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Useful facts on mites (midd)

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What are mites?

Mites are 0.2 to 0.3 mm in length, have eight legs and are most closely related to spiders and ticks. Apart from the fact they easily cause allergies, they are non-hazardous to humans. They do not bite and are not vectors of any kind of infection. They live on skin flakes from people and animals and some species also live on flour dust. A mite has a lifespan of only one month, however the female lays 20-30 eggs at a time, and therefore reproduction may result in large numbers of mites when conditions in the indoor environment are optimum. In Norway the prevalence of mites is highest from November to February, in other words the season during which we spend most time indoors. Mites, as well as keeping domestic animals, are the most important cause of allergic symptoms outside the pollen season.

Who gets mite allergy?

At particular risk are those individuals (especially children) with so-called atopic disease – or with a family history of atopic disease (atopic eczema, hay fever, allergic asthma) and who are exposed to large numbers of mites in the home.

Where are mites found?

Mites will thrive where they find suitable food, the right temperature and slightly raised air humidity (50-80 %). All humans shed such a large quantity of skin flakes in bed that it can feed thousands of mites over several generations. Therefore, the majority of mites are found in the bedroom – and particularly in bedding, mattresses and the bottom of the bed-board. They withdraw to the mattress and bed-board where they reproduce and produce eggs and young. They also do particularly well in carpeted bedroom flooring.

What are the symptoms of mite allergy?

Such allergies often lead to asthma and/or significant problems involving a blocked or runny nose. Allergic eye reactions and some instances of atopic eczema may also be exacerbated by allergy to house-dust mites. Children are particularly vulnerable. If the allergy is left untreated, the mucosa of the eyes, mouth airways and bronchi will become hyper-irritable. This will trigger symptoms, exacerbated by a variety of dusts and odours (irritants).

How is it diagnosed?

The diagnosis can not always be made based on medical history. The fact that many people suffer symptoms at night-time may be for several different reasons. Standard allergy testing is necessary in order to establish whether an allergy to mites exists. Testing is usually performed using preparations derived from the two most important allergy-provoking mites (Dermatophagoides pteronyssinus, D. farinae).  Testing for allergy to dust mites by skin tests or blood tests – sent to a special laboratory – is accurate and reliable. Such tests cannot be used to determine future risk, only to establish whether such allergy has already developed.


Allergy to mites is a global health problem. Studies from several countries reveal that house dust mites are a significant factor in relation to the development of allergy. Thus far there are few research studies which provide any information about the prevalence of dust mites in Norwegian homes.

Countermeasures for mite allergy:

The primary countermeasure where a diagnosis of mite allergy has been made is to reduce the contact with mites. Completely eliminating mites from a house is often impossible. Effective measures for reducing the occurrence of mites include increasing ventilation, reducing the amount of dust by avoiding wall-to-wall carpeting, stuffed mattresses and furnishings and by using a central vacuum cleaner or modern vacuum cleaner with HEPA- or micro-filter.

Mites are killed by extreme cold and heat. On frosty days (-15ºC to -20ºC), mattresses can be placed outside for airing for a day before beating them well and bringing them back in.  Mites also do not survive washing of bedding at 60ºC.

Use of a mattress dust mite cover is a practical means of protecting against allergens in bed. A mattress dust-mite cover locks the mite out, but allows moisture from the body through. Mattress, pillows and duvet covers are covered with an allergen-proof encasing; normal bedding is placed over the cover.

Down or synthetic?

Allergic individuals can also test to see whether fitted sheets, duvet cover and pillowcases intended for individuals with mite allergy, lead to improvement in symptoms. The down-proof twill is a tightly-woven substance, and thereby a mite-safe material. That the bedding tolerates washing or dry-cleaning is more important than whether the content is synthetic or down.

Rebate for dust mite covers:

For children and young people under the age of 16 years with documented mite allergy, a one-off payment can be granted to cover costs for mattress and pillow dust mite covers. The costs can be covered completely with a contribution of up to NOK 1250 (including VAT) for mattress dust mite cover, and NOK 250 for pillow dust mite cover. The covers must be approved by the Norwegian Asthma and Allergy Association. Currently this only applies to dust mite covers from Sleep Scandinavia (tel. + 47 67 11 03 17) who are recommended by NAAF, and approved covers from NorMed AS (tel. +47 67 98 01 00). The covers can be ordered directly from suppliers. These aids should be prescribed by a specialist and the cost paid in advance. Documentation of proven mite allergy and receipt of purchase are to be sent to the national insurance office for refunding. The effects of measures against house dust mites take time to appear (and are not one hundred percent effective). Nevertheless, it would be wrong to believe that medication can replace actions against mite allergy and the two forms of treatment should be combined.

Treatment of mite allergy:

It is important that measures be instigated to reduce growth conditions for mites.
Additionally, medicines are often required to prevent and ease symptoms and illness. Choice of medicines and how they are used must be adapted to the individual, and be decided by the doctor.
In the case of allergy to house dust mites, medicines are often quite effective. If measures are not taken to eradicate house dust mites, there is a risk of worsening of the allergy and reducing the efficacy of any medication used in treating the allergy.

Good advice in mite allergy:

Avoid use of chemicals to eradicate mites.
Change bedding weekly.
Good airing outside. Temperatures in bedrooms should be kept below 18ºC.
Avoid “dust-collectors” such as cuddly animals, open bookshelves, wall-to-wall carpeting, etc.
A useful measure is allowing the bed to remain unmade for a few hours, such that any moisture in the mattress and bedding has a chance to dry out.
If the air humidity can be kept below 40 % RH for three months in the winter, mites usually die out.
Do not use fan heaters, etc., which blow dust into the air.