Probiotics, Prebiotics and Postbiotics in Atopic Dermatitis

‘Atopic dermatitis (AD) is one of the most common chronic inflammatory disease of the skin. It affects about 15%-30% of children and 5-10% of adults. Although it most often starts in infancy, it may also develop during adolescence or adult life [1]. AD is characterized by dry skin, pruritus and eczematous skin lesions, that typically show age-related morphology and distribution [1,2]. Clinicians rely on clinical measures to assess the severity of disease and the outcomes of therapy. The most commonly used assessment tools include the SCORing Atopic Dermatitis (SCORAD) and Eczema Area and Severity Index (EASI) that have been validated to be used in both clinical settings and clinical trials [3]. AD has a profound impact on the quality of life of the patients and their families because of the burden of its complex signs and symptoms (itch, pain, sleep disturbance...) that affect social functioning and psychological well-being [4-6]. For these reasons, patients-reported symptoms and quality of life are also increasingly important in clinical practice [7,8].


Introduction
' Atopic dermatitis (AD) is one of the most common chronic inflammatory disease of the skin. It affects about 15%-30% of children and 5-10% of adults. Although it most often starts in infancy, it may also develop during adolescence or adult life [1]. AD is characterized by dry skin, pruritus and eczematous skin lesions, that typically show age-related morphology and distribution [1,2]. Clinicians rely on clinical measures to assess the severity of disease and the outcomes of therapy. The most commonly used assessment tools include the SCORing Atopic Dermatitis (SCORAD) and Eczema Area and Severity Index (EASI) that have been validated to be used in both clinical settings and clinical trials [3]. AD has a profound impact on the quality of life of the patients and their families because of the burden of its complex signs and symptoms (itch, pain, sleep disturbance...) that affect social functioning and psychological well-being [4][5][6]. For these reasons, patients-reported symptoms and quality of life are also increasingly important in clinical practice [7,8].
Actually, common therapeutic strategies for AD include hydration with emollients, avoidance of individual trigger factors, anti-inflammatory therapy with topical corticosteroids or calcineurin inhibitor and treatment of secondary infections [9][10][11]. Increasing evidence shows that patients affected by AD have a modified composition of the gut microbiome and lack microbial diversity compared to healthy controls [12,13]. This bacterial dysbiosis may be considered a possible target for the treatment and prevention of AD. Therefore, the supplementation of the diet with probiotics, prebiotics and postbiotics may have a role in the management of AD because of their capacity of modulation of the microbiota.
The accepted definitions of probiotics, prebiotics and postbiotics are: A. Probiotics: probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host [14]; B. Prebiotics: a prebiotic is a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host wellbeing and health [15];

C.
Postbiotics: postbiotics are bioactive compounds produced by food-grade microorganisms during a fermentation process. Postbiotics include microbial cells, cell constituents and metabolites [16]. In this short review we summarize the currently available evidence on the role of probiotics, prebiotics and postbiotics in the prevention and treatment of AD.

Probiotics in AD
Probiotics are the most studied -biotic products for the prevention and treatment of AD. Most of the studies that evaluate the effectiveness of probiotics in the prevention of AD involve the intake of probiotics by the mother during pregnancy and the subsequent effect on infants and children. Concerning the prevention of AD, the meta-analysis by Doege et al. [17], which included seven

Prebiotics in AD
The effect of prebiotics supplementation on the prevention and treatment of AD has been less studied than the effect of probiotics supplementation. One meta-analysis evaluated the effect of prebiotics supplementation on the prevention of allergy.  to −0.07, p value=0.048). The evidence for the use of synbiotics for the prevention of AD is not strong [25].

Postbiotics in AD
The

Conclusion
The supplementation of the diet with probiotics seems to have a beneficial role in AD, especially regarding its prevention. Strong evidence is still lacking to recommend the use of probiotics in the treatment of AD, mostly due to the high heterogeneity of studies and strains used. In general, -biotic products seem to have a beneficial effect on AD. However, the evidence in favor of supplementing the diet with -biotics for the management of AD is still not enough to make clear recommendations.