What are dust mites, why do they cause allergies and we can get rid of them?

2021-10-11

As the weather warms, it’s time to open the windows and put away your winter woollies for another year.

If you’re extra keen, you may even decide to do a deep clean in an attempt to wage war on one of life’s annoying realities: dust mites.

These microscopic bugs can cause allergic reactions such as sneezing, wheezing and itching.

Just why some people get affected and others don’t is still a mystery, and there are a lot of myths about how to control them.

So before you launch into your spring dust-busting mission, let’s get down and dirty with the bugs themselves.

What are dust mites?

Dust mites are tiny arachnids, closely related to ticks.

Only around a third of a millimetre long, these white spider-like bugs are everywhere.

“You’ll find them in carpets and beds and in your clothing, but as far as we know they don’t live on your skin,” says Euan Tovey of the Woolcock Institute of Medical Research, who studied dust mite allergies.

Instead, they feast on dead skin cells, which make up a fair whack of house dust.

“When you wash your clothes, the reason the water goes cloudy is it’s your skin cells floating around,” Professor Tovey says.

“We shed about a teaspoon of skin a week.”

What is dust and where does it come from?

As they munch away on the dead skin cells, the mites release enzymes in their gut that break the cells down.

In the 1980s, Professor Tovey discovered one of these enzymes is a powerful allergen that floats in the air on the mite’s poo.

“That allergen from the poo becomes distributed onto smaller dust particles,” Professor Tovey says.

“[These particles] go down to less than a millimetre, so it means they are inhalable.”

People can also be allergic to a number of other proteins in the mite’s body, but the enzyme accounts for about 60 per cent of allergies.

That’s because a mite can produce a lot of poo over its lifetime of up to 90 days.

“A lifetime of poo is much more than a mite body, because they are continually producing poo.”

Dust mite allergens can also hang around for a long time, depending on the level of humidity.

“In dry conditions it will hang around for years, under moist conditions it will break down in months.”

Are some times of year worse than others?

The amount of mite allergen fluctuates through the year, depending upon the season.

“The growth conditions for mites is pretty ideal in spring because they like 25 degrees Celsius and pretty high humidity of around 75 per cent,” Professor Tovey says.

The hotter and more humid the weather, the better, but our homes provide the perfect environment for them to thrive all year round, even in arid areas.

“There are little wet places in houses, like the bottom layer of carpet is pretty damp, and beds have damp patches because of condensation … so you’ll get dust mites all the way out to Broken Hill,” Professor Tovey says.

But even though dust mite numbers boom at this time of year, exposure to the allergen is greater during winter when your house is shut up.

Why are some people affected by dust mites and others aren’t?

Dust mite allergens can cause conditions such as hay fever, eczema and asthma.

But the big question is why some people become allergic to mites and some people don’t.

We used to think that the more exposure that someone had to mites, the worse their allergy, but that has turned out not to be the case, Professor Tovey says.

“There is a huge paradox about dust mite exposure,” he says.

Nobody knows why some people are more allergic than others, says Wayne Thomas, of the Telethon Kids Institute, who has studied dust mite allergens.

Professor Thomas says some studies indicate that respiratory infections may trigger allergic reactions.

“It might be a matter of timing; whenever you get your big hit of dust mite allergen exposure compared to when you last had a [respiratory] infection could be important.”

Bacteria in your gut may also influence whether you become allergic or not, he added.

Diagnosing dust mite allergies is tricky.

“The standard test that doctors like to do with the skin prick test is far too sensitive,” Professor Thomas says.

What’s in our household dust?

He estimates about 75 per cent of people who test positive to dust mites have very low levels of sensitivity, or are reacting to different factors in the environment.

But for people who are sensitive to dust mites, the news is not good.

“Our ability to treat it hasn’t got much better in the past 30 years or so,” Professor Thomas says.

Even though we’ve identified the main allergens, we still don’t understand much about what they do in the human body, and why different people are allergic to different dust mite allergens.

“If we want to make a better treatment for therapy or [develop a vaccine], we have to use the allergens we think cause all the allergic response,” he says.

Are some parts of the house worse than others?

We once thought that we mainly got exposed to dust mite allergen in bed, but experiments by Professor Tovey have shown we get exposed whenever we move.

“Any time you move, you’re generating your own little personal cloud of dust.”

Just like Pig Pen from Snoopy, you are surrounded by a cloud of dust when you move.(Gfycat)

The studies show that you stir up dust when you first get into bed, but that generally settles down until you roll over.

“If you’re a restless sleeper you probably get more exposure,” he says.

But you are also exposed during the day.

“It comes off your clothing, it comes off when you sit down on the sofa, and when you walk across the carpet.”

And beware if you are planning to take clothes out of storage.

“They have probably the highest levels of allergen I’ve ever seen,” Professor Tovey says.

“If you put them on or you shake them around, if you are a bit allergic to dust mites you can certainly develop some sniffing and sneezing.”

What’s the best way of reducing dust mite allergens?

While you can never totally get rid of them, there’s a few things you can do to lower your exposure.

The simplest thing is washing.

“Dust mite allergen is incredibly soluble, it dissolves like the click of your fingers,” Professor Tovey says.

“Warm water is better than hot, detergent is better than not.

“If you use really hot water, which is really hard to do, you can kill the mites, but they’ll still come back from somewhere else.”

Keeping your home dry will also keep dust mite and allergen levels low.

Airing clothes and carpets in sunlight can also kill dust mites, but you won’t get rid of the allergen unless you wash the items first.

Using a wet cloth to dust may help to reduce the allergen slightly.

Professor Tovey says vacuuming will also help to reduce allergen a little bit on surfaces, but “it’s not great”.

“There’s still a lot that exists after you vacuum a floor pretty thoroughly, there’s still a lot of material in the base of the carpet,” he says.

There is little evidence to recommend special mattress encasings, as they don’t stop dust mites in other areas.

“You can spend a vast amount of money on better vacuum cleaners and mattress encasings, but you can achieve a lot of that purpose just by regular washing,” Professor Tovey says.

And forget the special sprays.

“Once you kill a few mites, some others are just going to replace them, so I would say it’s a bit of a futile exercise,” he says.

“Even if they do kill mites or destroy allergens a little bit, do they really make people better?

“I’m very confident there’s no decent data showing that.”

abc.net.au, 11 October 2021
; https://www.abc.net.au