House dust mites have been recognised as a major source of allergen. Three members of my family are seriously affected.  Because we have wall-to-wall carpets, soft furnishings, and central heating in our homes, the density of house dust mites in our homes has increased dramatically. Over 80% of young adults and children with asthma are hypersensitive to its allergens. I’ve been finding out some facts about this.

The house dust mite is common: The concentration of the main allergen protein, Der p1, can outlast the mite itself, because it is found in high concentrations in mite faeces. In 1991, 40 houses in south Manchester were studied for concentrations of the Der p1 allergen [1], in dust collected from bedroom and living room carpet, and from mattresses. Concentrations varied widely between houses, without much variation with season. Concentrations in dust taken from mattresses and carpets were in the range of about 0.5 to 200 µg/gram of dust.

Getting rid of the mites: A number of methods has been tried, including using mite-killing chemicals and liquid nitrogen (the mites are killed by freezing). The problem is that these methods may kill the mites, but the Der p1 allergen that has collected is still there.

Steam cleaning in the home: The field trial was carried out on a ground floor tenement in Glasgow which was 100 years old, but with central heating. Carpet areas in bedrooms, living room, kitchen and hall were delineated with masking tape. The carpets were about 15 years old. Dust samples were taken from each area, and then one area steam cleaned while another was left untreated. When carpets had dried, another dust sample was taken from each area.

There was no difference in the concentration of Der p1 in dust samples of untreated carpets, but in those which had been steam cleaned there was an average 87% fall in the concentration of Der p1, from 3.3 µg/gram of dust to 0.44 µg/g. But some areas had low concentrations of allergen to begin with, and there were some quite dramatic falls in the areas with the highest concentration.

So if you've got carpets, and problems with allergy in a family member, then it is worth remembering that steam cleaning removes the allergen as well as killing the mites.