What are house dust mites and how do I know if I’m allergic to them?

People often believe they are allergic to house dust. But of the 20% of Australians suffereing with allergies, a number are are actually allergic to microscopic house dust mites.

House dust mites belong to the same family as spiders and ticks. They measure just 0.2-0.3 mm, with 50 fitting on a single pinhead. They live for 65–100 days, and females lay 60–100 eggs in their life.

House dust mites love temperate climates and humidity. They feed off the skin cells we and animals shed, as well as mould, which they digest using special enzymes. These enzymes are excreted in their poo about 20 times a day. They also shed fragments of their exoskeletons.

All these fragments trigger allergies in people with this type of allergic rhinitis (which is also known as hay fever)

What are the symptoms?

When people with house dust mite allergy inhale the allergens, they penetrate the mucous membranes of the airways and eyes. Their body recognises the allergens as a threat, releasing chemicals including one called histamine.

This causes symptoms including a runny nose, an itchy nose, eyes and throat, sneezing, coughing and a feeling of mucus at the back of your throat (known as a post-nasal drip).

People with this type of allergy usually mouth breath, snore, rub their nose constantly (creating a nasal crease called the “dust mite salute”) and have dark shadows under their eyes.

House dust mite allergy can also cause poor sleep, constant tiredness, reduced concentration at work or school and lower quality of life.

For people with eczema, their damaged skin barrier can allow house dust mite proteins in. This prompts immune cells in the skin to release chemicals which make already flared skin become redder, sorer and itchier, especially in children.

Symptoms of house dust mite allergy occur year round, and are often worse after going to bed and when waking in the morning. But people with house dust mite allergy and pollen allergies find their year-round symptoms worsen in spring.

How is it diagnosed?

House dust mite allergy symptoms often build up over months, or even years before people seek help. But an accurate diagnosis means you can not only access the right treatment – it’s also vital for minimising exposure.

Doctor and nurse practitioners can order a blood test to check for house dust mite allergy.

Alternatively, health care providers with specialised allergy training can perform skin prick tests. This involves placing drops of the allergens on the arm, along with a positive and negative “control”. After 15 minutes, those who test positive will have developed a mosquito bite-like mark.

How is it treated?

Medication options include one or a combination of:

• daily non-sedating antihistamines
• a steroid nasal spray
• allergy eye drops.

Your health care professional will work with you to develop a rhinitis (hay fever) medical management plan to reduce your symptoms. If you’re using a nasal spray, your health provider will show you how to use it, as people often use it incorrectly.

If you also have asthma or eczema which is worsened by dust mites, your health provider will adapt your asthma action plan or eczema care plan accordingly.

If you experience severe symptoms, a longer-term option is immunotherapy. This aims to gradually turn off your immune system’s ability to recognise house dust mites as a harmful allergen.

Immunotherapy involves taking either a daily sublingual tablet, under the tongue, or a series of injections. Injections require monthly attendances over three years, after the initial weekly build-up phase.

These are effective, but are costly (as well as time-consuming). So it’s important to weigh up the potential benefits and downsides with your health-care provider.

How can you minimise house dust mites?

There are also important allergy minimisation measures you can take to reduce allergens in your home.

Each week, wash your bedding and pyjamas in hot water (over 60°C). This removes house dust mite eggs and debris.

Opt for doonas, covers or quilts that can be washed in hot water above 60°C. Alternatively, low-cost waterproof or leak proof covers can keep house dust mites out.

If you can, favour blinds and wood floors over curtains and carpet. Dust blinds and surfaces with a damp cloth each week and vacuum while wearing a mask, or have someone else do it, as house dust mites can become airborne during cleaning.

But beware of costly products with big marketing budgets and little evidence to support their use. A new mattress, for example, will always be house dust mite-free. But once slept on, the house dust mite life cycle can start.

Mattress protectors and toppers commonly claim to be “hypoallergenic”, “anti-allergy” or “allergy free”. But their pore sizes are not small enough to keep house dust mites and their poo out, or shed skin going through.

Sprays claiming to kill mites require so much spray to penetrate the product that it’s likely to become wet, may smell like the spray and, unless dried properly, may grow mould.

Finally, claims that expensive vacuum cleaners can extract all the house dust mites are unsubstantiated.

For more information, visit healthdirect.gov.au or the Australian Society of Clinical Immunology and Allergy.