Asthma sufferers should stop wasting money on special devices to tackle dust mites, experts have said.
A study found mattress protectors and vacuum cleaners failed to effectively curb the allergens that can trigger asthma attacks.
Some asthmatics are allergic to the tiny mites that live in dust around the house, such as in carpets, bedding, soft furnishings and cuddly toys.
House dust also contains a large number of different allergens.
Methods aimed at tackling the mites include mattress and pillow protectors, washing bedding at higher than 60 degrees, anti-house dust mite cleaning products, high efficiency vacuums and air filters.
But a new review published by The Cochrane Collaboration has found no evidence that such methods are effective.
Lead author Dr Peter Gotzsche, director of The Nordic Cochrane Centre in Copenhagen, Denmark, said some of the studies showed a more than 50% reduction in allergens but even 90% is insufficient.
"We can conclude with confidence that there is no need to buy expensive vacuum cleaners or mattress covers or to use chemical methods against house dust mites, because these treatments do not work," he added.
There are currently 5.2 million people in the UK receiving treatment for asthma.
Will you be recommending that people with asthma save their money for evidence-based treatments? Your comments: (Terms and conditions apply)
"From personal experience, I bought new pillows and antidustmite pillow cases, very cheaply from the internet. My nocturnal asthma symptoms improved considerably and I was able to decrease my inhaled steroid. I will still continue to tell my patients that from personal experience, I found antidust mite pillow cases effective. They can then make up their own mind whether to try or not, however, I would not buy an expensive vacumn cleaner." - Teresa