The skin condition atopic dermatitis (AD) is a highly prevalent condition, affecting 10%–20% of children in developed countries, with 60% of the cases starting during the first year of life.

AD is now recognized as mainly caused by abnormal epidermal barrier structure and function, and inflammation of the skin caused by abnormal immunological responses to antigens.

In addition, recent evidence suggests a link between altered gut microbiome and the development of AD.

Many studies support association between gut microbiota and AD. For example, it has been shown that the counts of bifidobacterium were significantly lower in patients with AD compared to counts in healthy individuals.

Researchers also show that differences in the gut microbial composition preceded the development of allergic diseases. They suggest that altered gut microbiota may be a cause of AD.

In any event, there is strong evidence that changes in the gut microbial composition caused by prenatal, perinatal, and postnatal influences play a role in the development of AD.

There were numerous studies on the use of probiotics in AD in the last decade. Lactobacillus and bifidobacterium are the 2 strains most widely used in these studies because early research showed reduced colonization of the gut by these 2 species in those with allergic diseases, compared to those without.

Prevention of AD

The use of probiotics has seen great benefits in the prevention of AD. Most studies have concentrated on the effect of the lactic acid producer, lactobacillus, alone or in combination with bifidobacterium.

A recent meta-analysis demonstrated that probiotic administration protects against the development of AD. It also concluded that lactobacilli alone or in combination with bifidobacteria are both protective.

Previous meta-analyses had concluded that probiotics significantly reduce the risk of developing AD, and there was an average decrease of 20% in the incidence of AD with probiotic use.

The consensus now is that administration of probiotics is beneficial in reducing the risk of developing AD.

The World Allergy Organization - McMaster University Guidelines for Allergic Disease Prevention (GLAD-P): Probiotics recommends the administration of probiotics to pregnant women with children at high risk for allergy, breastfeeding women with infants at high risk for allergy, and the infants themselves who are at high risk, with the main focus on the prevention of AD as the benefits of probiotics have shown the greatest effects in this regard.

The efficacy of probiotic use is influenced by many factors including dosage, strain, timing of administration, maternal flora, mode of birth delivery, antibiotic use, diet and nutrition, genetic and epigentic traits, basal gut microbial composition, and immune competency of the individual.

Protective effects seem most promising when administered both prenatally and and postnatally.

More studies are needed especially in terms of dosage, strain, mono or combination therapy (using single or multiple strains), and timing of therapy before probiotic use become standard prevention for AD.

Treatment with probiotic

In contrast to prevention, fewer studies have looked at administering probiotics as treatment for established AD in children. The results from these studies are mixed, with only some studies showing improvement. At present conclusions cannot be made with the current evidence.

A recent review suggests that synbiotics, the combined use of probiotic with specific prebiotics, may have greater potential than that already explored.

Although not many studies are available on synbiotics and AD, a meta-analysis found synbiotics to be beneficial in the treatment, but not in the prevention of AD.

This beneficial effect was particularly seen when using multiple probiotic strains and in children who were 1 year or older.

A study evaluating the benefits of synbiotics over prebiotics alone also found that Lactobacillus salivarius and FOS together helped improve moderate to severe childhood AD.

However, the number of published studies are small. More research is needed.