Strange Bedfellows: Warm Weather Means Dust Mite Population Explosion

May 21, 1997

GAINESVILLE—When it comes to creepy-crawly insect pests that thrive in warm weather, the tiny, almost invisible dust mite can cause big problems around the home, especially for allergy sufferers.

“Just thinking about them is enough to give you the heebie-jeebies,” said Phil Koehler, urban entomologist with the University of Florida’s Institute of Food and Agricultural Sciences. “For some people — especially clean freaks — finding out you’ve got these things living all around you can ruin your whole day. Worse yet, you may be inhaling their droppings.

“These microscopic scavengers, which feed on skin shed by people and pets, are invisible to the naked eye but they can be found even in the cleanest homes,” he said. “A gram of dust may contain up to 4,800 mites, and an ounce of dust may host 136,000 or more.”

Koehler said dust mites can inhabit mattresses, pillows, blankets, quilts, carpets and fabric-covered furniture. The more these items come in contact with people, the more likely dust mites will be present.

They are most prolific in bedrooms where an average bed contains 10,000 dust mites and a 2-year-old pillow can get about one-tenth of its weight from mites, dead mites and their droppings. And carpeting may be home to millions more.

“While they certainly make gross bedfellows, mites are harmless to most people. If you’re not allergic to them, you probably don’t even notice them. You can’t smell them, but they do produce allergens that can trigger allergic uncomfortable reactions in approximately 80 percent of allergy sufferers,” he explained.

Koehler said a protein in dust mites and their fecal matter is the culprit. When this allergen becomes airborne and is inhaled, it can trigger asthma, hay fever or itchy skin reactions. A single mite can produce up to 20 microscopic pellets of fecal matter daily.

Their typical life cycle ranges from 20 to 45 days, with some females laying as many as 80 eggs during this period. (The scientific names for the two most common American house dust mites are Dematophagoides farinae Hughes and Dermatophagoides pteronyssinus Trousessart.)

“Up close under an electron microscope, they’re ugly little creatures and they’ve got sticky little feet that give them the ability to hold on, especially when you’re trying to vacuum them up.”

He said UF/IFAS research has shown dust mites thrive in warm, humid environments. Bedding usually provides these ideal conditions. Research also indicates dust mites will stop reproducing and die if the humidity level is 50 percent or lower. In Florida, humidity levels almost never go below 50 percent during summer months.

Marie Hammer, UF/IFAS home environment specialist, offered these suggestions for battling dust mites:

  • Start in the bedroom where you spend about eight hours a day. She said even new bedding materials marked “allergy free” may quickly accumulate dust and dust mites. “Washing all bedding, including blankets, mattress pads, comforters and pillows, in hot water (130 F) at least once a week is probably the single most important thing you can do,” she said.
  • Using nonallergenic, impermeable covers for pillows, mattresses and box springs also helps. Use fiberfill pillows that are hypoallergenic. Wash pillows or at least put them through the dry cycle to remove dust and allergens. Wash curtains regularly.
  • Use a dehumidifier or adjust the air-conditioning system to keep home humidity at 50 percent or less. Use high-efficiency filters and change them regularly.
  • Vacuum carpets every few days. This may remove some of the dead mites and their droppings, but the live mites will cling to their surroundings. An inefficient vacuum cleaner can make the problem worse by drawing dead mites and their fecal matter out of the carpet and blowing them into the air.
  • Have carpets steam cleaned or chemically cleaned on a regular basis. Consider hardwood floors, tile or other smooth surface flooring instead of carpet. Hanging carpet outdoors in the hot sun will help kill dust mites.