What is that in household dust, that offends asthmatics?

Detailed Solution:

The correct answer is “Dust mites”.

Dust mites are microscopic organisms that thrive in household dust, particularly in warm and humid environments. Their feces and body fragments contain allergens that can trigger asthma and allergic reactions in susceptible individuals. Therefore, dust mites are a common allergen found in household dust that can exacerbate asthma symptoms.