Eczema is the most common inflammatory skin condition in children and contributes significantly to childhood morbidity.
The prevalence of allergic diseases among children, including eczema, has more than doubled during the past few decades and continues to rise.4 Furthermore, childhood eczema is associated with the development of other allergic diseases later in life, including asthma,5 a phenomenon referred to as the allergic march. The risk of developing asthma is nearly twice as high in people with childhood eczema compared to people with no history of eczema.5 As a result, there is considerable interest in identifying effective treatments for the primary prevention of childhood eczema in an effort to alter the progression of allergic disease. One proposed treatment option is probiotics, defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.6 Probiotics are generally regarded as safe, and so far no differences in gastrointestinal adverse event rates between probiotic and treatment groups have been reported.7 However, the safety and effectiveness of probiotics in childhood eczema remains under investigation, and the mechanisms by which they might exert positive effects on eczema are not completely understood.
Randomized Controlled Trials
Probiotics have been studied for both the primary prevention and treatment of childhood eczema. Primary prevention studies, the subject of this review, often employ a perinatal supplementation protocol in which pregnant women are supplemented during the final weeks of pregnancy, followed by direct supplementation of the infant. Such studies enroll mothers at high risk for delivering an infant likely to develop atopic dermatitis, with the risk factor determined by family history. In some prevention studies, at-risk infants are enrolled and supplemented within hours of birth.
To date, 10 distinct randomized controlled trials assessing different probiotics or probiotic combinations have been published on the primary prevention of eczema, and these trials have produced conflicting results. Among these studies, 7 have reported a decreased incidence of eczema in probiotic-supplemented infants, with a maximum risk reduction of 58% (the PandA trial). One study reported no decrease in the overall incidence of eczema, but a decrease in eczema in children with a positive IgE titer or skin prick test (SPT). Only one study has reported a decrease in the severity of eczema, as determined by the scoring of atopic disease (SCORAD) method.18 Three studies reported no change in the incidence of eczema, and one study reported an increased incidence in eczema in children with a positive SPT. Furthermore, 2 studies reported significant increases in sensitization or incidence of wheezing. This is in contrast to 2 reports of decreased sensitization in the breastfed infants of atopic mothers when the mothers were supplemented with probiotics. No preventive effects of probiotics on the development of other allergic diseases have yet been reported.