There are many studies regarding possible causes of increasing trend in frequency of allergic diseases in the last three decades. Main causes of this trend are: decrease of infectious diseases frequency, improvement in life level, changes in diet and lactic acid bacterias elimination from digestive tract. Less exposition to microbes can lead to the disturbance in optimal balance between Th1 and Th2 lymphocytes, prevalence of Th2 cytokines and excessively high production of IgE. Decreased exposure to microbes has resulted in the loss of main source of immune provocation, and a consequent increase in pathogenic immune responses and their associated diseases. Molecular interactions between immunocytes and microbes are mediated largely by Toll-like receptors (TLRs) on host cells and a diversity of ligands produced by viruses, bacteria and fungi.