Conservatively, at least 100 million people are affected by house dust mite allergy worldwide, manifesting itself as asthma, rhinitis or atopic dermatitis. These minute arachnids, less than a third of a millimetre long, are present in almost every home, in our beds, clothing and carpets. The enzymes they produce in their guts in order to digest their food-fungi, bacteria and skin scales shed by humans are potent allergens, responsible for triggering asthma attacks and other allergic reactions. Despite the growing recognition of this major public health problem, and commitment of considerable research resources, there is still no simple, effective, generally applicable strategy for dust mite control.