Allergy Plus

Common Irritants

There are over 800 species of mites, of which about 50 can be found in major numbers indoors if suitable conditions are present.


The indoor mites that are considered in connection with dust borne respiratory allergy can be divided up into three main groups: house dust mites (80%), glistening mites (10%) and storage mites (10%). These mites have some uniform characteristics, they are very small, measure about 0.1 to 0.6mm, are whitish in color and cannot be seen to the naked eye.


The house dust mites have specialized in breaking-down epidermal material from animals. Our dust mites feed on scales from our pets and us! – they prefer older scales, as it seems that these are pre-digested by fungi or the mites themselves digest the fungi cells, as the dependence of mites on fungi is shown as mite numbers are decreased by using fungicide on their habitats.


Adult mites are found as males and females, which mate. Fertilized females lay a couple of eggs a day in some few days or weeks before they die. Small six legged larvae hatch from the eggs. When the larvae has been active and eaten for some time it will enter a recumbent position of ecdysis, after which an eight legged protQ-nvmph appears, which likewise finishes in a state of ecdysis. Then this becomes a larger nymph developing through one more recumbent position of ecdysis into an adult female or male.


Much simplified, it can be said that it is mostly temperature that decides how quickly mites can develop, whereas humidity determines the number of house mites that are able to live in a home. In practice both factors work together and are virtual, never constant In culture tests it can be seen that these mites develop their populations most quickly at 25degree and 75% RH. However, house mites have no special humidity preference, but prefer the most humid place when having the opportunity to choose them. It is probable that the relations of the active stages to air humidity in reality it’s to the growth rate of the fungi fed on by mites – the fungi that attack scales. Owing to this and because the single stages to a different extent can endure drier air, there is no sharply indicated lower humidity limit where mites cannot survive, but rather a major margin where conditions gradually become worse. As a rule of thumb, it is said that viable populations are not seen below 65% RH, but the percentage has to drop to 45% RH if you want no mites at all.