Causes

Allergies occur when your immune system reacts to a foreign substance such as pollen, pet dander or dust mites. Your immune system produces proteins known as antibodies that protect you from unwanted invaders that could make you sick or cause an infection.

When you have allergies, your immune system makes antibodies that identify your particular allergen as something harmful, even though it isn't. When you come into contact with the allergen, your immune system produces an inflammatory response in your nasal passages or lungs. Prolonged or regular exposure to the allergen can cause the ongoing (chronic) inflammation associated with asthma.

Dust mites eat organic matter such as skin cells people have shed, and rather than drinking water, they absorb water from humidity in the atmosphere.

Dust also contains the feces and decaying bodies of dust mites, and it's the proteins present in this dust mite "debris" that are the culprit in dust mite allergy.