In 1967, a mite in dust (Dermatophagoides pteronyssinus) was shown to cause a skin reaction; it has since been considered as the main house dust allergenic agent in the Netherlands, and subsequently in other countries such as the United Kingdom, Australia, Japan and Brazil.7 House dust allergens were purified during the following decades; the cat (Felis domesticus) allergen - Fel d 1 - was the fir