They prowl our beds and sofas, invisible to us, but hugely allergenic. Here’s the latest on dust mites, and what you can do to protect your family. First published in Allergic Living magazine; to subscribe click here.
They’re tiny enough that you can’t even see them with the naked eye – but as millions of people around the world can attest, dust mites pack a big wallop when it comes to allergies and asthma. In fact, it’s estimated that 84 percent of U.S. homes contain dust mite allergen, and it’s one of the most common and potent allergy and asthma triggers.
So what exactly are these little freeloaders? Why do they love us so much? How come they make us so miserable? And most importantly, which ways of getting rid of them actually work? You might be surprised.
The Mite Life
Some medical websites claim that dust mites are so tiny, there can be as many as 40,000 of them in a single speck of dust. But that’s far from the truth, according to Dr. Jay Portnoy, director of allergy, asthma and immunology at Children’s Mercy Hospital and professor of medicine at the University of Missouri in Kansas. Portnoy, who recently co-authored extensive new guidelines for physicians who treat dust mite allergies, says the mites are small, but they are almost the same size as many dust particles. In fact, they are just outside our range of vision so they can be seen with even the most basic microscope.
While they look like they could be distant relatives of the beetle, dust mites are not actually insects; they are arachnids with close biological ties to spiders, crabs and shrimp. But unlike their web-building and seafaring cousins, dust mites’ favorite food is skin scales, which is why they flock to mattresses, carpets and upholstered furniture where people’s dead skin tends to accumulate. (Their scientific name is Dermatophagoides, which means “skin eating.”)
Dust mites live roughly two to four months, and are hungry for moisture; in fact, they need a steady supply in order to survive. By weight, dust mites are roughly 75 percent water, and they can’t drink, so they rely entirely on absorbing moisture from the environment around them through glands at the base of their front legs. That’s why in dry climates, dust mites are almost nowhere to be found – even in dusty spaces.
“They’re basically bags of water with legs, so they don’t tolerate drying out,” says Portnoy, who worked with 22 other top experts to produce Environmental Assessment and Exposure Control: A Practice Parameter, Dust Mites for physicians. “So it can be very dusty in Denver, but they don’t have any dust mites because it’s persistently so dry that dust mites don’t survive. In Florida it’s so humid that you can’t get rid of them. They’re everywhere.”
In most climates, mite populations increase in summer, when humidity is high, and peak in the fall – which experts suspect is part of the reason asthma rates are so high at that time of year. They begin to taper off in winter when it’s colder and drier. By late winter and early spring, populations are usually at their lowest.
So What’s the Problem?
They also poop a lot – roughly 20 times a day – and those fecal pellets are the major source of the powerful allergens they produce. The tiny pellets are just the right size to become easily airborne, too, so even walking across a carpet, sitting on a sofa, or moving a pillow can send them flying – and into people’s airways. Once the pellets get kicked up, they don’t settle back down for 15 to 30 minutes.
“When mites eat skin cells, they have enzymes they use to digest them. And when the little fecal pellets come out, the enzymes are in those pellets and they serve as very potent allergens,” says Portnoy. “And when you inhale it’s just the right size to get deep into the lungs and cause an asthma attack.”
But the little pests aren’t only causing problems with the air we breathe; in rare instances they have also stirred up trouble with our food. Dust mites and other types of allergen-producing mites can contaminate grain flour, and systemic reactions from hives to anaphylaxis have been reported in dust mite-allergic people after eating pancakes, grits, beignets and other grain-containing foods.
The allergens are so stable that cooking doesn’t help; as a result, Portnoy recommends that people with mite allergies keep their flour in sealed plastic containers – and that people who experience allergic reactions to grain flour, but test negative for allergy to the grain, should also be tested for allergy to mites.
There’s also an intriguing shellfish link: tropomyosin, one of the major allergenic proteins in dust mites, is also present in shrimp, lobster and crab. A few studies suggest an allergy to dust mites may make some individuals more susceptible to reacting to a crustacean dinner. But the connection is unclear, and the new guide- lines don’t recommend avoiding shellfish simply because of a dust mite allergy. Allergists point out that dust mite allergy is far more common than shellfish allergy, so one does not necessarily lead to the other,
Next: How to Get Rid of Them