All about mite droppings
House dust mite droppings consist of 3 to 5 food balls bound together by mucus. The ball is then wrapped tightly in a semipermeable membrane and egested. Egestion is the proper term for excretion of undigested food contained in feces.
Once out of the mite’s body the dropping will be held together until it is either eaten by the mite, dissolved upon contact with moisture or broken up by disturbance. The average intact mite dropping is 10 to 40 microns in size. However, in one research paper scientists observed airborne particles containing mite allergens that ranged from 5 to 40 microns. These were described as either feces, fibres or flakes of translucent particles.
Particle size matters for people who are sensitive to house dust mites because the smaller the fecal particle carrying active enzymes, the deeper it can travel into the lungs, even reaching delicate areas of gas exchange. To date scientists have identified 7 different active enzymes from mites. In general, inhaled particles above 10 microns will land on the trachea or bronchi while smaller dust (below 10 microns) has the potential to reach and be deposited in the alveoli. The alveoli is the last stop in the branches of our lungs and where gases are exchanged.References
'Mite allergen (Der p1) is not only carried on mite feces', Sandra De Lucca, Richard Sporik, Timothy J. O;Meara, Euan R. Tovey, J Allergy Clin, Immunol. 1999, 103: 174-5
'Nitric oxide production by alveolar macrophanes in response to house dust mtie fecal pettets and the mite allergens, Der p1 and Der p2', Peak HL, Currie AJ, Stewart GA, Mc William AS, 2003, J. Allergy Clin. Immunol. Vol. 112, Number 3, p 531-537
'Mechanisms of particulate matter toxicity', S. Salvi, ST Holgate, 1999, Clin. Exp. Allergy, Vol. 29, p 1187-1194
Mite Allergens, Enrique Fernandez-Caldas, Leonardo Puerta, Luis Caraballo, Richard F Lockey, Clin. Allergy Immunol. 2008; 21: p 161-182