NOSE plugs that filter out fine particles such as pollen and dust could provide an alternative to drugs for the 10 per cent of people who suffer from severe hay fever. An initial trial of the filters suggests they may even be more effective than existing medications.
There have been numerous attempts to create such nasal filters, with at least 90 patents filed since 1902. But almost all of them work on the 鈥渢ea-strainer鈥� principle, which impedes breathing, especially as the filter gets clogged.
Now a team at the Woolcock Institute of Medical Research in Sydney claims it has successfully tested a filter that traps pollen on a sticky surface. This kind of filter doesn鈥檛 get bunged up, though you do have to replace the sticky part regularly.
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In the trial, 47 hay fever sufferers spent two hours in parkland on two different days, 24 of them wearing a dummy device, and the rest using a genuine filter. Skin-prick tests showed that each volunteer was sensitive to the pollens present at the test site. But while those who wore a dummy device suffered hay fever as usual, the others had far fewer symptoms.
鈥淲e were surprised at how big the effect was,鈥� says team member Tim O鈥橫eara. 鈥淪imilar studies with antihistamines tend to get much smaller differences.鈥� The results, reported at a recent meeting of the Australasian Society for Clinical Immunology and Allergy in Adelaide, have yet to be published
O鈥橫eara won鈥檛 say what the sticky material in the filter is made from, as this part of the device is not protected by the team鈥檚 US patent. But he says it was tricky to develop. 鈥淎t the microscopic level, pollen grains are like rubber balls,鈥� says O鈥橫eara. 鈥淭hey have a tendency to bounce off surfaces.鈥�
To trap as many particles as possible, the filter forces the air to make a right-angle turn, so that the pollen grains hit the sticky surface head-on (see Graphic). Folds of flesh called turbinates do a similar job in the nose. But the filter catches the grains before they enter the nasal cavity, removing 97 per cent of ryegrass and ragweed pollens, two main triggers for hay fever worldwide.
The researchers envisage people using their filters when they go outside or on days when the pollen count is likely to be high. The filters would be particularly useful for people who can鈥檛 tolerate nasal steroids, or who suffer side effects from antihistamines. 鈥淲e haven鈥檛 had people using the filters every day all through the spring, but they are pretty easy to breath through and no one complained about them being uncomfortable in the clinical trial,鈥� O鈥橫eara says.
The filter devices might also help relieve other allergies, such as asthma. Tests suggest they can filter out up to 80 per cent of allergens in household dust and roughly 65 per cent of allergens from cats. But the team is still working on improvements, and it will be at least two years before the filters go on sale.