The research undertaken by The Woolcock Institute of Medical Research suggests it’s elsewhere in the house, plus in offices and on public transport, where asthma sufferers really need to protect themselves.
The study, published this month in the scientific journal PLOS ONE documents how researchers, for the first time, measured dust mite exposure continuously throughout the day and night using an Australian-built prototype sampler. The clip-on device, the size of a small packet of cards, is the first ever to accurately measure the pattern of dust mite allergen exposure that people receive as they go through their day.
The researchers found on average only about 10% of the total daily exposure occurred while sleeping in bed at night. Another 50% occurred elsewhere in the house while 40% occurred outside the home, on transport and in offices and other buildings. There were wide variations between people.
“These figures debunk the 40 year old belief that the bed is the main site of allergen exposure,” said chief investigator Associate Professor Euan Tovey. “But, sadly, protecting yourself outside the bedroom poses all sorts of new challenges.”
House dust mites are the world’s most common allergy-causing protein, with up to 1.2 billion people displaying some allergy to mites. Exposure can cause symptoms such as sneezing, asthma symptoms, and red and watery eyes.
Research previously showed mites were common in bed dust, leading experts to believe beds were the site of the heaviest exposure. While it was also recognised that the mite allergens could be found in clothing, furnishings, carpets as well as in public buildings, scientists had not been able to determine to what extent these sites contributed to exposure.
The researchers enlisted 10 people who spent a total of 20 days continuously tracking their personal exposure using the novel device worn on their lapel. Particles were continuously collected around the edge of a small disk, the size of a 20 cent coin, which rotated once over a 12 or 24 hour period. Participants also wore a tiny camera which took photos every 15 seconds. The researchers measured exposure during separate activities by cutting the disk into an average of 20 tiny segments corresponding to the different activities observed in the pictures and then analysing each segment for allergen.
“We have long realised that most dust in houses and in clothing contains mite allergen,” says Associate Professor Tovey. “But what we had not sufficiently taken into account is that dust needs to be dispersed into the air by movement before it can be inhaled.
“Generally, you don’t move much in your sleep and so exposure in beds is much less than we thought. It was not until we actually measured airborne exposure though the day and night that the pattern of exposure became apparent,” he explains.
The researchers cautioned that the small study was indicative only, and additional studies of larger and different populations were warranted.
The finding makes the issue of reducing exposure more complicated. The results also help explain why most studies using specialist bed encasings alone have not been clinically effective. “It also means that whole-house approaches like air filtration, the better design of carpets and furnishings, and addressing other key exposure spots all needs to be re-examined in light of their contributions to exposure, ” said Associate Professor Tovey.
Asthma and House Dust Mites
- Asthma is one of the most common chronic disorders, affecting one in ten Australians
- Sufferers experience episodes of wheezing, breathlessness and chest tightness due to widespread narrowing of the airways
- The causes are still not well understood, but triggers are known to include viral infections, exercise, and exposure to allergens and irritants
- Mite allergens are the most common thing people are allergic to.
- These microscopic mites feast on flakes of human skin and are found in beds, furnishings and clothing. Much of the exposure to mites occurs via their faeces which carry the potent allergens. Studies suggest as many as 1.2 billion people worldwide could have some form of chronic sensitisation to dust mites
- Typical symptoms of house dust mite allergies include itchiness, sneezing, inflamed or infected eczema, red or watering eyes and a runny nose