Dust mites are microscopic organisms that live on human skin scales, which we shed off regularly. They are commonly found on pillows, mattresses, upholstered furniture and in clothes changing areas. This organism is responsible for most of the year-round type allergic rhinitis.

Quantities of household dust vary enormously depending on where the house is located, the climate, altitude, the time of year, etc. They also vary from house to house (a farm is different from a city flat), and within the same house (a bathroom is not a bedroom).

There is however one thing that never varies: household dust is a complex reservoir of allergens. The main allergen is the house-dust mite.


Mites, or acarids, are tiny, spider-like creatures only about 0.3 millimetres long. They are therefore invisible to the naked eye. Two species which live in household dust are very important in respiratory allergies: Dermatophagoides pteronyssinus and Dermatophagoides farinae to give them their Latin names.

Dermatophagoides mites feed on human scales or flakes which shed from the skin. They are found mainly in bedding (pillows, mattresses, eiderdowns, etc.) because this is where we lose the most scales (our skin rubs against the sheets). Feeding on shed skin is not enough for these mites. They also feed on a microscopic fungus (mould) which grows mainly on mattresses.

To complete this delightful picture, it may be interesting to know that people with mite allergy are not allergic to the mites themselves, but to their…droppings. Mite excreta seem to be highly allergenic.

Mites are much more numerous in bedding than on the bedroom floor. One gram of dust taken from a mattress could contain anywhere from 2,000-15,000 of them!

When you sleep on a mattress, the temperature (between 20°-30° C) and relative humidity (dampness) created by your body provide ideal conditions for these unsavoury little creatures to reproduce, as well as ideal growing conditions for the mould on which they feed.

Tip: A fundamental rule

  1. Air out your bed every single day; do not immediately make the bed as soon as you get up.
  2. Even if your bedroom is cool and dry (which would be ideal because too much heat dries out mucous membranes, encouraging rhinitis and asthma), you should nevertheless thoroughly air out the sheets at least twice a week.
  3. Blankets should be made either of cotton or synthetic fabrics that can be washed in hot water (55°C or above). Pillows should be filled with synthetic material, not feathers, and mattresses should be covered with plastic or allergen-excluding material. If the mattress has not been covered, it should be thoroughly vacuumed at least once a week.
  4. Every night while we are asleep, the temperature of our body and our breathing give mites just the right conditions they need to grow and breed. So change the sheets as frequently as possible.
  5. Other rooms in the house should be given equal attention, although not so often. Pay particular attention to floors, armchairs, cushions, curtains and drapes.


Allergy to household dust (especially to mites) can come out as asthma, rhinitis and/or atopic dermatitis (eczema). Flare-ups usually happen just after the sufferer wakes up. Symptoms last all year long but tend to be worse in autumn and winter, when it is wetter.

Above 1500-1800 metres altitude, both types of allergy-causing mites are virtually non-existent. They simply do not like dry mountain climates! Which makes them ideal places for mite-allergy sufferers to live or holiday.

Eviction (getting rid of the allergen) is the best way of reducing or eliminating an allergy to mites. First see to the bedroom, then go to work on the rest of the house.

Making a bedroom or a house “dust-free” means identifying and eliminating any materials where Dermato-phagoides mites could hide and grow.

  1. Replace bedding materials (mattresses, pillows, eider-downs, bolsters) containing wool, kapok, cotton, horse hair, feathers, or down with synthetic materials (foam rubber, polyester, dacron, etc.).
  2. Buy blankets and curtains made of synthetic fabrics.
  3. Remove all down, wincyette, and flannel.
  4. Remove thick throw rugs and animal skins.
  5. Replace fitted (wall-to-wall) carpets and rugs with vinyl or parquet flooring; the room will also be easier to clean.
  6. Get rid of cushions not filled with synthetic materials, as well as anything made of wool or cotton.
  7. Reduce the number of “dust collectors” such as intricate or bulky decorations: heavy drapes, double curtains, tapestries, etc.
  8. Use the vacuum cleaner more often around the house; in particular, vacuum mattresses and bedding thoroughly and regularly (preferably when the allergy sufferer is not there!).
  9. Get rid of green (non-flowering) house plants
  10. Keep teddy bears and woollen toys out of children’s bedrooms.

Vacuum cleaners are now available which, when used with special accessories, are very effective for cleaning mattresses. The best ones have a filter which prevents exhaust air from blowing dust into the room.

Tip: Avoid unnecessary costs!

Hypo-allergenic materials which are impenetrable to house-dust mites are useful for covering
mattresses, duvets or pillows, but they can be expensive. Obviously, they will only help persons allergic to mites, not with other allergies!


Mildew is a kind of filamentatious fungus. Their colouring varies from species to species: green or black for Penicillium and Aspergillus, red for Merulius or house fungus. They can be found outside (on rotting vegetation or in the air) as well as indoors.

When they grow, filamentatious fungi produce “spores” (like a seed) as part of their reproduction process. Like pollen, spores are culprits in respiratory allergies (rhinitis and allergic asthma). Also just like pollen, the atmospheric spore count depends on weather conditions (maximum at times of year when it is hot and humid).

Tip: How to avoid mildew

Around the house:

  1. Frequently air out places where mildew tends to grow.
  2. Ventilate closed spaces (bathroom, kitchen, laundry, cellars, attics).
  3. Solve problems of dampness (seeping water, rising damp, etc.).
  4. Clean and disinfect air conditioning con-duits.
  5. Do not leave mouldy food lying about.
  6. Watch out for flower pots where the soil is covered with a whitish or orange sub-stance; this could be mildew.
  7. Carefully inspect wallpaper; mildew often grows behind it.

Outside the house:

  1. Don’t walk in wooded areas after it rains or in foggy weather.
  2. Don’t touch bags of dead leaves which were collected several days earlier.
  3. Second homes or houses people seldom live in are often rich in mildew.