'There have already been a number of international studies that show synthetic bedding is associated with more asthma symptoms compared to feather bedding.'

Siebers' research looked at 178 samples obtained from 35 floors, 35 mattresses, 35 duvets and 73 pillows.

He says total beta glucan levels of synthetic pillows were two to three times higher than from feather pillows, although this just failed to reach statistical significance.

Mattresses older than five years also have about three times the amount of beta glucan compared to newer ones, said an Otago University release.

These findings were recently published in the Journal of Asthma.