**1.1 What are probiotics?**

The year 2011 marks the 104nd year since Eli Metchnikoff suggested that the consumption of lactic acid bacteria may benefit the human host's immune system [11]. However, not until the mid–1960 did the term probiotic become the trend. Probiotics means "for life" and is defined by the World Health Organization and the Food and Agriculture Organization of the United Nations as "live microorganisms which, when administered in adequate amounts as part of food, confer a beneficial health effect by producing gut microflora on the host." These probiotics are mainly represented by lactic acid bacteria [12]. Simply; probiotics are ingested live microbes that can modify intestinal microbial populations in a way that benefits the host.

#### **Characteristics of probiotics**

There are several generally accepted characteristics that define probiotic bacteria. Probiotics:

are microbial organisms;


### **1.2 Atopic dermatitis (eczema)**

354 Atopic Dermatitis – Disease Etiology and Clinical Management

fed infants. Formula-fed infants, on the other hand, tend to have a flora that is more complex, consisting mostly of Coliforms and Bacteroides, with significantly lower the prevalence of Bifidobacteria [7]. After weaning, the microflora of children begins to resemble that of adults, with increased Bacteroides, Veillonella, and Fusobacterium [8]. Epidemiologic data showed that atopic children have a different intestinal flora from that of healthy ones, with higher levels of Clostridia and lower levels of Bifidobacteria. Furthermore, other studies have also shown that early colonization with potentially more pathogenic bacteria such as Clostridium difficile and Staph. aureus is more likely to occur in children who go on to develop allergy. In contrast, lactic acid bacteria and Bifidobacteria are found more commonly in the composition of the intestinal flora of non-allergic children. The enhanced presence of these probiotic bacteria in the intestinal microbiota seems to correlate with protection against atopy [9,10]. Based on these data, "harmless" microbial agents that are probiotics have been presently tested for their efficacy in the prevention and therapy of

The interest in probiotic therapeutic potential in allergic disorders stemmed from the fact that they have been shown to improve intestinal permeability and reduce inflammatory cytokines. Such effects would be desirable in treating allergic disorders including atopic dermatitis (AD). Therefore, several studies have been designed to examine the efficacy of probiotics in many allergic conditions, such as eczema and food allergies [13,14]. Including the first publication in 1997, over 30 randomized, double-blind, placebo-controlled clinical trials have been conducted to study the effects of various probiotics on treatment and prevention of allergic diseases. In total, almost 3000 individuals (including those in placebo groups) have participated in these studies so far. In the first-time study done by Majamaa and Isolauri in 1997, the administration of LGG to highly selected patients (age <2 years, challenge-proven cow's milk allergy, and mild-to- moderate eczema) significantly improved the total SCORAD score [15]. Later the Finnish study of Kalliomaki was the first report to describe that the frequency of AD in neonates treated with Lctbs rhamnosus GG (LGG) was half that of the placebo [16]. However, these results recently have been questioned by other trials, which reported no difference in the development and therapy of AD in neonates supplemented with LGG or other probiotics. Therefore, an allergen-preventive or therapeutic effect of probiotics in AD could not be consistently established. The aims of this chapter are to comprehensively define probiotic properties and to characterize current knowledge of probiotics, including the key mechanisms

of probiotic effects as well as their preventative/ therapeutic role in AD at last.

The year 2011 marks the 104nd year since Eli Metchnikoff suggested that the consumption of lactic acid bacteria may benefit the human host's immune system [11]. However, not until the mid–1960 did the term probiotic become the trend. Probiotics means "for life" and is defined by the World Health Organization and the Food and Agriculture Organization of the United Nations as "live microorganisms which, when administered in adequate amounts as part of food, confer a beneficial health effect by producing gut microflora on the host." These probiotics are mainly represented by lactic acid bacteria [12]. Simply; probiotics are ingested live microbes that can modify intestinal microbial populations in a way that benefits the host.

There are several generally accepted characteristics that define probiotic bacteria. Probiotics:

allergy in infants [11-14].

**1.1 What are probiotics?** 

**Characteristics of probiotics** 

are microbial organisms;

Atopic dermatitis (AD) is the most common chronic skin condition in infants and children, with a prevalence of 10- 20% in population. Geographic location affects the prevalence of this disease, with the highest prevalence in the United States and Europe [17]. Important factors in the susceptibility to develop AD include a genetic basis and environmental factors. Eczema refers to a chronic or relapsing itchy skin inflammation with typical lesions and locations. AD has been linked to food hypersensitivity, especially milk and egg proteins. However, 40-60% of children with AD may not develop IgE sensitization [18]. The term eczema has been recently proposed, but for practical purposes, both AD and eczema will be used in this chapter.

There have been several proposed methods for classifying the severity of AD in various research studies mentioned in this chapter, but only the Scoring of AD Severity Index (SCORAD), established by the European Task Force on AD, has been validated for reproducibility and accuracy in assessing therapeutic response [17,18]. The SCORAD combines objective measures, such as extent and severity of skin lesions, and subjective criteria, such as pruritus and sleep loss. Children with AD can be further classified as having mild: (≤25), moderate: (25-50), or severe: (≥50) disease based on their SCORAD score.
