**Part 2**

**Microorganisms in Atopic Dermatits** 

104 Atopic Dermatitis – Disease Etiology and Clinical Management

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**7** 

Itaru Dekio

*Japan* 

**Microorganisms and Atopic Dermatitis** 

*Department of Dermatology, Faculty of Medicine, Shimane University, Izumo* 

The relationship between microorganisms and human skin is complex. Some microorganisms are friendly residents, while others are harmful pathogens. Human skin has a variety of mechanisms for interacting with microorganisms, which promote the propagation of certain organisms while attacking others. Each of the different microorganisms discussed in this chapter has a unique relationship with humans. Their

To make the stories easier to understand, this chapter is divided into two sections. One section is devoted to the characteristics of the resident microbiota (microflora) of patients with atopic dermatitis (AD), while the other covers secondary infections that frequently occur in AD patients which are sometimes life-threatening. The microbiota of AD patients is significantly different from that of the normal population, and the relationship of microbiota

Human skin harbours many bacterial and fungal species, which are not apparently harmful. The total population of such residential microorganisms is known as the 'microbiota' (microflora). The microbiota is well balanced with the effect of natural human immunity, and the microorganisms have mechanisms to balance their population as a part of this community. Thus, it is appropriate to consider the microbiota as a 'microbial community'. It is generally accepted that the microbiota become stabilised at different points of balance in AD patients.

The microbiota of human skin differs largely according to skin sites. This is probably due to the fact that the structure and physiology of the surface of the skin differs at different sites of the body. This leads to the natural selection of certain species for particular sites. Thus, facial skin may be considered as a 'swamp' of sebum, soles could be considered as a 'pond' of sweat, axillae could be analogous to a 'rain forest', and forearms are 'deserts' which

As a reflection of this, for example, healthy facial skin harbours about 108 microbial cells per square centimetre, which comprises up to 2 g of microorganisms per face. On the other hand, healthy forearm skin harbours only 103 microbes per square centimetre. Therefore, in some body sites, the population is large enough to consider that the microbiota has a certain

This altered balance relates to the pathogenesis of AD as will be discussed below.

**1. Introduction** 

with AD is widely accepted.

**2.1 Ecology of skin microbiota** 

generally lack water and lipid.

stories are not simple but are quite interesting.

**2. The microbiota (microflora) and atopic dermatitis** 
