Getting to know

HDM are tiny, spider-like creatures that thrive and multiply in the dust inside the house. They are transparent and measure 0.3 mm, therefore they cannot be seen with the naked eye.

Mites can grow not only indoor but also outdoor. However, allergy is caused in the vast majority of cases by two kind of mites growing indoors, Dermatophagoides pteronyssinus and Dermatophagoides farinae. This is are very complicated names that you don’t need to know but knowing their meaning will help you understand mite’s habits: Dermatophagoides means “the one that eats skin”. 

Don’t get scared, HDM do not eat living skin of your body and you will never get attacked by them. They eat only dead skin cells that have detached from our body and which they can find abundantly in the house dust. Indeed skin, like any other organ in our body is constantly renewing its cells. In fact the skin is formed by several layers of cells: the bottom ones are living cells while the superficial layers of cells are formed from dead, dry cells. These cells detach constantly from our body, especially when the skin is rubbed (for example by the clothes we are wearing, when we are lying in bed or sitting on chairs or sofas). Finally these skin scales will end in the house dust, providing food for the house dust mites.

The skin scales are big and tough and therefore it is hard for the tiny mites to digest them. Consequently in order to be able to eat, the mites have to “prepare” their food first: they engulf the skin scales and inside their digestive tract they cover them with digestive enzymes and with a membrane layer creating what is known as a “digestion cocoon”. These cocoons are then voided to the outside and the digestive enzymes enclosed are let to finish the digestion process (they are melting the hard cover of the skin scales rendering them soft and easy digestible).

Why is this important? Because in fact it is not the house dust mites themselves that we are allergic to but the digestive enzymes from these digestion cocoons. How do they get outside the cocoons? Sometimes they simply pass through the wall of the cocoons which are not 100% impermeable. Also the enzymes are released if the cocoons are broken (which is happening very often when we are cleaning the house). 

It is not only food that house dust mites need for thriving. They also need water which they take from the air and a warm environment. Consequently they grow especially in the areas with high (>75%) air humidity and temperatures around 25°C.

Our bed is the place with the highest concentration of house dust mites in the house. Why the bed? During the sleep a large quantity of skin scales are removed from our body (due to the rubbing of the skin against the sheets when moving in bed) and are dropped in the mattresses, pillows and duvets, providing thus a huge reservoir of food for the mites. Also when we are in bed perspiration and the heat of our body provides both adequate humidity and warmth for house dust mite thriving.

Other important house dust mites reservoirs are carpets  and furniture upholstery,    curtains, floorings and generally all other places where house dust accumulates.

Similar with all airborne allergens house dust mite cause primarily respiratory allergies. Because house dust mite allergens are very small, when we inhale them a large proportion will be able to escape nose filtering and landing inside the bronchi. Consequently most often they cause asthma and allergic rhinitis (either alone or in association). 

House dust mites are also a frequent cause of allergic conjunctivitis. 

Also, even though more rare, they can be a triggering or aggravating cause of atopic dermatitis.

As with the other airborne allergens, it is practically impossible to avoid completely house dust mite contact and also exposure reduction implies it is quite difficult. There are however measures that can help you in this task.

As the bed is the most important reservoir of house dust mite allergens and we spent more time in our bedroom than in any other room of the house it is very important to try to reduce allergen concentration in this room. Bellow you can find some tips that might help you in achieving this goal: 

DO… Use plastic or mite resistant covers for your bedclothes and the mattress If you don’t have mite resistant mattress covers vacuum the mattress thoroughly every week Use blankets, duvets and pillows made of synthetic fabrics (not feathers) that can be washed in hot water (>60°C) Change bed linen at least 1/week Wash bed linen at high temperatures (>60° C) Air your bedclothes daily or at least 2-3 times/week (during the summer days leave them in the sunshine for a few hours) Remove carpets (especially wall-to-wall carpets), curtains, up-holstered furniture from your bedroom Best solution is to leave your floor uncovered. Hard, uncovered floors (wooden, linoleum or ceramic tiles) can be easily cleaned

DON’T… Don’t make your bed as soon as you get up (let the bedclothes to dry and cool out after the night sleep) Don’t heat your sleeping area (certainly not above 21-22°C) Don’t humidify the air in the house and particularly in your sleeping room Don’t sleep with cuddly toys made of soft fabrics Don’t do the house cleaning