Besides your genetic predisposition, early exposure to house dust mite allergens may cause asthma.

A collective study of 67 children in Southampton, Poole and the University of Virginia showed that nearly half of the children had positive skin tests and raised antibody levels, indicating sensitivity to house dust mites. Their sensitivity was proportional to the level of mites recovered from their homes in house dust samples.The report did not examine early nutritional patterns, such as whether the children had been breastfed.

The report pointed to changes in houses, such as increased temperatures, fitted carpets, tighter insulation and certain detergents as all creating a breeding ground for the mites.

The results "suggest that high levels of exposure to inhaled allergens at an early age are important in the development of asthma," said the report. "When the present results are combined with those of previous studies showing an association of asthma with sensitization to house dust mite allergen, of the onset of asthma with exposure and of improvement of the disease with avoidance there seems to be sufficient evidence to suggest a causal relation between exposure to house dust mites and asthma. This implies that exposing young children to high levels of foreign proteins in their homes should be regarded as an important health risk."