HDM allergy is highly prevalent and can manifest in the respiratory system as allergic rhinitis, allergic asthma, or both but should be thought of as one common condition affecting the whole respiratory tract. Although mite populations are constrained by humidity, the adaptive spread of the HDM, overlapping as it does with human habitation, suggests that it thrives in preferred human living conditions. Therefore controlling exposure is challenging. Studies indicate that HDM allergen levels should be maintained at less than 2 μg/g to decrease the likelihood of sensitization; however, measures to decrease HDM exposure have shown little or no benefit on symptoms in sensitized subjects.