Washing soft toys after putting them in the freezer overnight is a good way of reducing the asthma hazard to children posed by dust mites in the toys, University of Otago researchers say.

Recently published research by Associate Professor Rob Siebers, of the university's Wellington asthma, allergy and respiratory research group, and colleagues highlights the risks posed to children with asthma, arising from the mites in soft toys.

Researchers have known for some years that cold water washing removes allergens in the form of dust mite excreta but does not kill the mites.

The mites and their allergens are a serious issue for asthmatics and are strongly associated with the development of asthma in children, Professor Siebers says.

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"Children frequently sleep with their favourite toys close to their airways and this may be important for household dust mite-sensitised asthmatic children," he says.

"My advice for parents is to either tumble dry for one hour, or freeze the soft toy overnight, and then wash it in a cold wash to remove any allergens."

Dunedin resident Eileen Dawber today welcomed the research, which highlighted the importance of dust mite infestation in soft toys for some children with asthma.

The study findings also provided clear guidance on the most practical ways of reducing the mite-related allergen problems, she said.

Some parents may not have realised the importance of soft toys as a source of dust mites, if their young children had asthma and were sensitive to mite allergens.

"I think it's great they have highlighted it. It's an issue that a lot of people just haven't thought of before."

Many parents would also have not known the most cost-effective way of killing the mites and removing the allergens, she said.

She has asthma but her daughter, Pania Cullen, three, does not.

Dawber would nevertheless be following the Otago researchers' advice on countering dust mites, by freezing Pania's soft toys for 16 hours and then washing them in cold water.

Dawber would do this as a precautionary measure, so her daughter was not adversely affected by the allergens in future.

Her daughter often held her soft toy rabbit and other soft toys close to her face, illustrating the danger to airways the researchers had underscored, she said.

The study found infestations of house dust mites on soft toys could be eradicated by freezing, hot tumble drying or washing with eucalyptus oil and detergent.

All three of those methods were more effective than just washing toys, because the water needed to be above 55C to kill the mites, but that level of heat also damaged the toys, researchers said.

The study has just been published in an international journal, Paediatric Allergy and Immunology, and was conducted in association with colleagues at the Changhua Christian Hospital, Taiwan.

Freezing of toys for at least 16 hours at minus 15C resulted in a 95 per cent reduction of the mites, and hot tumble drying for one hour also reduced mites by 89 per cent.

The study's findings, have been forwarded to the Asthma Foundation.

- INDEPENDENT