The biggest single cause of an asthma attack is the faeces of house dust mites. But there are several things you can do that may help.
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Whether they are relevant to you will depend on the causes of your allergy and the severity of the attacks.
Buy allergen-barrier bedding covers which can be damp dusted. These are available from some local asthma societies or Air-Flow Products.
Have a carpet-free bedroom - or even a carpet-free home - and regularly wet-mop the floors.
Damp dust every week. Alternatively, use your vacuum cleaner's dusting brush. Avoid feather dusters, which create a cloud of dust.
Choose a vacuum cleaner with a sealable and disposable dustbag.
Vacuum carpets and soft furnishings at least once a week with a cleaner that has a good filtration system such as HEPA, S-class or replaceable micro-filters (see below for more information). The vacuuming probably won't remove the live mites, as they are very good at clinging to soft surfaces, but it does remove the faeces.
If possible, get someone else to vacuum. If not, open the windows and wear a mask, then leave the room and let the air settle for 20 to 30 minutes.
Ensure the cleaner's dust compartment is emptied regularly (by someone else).
Steam-cleaning carpets and upholstery may reduce the levels of dust mites for a short period, but the residual water left from the cleaning may promote fungal growth, which can also trigger asthma.
If you or someone in your household is asthmatic, your doctor can organise an allergy test.
Most vacuum cleaners suck up the dust and dirt along with a whole lot of air. They then filter that air through a dustbag and some other kind of filter, and blow the filtered air out a vent.
But this doesn't necessarily mean they will trap the fine particles, cat allergens and dust mites that can trigger an asthma attack.
For many asthma sufferers and others with an allergy to dust mites, this can be an awful problem.
The best solution is a HEPA filter, which is designed to block small particles of dust. European manufacturers sometimes use the term S-class instead.
HEPA conforms to a worldwide standard for filters required to trap 99.97 percent of particle emissions down to 0.3 microns in size. One micron is one thousandth of a millimetre: enough to screen cigarette smoke and even bacteria.
Note that HEPA filters lose their efficiency as they clog with dust, so they need to be replaced or washed about once a year.