Dust mites need dust and warm dark humid conditions to thrive, living in carpets, beds, bedding, curtains, upholstery and dusty areas (helped in no little way by our central heating and double glazing). The problem arises when the faeces become airborne and are inhaled, due to dusting, changing and making the bed etc. The main problem area is the bedroom and in particular the bed and bedding as we spend about 30% of our time there, and as we can perspire up to 1 litre in our sleep it provides the warmth and humidity required by the dust mites. It was widely thought that carpets caused a similar problem but recent research has found that carpets act like a filter, trapping dust and faeces (unlike hard surfaces where dust and faeces are easily made airborne with draughts and movement). In Sweden in the 70s carpets were blamed for asthma and due to the adverse publicity the use of carpeting decreased by 77% over 15 years up to 1990, over the same 15 year period the cases of asthma increased by 300%.

HOW TO TRY TO REDUCE ASTHMA ATTACKS.

Change pillows at least every 2 years (you can now buy anti allergy pillows)
Wash bedding as often as is practical
Vacuum your mattress regularly and have it cleaned every 2 years
Vacuum your carpets regularly and have them cleaned by means of hot water extraction as necessary
Don't use a feather duster, dust with a damp cloth rinsing it regularly
Ventilate rooms for at least 4 hours a day (especially after vacuuming)
Wash curtains yearly
As dust mites are sensitive to UV rays you could put your mattress in a sunny position for a couple of hours then vacuum out the dead dust mites.
Use a vacuum with a micro filter
Damp clean hard flooring so as not to lift dust and faeces