Every year, we try to hold out against switching on the central heating but definitely, by the end of October, we will have succumbed and on it will go; there are only so many jumpers, socks and quilts you can pile on in the evenings! However, we are not the only ones who thrive once the central heating gets turned on.
House dust mites (or Dermatophagoides pteronyssinus or Dermatophagoides farinae) absolutely love central heating, together with other measures we have instituted into our housing to keep the heat in, such as fitted carpets. However, everyday things such as stuffed toys, mattresses and pillows are also, quite literally, stuffed with house dust mites too. In addition, the high humidities found in modern-day housing vastly contributes to high dust mite populations.
How do I get rid of house dust mites?
Remember, house dust mites are everywhere – not just your home but at school, work, the Tube, the train and the bus. They live off dead skin cells and so trying to completely eradicate them from your life is not realistic.
Measures to eradicate house dust mites include removal of fitted carpets, increased frequency of vacuuming, use of high filtration vacuums, installation of de-humidifiers, removal of stuffed toys, regular damp dusting, pesticide sprays and house-dust mite impermeable mattress and pillow covers. However, to employ all of these measures is not only costly but extremely time-consuming.
Is there any benefit to eradicating house dust mites?
Clinically, there is evidence that house dust mite eradication can reduce the severity of asthma.
[British Thoracic Society, National Asthma Campaign, The Royal College of Physicians of London in Association with the General Practitioner in Asthma Group, the British Association of Accident and Emergency Medicine, the British Paediatric Respiratory Society, the Royal College of Paediatrics and Child Health. The British Guidelines on asthma management: 1995 review and position statement. Thorax 1998; 52 (Suppl. 1): S1-21.]
However, the Cochrane reviews looking into the effectiveness of house dust mite eradication in asthma and a closely related condition, hayfever (or allergic rhinitis) have not been so conclusive.
[Gøtzsche PC, Johansen HK. House dust mite control measures for asthma. Cochrane Database of Systematic Reviews 2008, Issue 2. Art. No.: CD001187. DOI: 10.1002/14651858.CD001187.pub3.]
[Sheikh A, Hurwitz B, Nurmatov U, van Schayck CP. House dust mite avoidance measures for perennial allergic rhinitis. Cochrane Database of Systematic Reviews 2010, Issue 7. Art. No.: CD001563. DOI: 10.1002/14651858.CD001563.pub3.]
How can the studies not be conclusive?
If you look closely at the aforementioned Cochrane review looking at house dust mite avoidance measures for asthma, 54 trials were included, many of which were of poor quality. This was because many of the trials were small and of varying duration, did not adhere to good trial methodology and used a variety of eradication measures and hence were not comparable.
Also, the intervention group and the control group (no eradication measures) tended to improve. This is commonly seen in trials such as these because partaking in a trial looking at cleaning behaviour tends to make everyone start cleaning more!
It is also very difficult to ‘blind’ such trials. This is a feature of trials which prevents participants from altering their behaviour in response to partaking in the trial. This is particularly difficult in trials such as these as it is clearly obvious which group gets the mattress covers, special vacuum cleaner and pesticide spray when the other group clearly doesn’t.
So what advice does that leave us with?
Therefore, though the advice was that house dust mite control could not be recommended in the management of asthma, there were many criticisms that just because there was no evidence showing that house dust mite avoidance does work, it doesn’t necessarily mean that it doesn’t.
What about the study looking at hay fever?
The Cochrane review looking at house dust mite avoidance measures for hayfever, however, does state that all available trials were small and of poor quality and therefore affirming that it is difficult to offer any definitive recommendation on that basis.
How does this relate to eczema?
Now, asthma and allergic rhinitis are closely related to atopic eczema, and it has been suggested for many years that house dust mite reduction measures may be of benefit in the management of atopic eczema. This area has recently been reviewed in the British Journal of Dermatology.
[Garritsen FM, Ter Haar NM, Spuls PI. House dust mite reduction in the management of atopic dermatitis. A critically appraised topic. Br J Dermatol 2013; 168: 688-691.]
What has this review shown?
Not surprisingly, Garritsen et al concluded that there is not enough evidence to support house dust mite reduction in the management of atopic eczema. The authors looked at 1079 trials and shortlisted these down to 4 trials which were valid. Again, all 4 trials used a variety of eradication measures and were fairly small and one paper only followed patients for 6 months. This latter paper was the only one that showed any benefit and this could have been due to seasonal effects. In the other 3 trials, again both the intervention and non-intervention groups’ eczema scores improved, as in the asthma trials.
So where do we go from here?
The Cochrane Collaboration are performing a systematic review and this is currently being carried out, so we should wait to see what their advice is. Nevertheless, it may be that there is simply not enough large, high quality studies available using standardized methods of reducing house dust mite levels over a sufficient period of time and with standardized outcome measures, for any meaningful conclusions to be drawn.
Dr Sandy Flann, Consultant Dermatologist