Atopic dermatitis (AD) is a complex disease that is influenced by genetic and environmental factors. An increasing body of evidence suggests that the body´s colonizing microbiota are important in the pathophysiology of AD. Standard culture as well as molecular techniques allowing identification of microorganisms, that are not culturable, have demonstrated that the skin microbiota in patients with AD diffes from those in controls.
Antimicrobial peptides play an essential role in protecting the skin by direct killing of pathogens. Observations that β-defensins were deficient in patients with AD suggest decreased antimicrobial peptide expression as a possible cause of the altered skin microbiota.
The skin´s first line of defense against invasion by microbial agents is the stratum corneum, a nonviable, desiccated layer of the epidermis. This physical barrier is however susceptible to injuries that allow the entry of opportunistic microbial agents into the skin. The innate immune system can immediately respond to this intrusion by helping to prevent further invasion.