. as the human gut may contain several hundred microbial species, one theory indicates that this diverse environment may benefit from consuming multiple probiotic strains, an effect that remains scientifically unconfirmed. strains only preliminary evidence exists for most probiotic health claims. even for the most studied probiotic strains, few have been sufficiently developed in basic and clinical research to warrant approval for health claim status by a regulatory agency such as the fda or efsa, and as of 2010, no claims had been approved by those two agencies. some experts are skeptical about the efficacy of different probiotic strains and believe that not all subjects benefit from probiotics. scientific guidelines for testing first, probiotics must be alive when administered. one of the concerns throughout the scientific literature resides in the viability and reproducibility on a large scale of observed results for specific studies, as well as the viability and stability during use and storage, and finally the ability to survive in stomach acids and then in the intestinal ecosystem. second, probiotics must have undergone controlled evaluation to document health benefits in the target host. only products that contain live organisms shown in reproducible human studies to confer a health benefit may claim to be probiotic. the correct definition of health benefit, backed with solid scientific evidence, is a strong element for the proper identification and assessment of the effect of a probiotic. this aspect is a challenge for scientific and industrial investigations because several difficulties arise, such as variability in the site for probiotic use (oral, vaginal, intestinal) and mode of application. third, the probiotic candidate must be a taxonomically defined microbe or combination of microbes (genus, species, and strain level). it is commonly admitted that most effects of probiotics are strain-specific and cannot be extended to other probiotics of the same genus or species. this calls for precise identification of the strain, i.e. genotypic and phenotypic characterization of the tested microorganism. fourth, probiotics must be safe for their intended use. the 2002 fao/who guidelines recommend that, though bacteria may be generally recognized as safe (gras), the safety of the potential probiotic be assessed by the minimum required tests: assessment of certain metabolic activities (e.g. d-lactate production, bile salt deconjugation) assessment of side effects in human studies determination of antibiotic resistance patterns epidemiological surveillance of adverse incidents in consumers (aftermarket) if the strain under evaluation belongs to a species known to produce toxins in mammals, it must be tested for toxin production. one possible scheme for testing toxin production has been recommended by the eu scientific committee on animal nutrition. if the strain under evaluation belongs to a species