Asthmatics should not waste money on special mattress protectors and vacuum cleaners to tackle dust mites - as they are of little use, experts have said.
Many asthmatics are allergic to tiny mites that live in dust in carpets, bedding and cuddly toys.
The Cochrane Collaboration research group reviewed 54 earlier studies, involving 3,002 people, to assess how well specialist equipment worked.
They found there was some dust mite reduction but nothing too significant.
Mattress protectors, specialist cleaners, high-efficiency vacuum cleaners and air filters were among the products tested..
Thirty-six trials assessed physical methods, such as mattress casings, 10 chemical methods, and eight a combination of chemical and physical methods.
The products were largely ineffective, but the team did find mite reduction occurred in 17 trials although it was judged not significant enough to help ward off asthma.
The level of allergens is so high in most homes that what remains after the treatment is still high enough to cause asthma attacks
Dr Peter Gotzsche, lead author
Lead author Dr Peter Gotzsche said: "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.
"If you are wondering why it is that mattress covers and the other strategies are not effective, the likely answer is that all these treatments do not have a large enough effect on the occurrence of allergens from house dust mites.
Allergy UK's Jules Payne advises using asthma equipment
"The level of allergens is so high in most homes that what remains after the treatment is still high enough to cause asthma attacks."
Leanne Male, assistant research director at Asthma UK, said: "This updated review confirms previous evidence which suggests that dust prevention methods have little effect on reducing overall asthma symptoms."
She said the charity recommended washing bed linen at high temperature and removing soft toys from beds could make life easier for the 90% of people whose asthma is triggered by dust mites and may enable them to manage their asthma with less medicine.
There are currently 5.2m people in the UK receiving treatment for asthma.
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