Dust Mites: What Do They Need to Live?

Circadian: Take the case off your pillow tonight and hold the pillow up to the lamp. You won't see a thing. But when researchers tested beds in eight hundred and thirty-one American homes, they found dust mite allergen in about eighty-four percent of them. So what does a dust mite need? Food, warmth and damp air, and the damp air decides almost everything, because a dust mite can't drink. So the drier the air at your pillow stays, the harder life gets for them.

Circadian: We sell pillows, so weigh what we say, but most of this story is about the mite, and the mite doesn't care who made your pillow. Dust mites are tiny relatives of spiders. You'd need a microscope to see one. They don't bite, and they don't live on you. They live in the dust of your bed, and they eat the flakes of skin we all shed every night, which, if you think about it for too long, is a lot of skin. So why do people sneeze? For most people with a dust allergy, the trouble is what mites leave behind, because their droppings carry the allergen.

Circadian: Now picture your bed in the middle of the night. It's warm, there's a fresh supply of skin, and you've been breathing damp air into the pillow for hours. Sounds perfect, right? Most nights, it is. A dust mite's body is about three quarters water. And there's no puddle in your pillow. So where does the water come from? It pulls water vapor straight out of the air, using a salty fluid it makes in glands near its front legs, and once that fluid has soaked up moisture from the air around it, the mite swallows it.

Circadian: Which means its whole water supply depends on how damp the air is. Above about sixty-five to seventy percent humidity, it can take in enough water to make up for everything it loses. Drop the air to fifty percent or lower, and an active mite doesn't last more than six to eleven days. Six to eleven days. That's it. You're probably thinking, fine, so dry the air out and they're gone. Not quite. One young stage of the mite can wait out a dry spell for months and then get going again when the air turns damp.

Circadian: So a dry weekend doesn't do much. The dry spell has to last. And it's not only about survival, because mites also eat more, breed more and leave more droppings when the air's damp, so a damp bedroom means more of the stuff people with a dust allergy react to. In our opinion, this next study is the clearest answer anyone's got. Researchers followed homes through two humid summers. One group kept the air in the house under fifty-one percent humidity, mostly with a dehumidifier and air conditioning.

Circadian: The other homes either ran air conditioning without getting that low, or opened the windows. Everybody kept cleaning the way they always had. In June, the dry homes started with about four hundred live mites in every gram of dust. Seventeen months later? About eight. Four hundred, down to eight. Work that through, and it's roughly one mite left for every fifty that were there, and the allergen in those homes ended up more than ten times lower than in the humid ones, which is a big change for something as plain as a dehumidifier.

Circadian: They kept the air dry. Your pillow sits right where you breathe out, all night, every night. You breathe warm, damp air into it for eight hours, and your head and neck sweat into it too, so a pillow is where a bed gets damp first. In one study, researchers put a brand-new synthetic pillow and a brand-new feather pillow side by side on twelve beds. After a year, the synthetic pillows carried about three times as much mite allergen as the feather ones.

Circadian: How much each pillow picked up also followed how much the mattress under it already had when the study started. So a pillow picks up whatever the bed around it already holds. That national survey pointed the same way. Beds had more mite allergen in older homes, in homes with a musty smell, and in bedrooms with higher humidity. And just under half of the beds carried more than the level researchers use as a benchmark for becoming sensitized. Nearly half.

Circadian: This part is about what we make, so it's our side of it. Every Circadian pillow has a removable organic cotton cover that you can wash in cold water as often as you like. It's the most useful single thing you can do about allergen buildup in any pillow. Inside, wool is the fill we point people with allergies to. Wool pulls up to thirty percent of its own weight in moisture off your skin, and the heat leaves with the damp, so you sleep cooler. That same pull keeps the air right at your face below the humidity dust mites need.

Circadian: The wool carries no chemical finish to wash out or off-gas, because the work is done by the fiber itself. Would you rather have soft? Kapok's our other pick. Mold and dust mites both need moisture, and kapok's waxy fiber sheds water instead of holding onto it. Here's where a pillow runs out, though. If your bedroom sits at seventy percent humidity all summer, the mattress and the carpet stay damp enough for mites. That's a job for a dehumidifier. No pillow can do it.

Circadian: Get a cheap hygrometer, the little humidity meter, and leave it on your nightstand for a week. If it reads over fifty percent most nights, that's the number to work on, and the fix is the one the dry homes in that study used: air conditioning or a dehumidifier, running through the humid months. Wash your pillow cover and your sheets often. Then check the meter again. So what does your bedroom read at night: under fifty percent, or over?