upper respiratory tract infections ( urtis ) are illnesses caused by an acute infection of the upper respiratory tract ( ie , the nose , sinuses , pharynx , or larynx ) . acute urtis include the common cold , acute sinusitis , acute pharyngitis , acute laryngotracheobronchitis ( croup ) , acute epiglottitis ( supraglottitis ) , acute rhino sinusitis and acute otitis media . acute urtis are a major cause of morbidity , especially in children and the elderly . common symptoms include cough , fever , headache , sore throat , runny nose , and sneezing . usually , the symptoms subside after a few days . to reduce fever and ease pain and headaches , paracetamol ( acetaminophen ) , ibuprofen , or aspirin how ever , misuse of antibiotics in acute urtis caused by viruses is common and may contribute to overuse of antibiotics and risk for development of antibiotic - resistant bacteria . probiotics are live microorganisms that might lead to health benefits when administered in adequate amounts . they are commonly consumed in fermented foods , such as yogurt and soy yogurt , or as dietary supplements . the underlying mechanisms of how probiotics may improve health are unclear , but improved local immunity ( by maintaining gut wall integrity ) and systemic immunity ( by enhancing nonspecific and specific arms of the immune system ) are possible explanations . this review was carried out to assess the effectiveness and safety of probiotics ( any specified strain or dose ) compared with placebo in the prevention of acute urti in people at risk of acute urti . not all research provides the same quality of evidence . the higher the quality , the more certain we are about what the research says about an effect . the words will ( high - quality evidence ) , probably ( moderate - quality evidence ) , and may ( low - quality evidence ) describe how certain we are about the effect ( table ) . summary of findings : probiotics compared to placebo for preventing acute upper respiratory tract infections patient or population : children and adults of all ages settings : day - care centers , hospital , or unclear intervention : probiotics the corresponding risk ( and its 95% confidence interval ) is based on the assumed risk in the comparison group ( ie , the median control group risk across studies ) and the relative effect of the intervention ( and its 95% ci ) . abbreviations : ci , confidence interval ; or , odds ratio ; rr , risk ratio ; urti , upper respiratory tract infection . grade working group grades of evidence high quality : further research is very unlikely to change our confidence in the estimate of effect . moderate quality : further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate . low quality : further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate . very low quality : we are very uncertain about the estimate . the included studies had heterogeneous populations ( ie , infants , children , marathon runners , and healthy volunteers ) . all participants in all 3 studies were children , which limits the generalizability of findings to adults . high statistical heterogeneity ( ie , i - square = 92% ) and high clinical heterogeneity ( ie , 1 of the 2 studies includes only marathon runners , and the other study includes the general population ) . the study with marathon runners is in favor of placebo ( although nonsignificant results ) ( md 1.60 ; 95% ci 0.34 to 3.54 ) and the study with the general population is in favor of probiotics ( md 1.90 ; 95% ci 2.04 to 1.76 ) . very wide confidence interval . unclear risk of bias in the smaller of the 2 studies ; however , the larger of the 2 studies had a low risk of bias the 10 studies that the cochrane authors reviewed showed that for people at risk of acute urti , compared with a placebo , probiotics may reduce the number of participants who experienced urti episodes ( at least 1 event ) , have an uncertain effect on the mean duration of an episode of urti because the quality of evidence is very low , may reduce the number of participants who used antibiotics , and may make little or no difference to adverse events . none of the studies measured the effect of probiotics on older people . in general , side effects are poorly documented and it is difficult to provide precise information . in these studies , the main side effects were gastrointestinal symptoms such as vomiting , flatulence , and increased irritability . however , pooled analysis showed no statistical difference between the probiotics group and the placebo group ( low - quality evidence ) . the cochrane collaboration is an independent global network of volunteers dedicated to summarizing research about healthcare . this information is taken from this cochrane review : hao q , lu z , dong br , huang cq , wu t. probiotics for preventing acute upper respiratory tract infections .