Background: House Dust Mites (HDMs) are various species of acariform mites found in association with dust in residences. They are tiny creatures, about a quarter of a millimeter long, that are documented to cause allergies. They Feed on dead human skin cells and prefer warm and humid conditions. Up to date, 39 allergens of the HDM genus Dermatophagoides have been documented by the Allergen Nomenclature Subcommittee of the World Health Organization (WHO) and the International Union of Immunological Societies (IUIS). They are named (Der p) or (Der f) after mite species (Dermatophagoides pteronyssinus or Dermatophagoides farinae), respectively and are numbered according to their chronological identification or homology to previously discovered allergens in other mite species. Recognizing the correlation between allergen sensitization and disease provides valuable information for the clinicians in prevention and treatment of allergic diseases related to HDM. HDM allergens are considered among the most prevalent perennial allergens that are difficult to eliminate. They are found to induce allergic inflammation in respiratory mucosa, cause nasal obstruction, and disturb sleep. The German Multicenter Allergy Study observed participants sensitized to HDM from birth until the age of 20 years and reported that early mite allergen sensitization during childhood was associated with polysensitization to mite and a higher risk to develop allergic rhinitis or asthma. In this review article we will give brief microbiological overview about House Dust Mites and Allergy.