Alongside allergies to tree and grass pollen, allergy to house dust mite is the most common respiratory allergy that I see amongst my patients. However, unlike pollen allergy which is seasonal and is only troublesome for a few months of the year, house dust mite allergy can be a significant issue all year round. The most classic story that I see in my clinic will be children who have a background of eczema who start to notice symptoms of stuffy nose, nasal itch, runny nose and itchy eyes which are particularly bad in the morning and then improve during the course of the day. The symptoms will be the same all year round although they tend to worsen in the autumn and winter when the windows are shut and central heating is on and improve during the spring and summer months when rooms are better ventilated. They might also notice a marked improvement when they go on far flung holidays. Most typically, every morning will be heralded by the child having a sneezing fit and this is a good indicator that dust mite will be to blame. The reason for this is that dust mites are at their happiest in warm moist environments such as soft furnishings, particularly beds, so most exposure happens overnight. Another common scenario will be sneezing fits or significant worsening of symptoms after bouncing up and down on a sofa, which will aerosolise all of the dust mite particles inside.
Although it is rather gruesome to think about it, it is not actually house dust mites themselves which are the cause of the allergy but their faecal particles. These contain digestive enzymes that are almost identical to those found in parasites that traditionally cause infestations in humans, but thankfully we tend not to see anymore in 21st century Britain. This close relationship between the proteins in these two enzymes is often used as an explanation for why we become allergic to house dust mite faeces, as the immune response involved in allergies is very similar to that involved in protecting us from parasitic infections.
There are three broad approaches to managing house dust mite allergy. The first is to try and minimise exposure and whilst this can be done to a meaningful level, it is rarely enough on its own to manage significant dust mite allergy. I always advise patients to focus particularly on the bed and the bedding as that is where most of the exposure happens and to think about getting house dust mite covers which are completely occlusive around the mattress as these are the most reliable, e.g. those from AllerGuard. Allergy UK has a Kitemark system that will help you differentiate dust mite covers that are effective from the many that aren’t, and it is worth looking at their site for their most up to date list. I generally advise against air purifiers, chemical treatments for soft furnishings and extreme measures such as pulling up all the carpets or taking down curtains as there is little evidence that they are helpful. The mites return very soon afterwards and as long as you have got a decent vacuum cleaner (ideally with a HEPA filter) and are using it once a week, then there should be no more dust mite allergen on the carpet than there is on a hardwood floor.
Another helpful measure can be to do a test to measure the amount of dust mite allergen in your home particularly in the child’s bedroom and I recommend a Ventia test from Indoor Biotechnologies (www.inbio.com) to do this. This can be helpful at making sure that the measures you have taken are working and should be done alongside measures to manage dust mite in soft toys which are often present in large numbers on children’s beds. These may need to have a visit to the freezer or the hot wash from time to time.
The second approach to managing house dust mite allergy is medication and this is usually a combination of simple measures such as saline nasal sprays and over the counter antihistamines but for more significant symptoms, then nasal sprays with anti-inflammatory steroids in can be very useful at calming symptoms down as are higher doses of non-sedating long-acting antihistamines. However, for those with more persistent and troublesome symptoms especially where they are contributing to asthma, then I tend to recommend consideration of immunotherapy – otherwise known as desensitisation. This is a treatment that involves exposing the immune system to a very large amount of dust mite allergen as a way of retraining it to be less reactive to it. Traditionally, this was done with injections but this can be a very arduous course especially for younger children whereas a similar effect can be obtained using sublingual immunotherapy where a tablet is placed under the tongue on a daily basis. This needs to be done for 6-12 months in order to get a significant effect so this is not a short-term treatment but if the course is continued for three years, then there is a long-term effect that goes beyond the course of treatment itself. We have been doing this for some years but it was very exciting to see in 2021 that ACARIZAX became the first fully UK licensed treatment for dust mite allergy having proven itself as clinically effective with a long-term effect. This is now something I am using more and more of as it is very well tolerated even in younger children and can make a real difference to the long-term management of house dust mite allergy.
