'Asthma mites' infest one in four homes

Cockroach allergen could be found in bedding in more than 6% of homes.

Dust mites live primarily off flakes of skin, and deposit proteins from their guts which can cause allergy and asthma in humans.

The survey, carried out by the US Department of Housing and Urban Development, looked at levels of common allergens in a representative sample of 831 homes.

Researchers looked at vacuumed dust samples from the houses and compared this to health information from the families living there.

They found high levels of the dust mite proteins in bedding in 23% of the houses.

Certain types of household were more likely to have higher levels of dust mite allergen.

These included low income households, those with high bedroom humidity, older houses - built before 1978, and non-Hispanic ethnicity of inhabitants.

Dr Darryl Zeldin, the lead author on the study, presented to the American Thoracic Society conference in San Francisco, said: "This information can be used to identify homes and individuals that are at greatest risk of exposure so that researchers can better target their prevention and intervention efforts."

Frequent cleaning

He suggested that frequent and rigorous cleaning of bedding, the use of dehumidifiers and plastic barriers between mattress and sheeting could all help reduce the levels of allergen in homes.

The number of diagnosed asthmatics has been increasing rapidly in recent years - and dust mite allergen may well be a factor in either the development of the disease or in triggering attacks.

An expert on allergy and asthma, Dr Rob Niven, from the North West Lung Centre at Wythenshawe Hospital, Manchester, said: "In the UK most homes have sufficient house dust mite allergen in them to be relevant to the health of asthmatics.

"In the UK house dust mite is the most important allergen with 90% of childhood asthma being associated with allergy to house dust mite."

"There are of course parts of the world where there is very little house dust mite. Allergy and asthma are usually less common in these parts - and where present, is normally due to cockroach allergen, animals or pollen."

He said that it was important to target potential allergens to reduce the symptoms of asthma - and for sufferers to undergo skin tests to determine the source of their reaction.