What are house dust mites?

House dust mites (Dermatophagoides pteronyssinus, the European house dust mite, or Dermatophagoides farinae, the American house dust mite) are small arachnids (meaning they have eight legs and are related to spiders and scorpions). They measure approximately 0.5 mm long and 0.2 – 0.3 mm across when they are fully grown and are a creamy blue colour. Because they are so small, they are easily moved by small air currents which we generate when moving around the house or doing ordinary household activities.

House dust mites feed off organic dust and detritus that is commonplace in most houses. Examples of such detritus are flakes of dead skin which we are constantly shedding. We shed around 1.5 grams of skin every day, which is enough to feed over one million house dust mites. Their faeces are covered in a film and can contain undigested food, and they will excrete some enzymes out with this, enabling them to come back and re-eat the same piece of food. These dung pellets are extremely light and can remain suspended in the air for up to 20 minutes if undisturbed. House dust mites eat skin flakes, insect flakes, plant material, pollen, and bacteria. House dust mites do not bite, and cause no problems for humans other than allergies.

It takes 30 days for a baby house dust mite to reach adulthood, and it will pass through several stages in doing so. Their lifespan is 2 – 3 months. A mated female can lay 10 – 20 eggs per week, meaning that they reproduce quickly enough to impact on human health. In a week, one house dust mite can produce 200 particles of excretion and even more dust particles which can be covered by enzymes from its gut.

House dust mites are easily killed by temperatures greater than 60 degrees Celcius or less than 20 degrees Celcius. They can also be killed by a relative humidity of less than 50 %. A temperature of 25 degrees Celcius and a relative humidity of 75 % is ideal for reproducing. Human behaviour can generate humidity and temperatures needed for them to survive – heating systems in our houses can provide a nice temperature for them to thrive in and we can contribute to humidity by sweating or from the water vapour in our breath. Prior to the invention of heating systems for houses, house dust mite allergies were rare as house dust mites could all be killed in winter. House dust mites can survive well in many household items of furniture, such as mattresses, chairs, curtains, carpets, as well as soft toys. House dust mites have hooks and suckers on their feet, enabling them to climb and colonise a variety of different surfaces.

House Dust Mite allergies Guide Index:

• What are house dust mite allergies?
• What are house dust mites?
• What are the symptoms of house dust mite allergy?

• How can house dust mite allergies be prevented?
• Are there any medications that can help with the symptoms of a house dust mite allergy?
• What else could be causing my symptoms?