Dampness, Dust Mites and Mold

When travelling this week, I was reading the latest Indoor Air journal and there were two interesting articles that both studied the relationship between mold and dust mites.

The first article was titled, A comparison of the allergic responses induced by Penicillium chrysogenum and house dust mite extracts in a mouse model _1.  Lab mice were exposed to varying concentrations of extracts from house dust mites and the mold Penicillium chrysogenum.  Here is a quote from the article,

“Our data suggest that Penicillium chrysogenum is a robust allergen and may be a more potent allergen source than house dust mite in this mouse model…   P. chrysogenum as well as other molds may play an important role in asthma development in our society.”

Although the article doesn’t address setting acceptable exposure levels for humans, the article shows the dose response figures for mice based on several health outcomes.

The second article I read that addressed mold and dust mites was A dose-dependent relationship between the severity of visible mold growth and IgE levels of pre-school-aged resident children in Taiwan _2.  I found this to be a fascinating article that wonderfully illustrates the point that it’s not exclusively mold that causes health effects in damp environments.

The study found a statistically significant dose-dependent relationship between severity of indoor visible mold growth and total serum antibody (IgE) levels.  So far, so good.  But when they looked at the specific type of antibodies (as opposed to the total), they didn’t find a correlation with fungal allergens.  They did however, find that dust mite antibodies corresponded with the indoor visible mold growth.

So what was going on?  The authors suspect that the degree of visible mold growth is an indicator of dampness.  The mold itself may not be affecting the children’s health, but the dampness leads to elevated concentrations of other exposures, such as dust mite colonies, that do affect health.  They recommend that studies done on the health effects of mold should control for these other exposures.

So to sum up, the first study found that a common type of mold was a more potent allergen than dust mites.  The second study found dust mites to be causing greater allergic responses than mold.  How can we explain the difference in these conclusions?

1. The first study was done on mice, the second on children.  Mice are different than children (one notable difference… my children are much LOUDER than mice!)

2. The first study exposed mice to equal amounts of Penicillium chrysogenum allergen and dust mite allergen.  But in a typical home, are there really an equal amount?  We can say that Penicillium chrysogenum is more potent gram for gram, but exposure to dust mite allergen may be several orders of magnitude greater.

3. In the second study, although total IgE antibodies were more closely correlated to dust mites, they could not establish solid statistical significance.  Also, they didn’t control for many other common indoor allergens like cockroach, which can be found in damp indoor environments.

Do these studies have anything in common?  Yes! They share the conviction that exposures to contaminants found in damp buildings can illicit a measurable affect on health.  That is a powerful message.

  1. Ward, M. D. W., Chung, Y. J., Copeland, L. B. and Doerfler, D. L. (2010), A comparison of the allergic responses induced by Penicillium chrysogenum and house dust mite extracts in a mouse model. Indoor Air, 20: 380–391. doi: 10.1111/j.1600-0668.2010.00660.x []
  2. Hsu, N.-Y., Wang, J.-Y. and Su, H.-J. (2010), A dose-dependent relationship between the severity of visible mold growth and IgE levels of pre-school-aged resident children in Taiwan. Indoor Air, 20: 392–398. doi: 10.1111/j.1600-0668.2010.00663.x []

Controlling Dust Mites

I often hear people say, “I’m allergic to dust.”  They really mean to say, “I’m allergic to dust mites.”  Or, if you’re an indoor air nerd, you tell the people they are allergic to “terrestrial invertebrate arachnids known taxonomically as Dermatophagoides pteronyssinus, Dermatophagoides farinae or Euroglyphus maynei.”

Dust mites are a concern because they can trigger an allergic reaction in sensitive individuals.  The Third National Health and Nutrition Examination Survey found that 27.5% of the population had a positive skin test response for dust mite sensitivities.  Now for the gross part… the allergic reaction is from allergens in the dust mite feces.  95% of the mite allergen is in the feces which has a mean diameter of 22 microns ± 6 μm (with range of 10 to 40 μm)1.

People come in contact with dust mite allergen via the air or a surface.  Because of the fecal pellet’s size, it isn’t airborne for very long.  Fluffing a pillow with a large number of dust mites will make the allergen airborne, but just for a few minutes before it settles out via gravity.  Dust mites like the ecology of dust, especially where there is a high percent of skin scales (think skin cells from dandruff).  Pillows, mattresses and sofas in front of the TV are good habitats.

There are a lot of ways to control dust mites.   Continue reading

  1. Tovey ER, Chapman MD, Platts-Mills TAE. Mite feces are a major source of house dust allergens. Nature. 1981;289:592–593 []

Increased mold levels coming?

Alternaria spores

Can increased levels of atmospheric carbon dioxide (CO2) have an effect on mold spore levels? A new study suggests that increased CO2 will, in fact, lead to a greater number of mold spores outdoors with a resulting effect on allergies. As CO2 levels rise, can we expect to see more allergies to mold?

The article describing the research is titled “Elevated Atmospheric Carbon Dioxide Concentrations Amplify Alternaria alternata Sporulation and Total Antigen Production” and is found in this month’s Environmental Health Perspectives. The researchers were looking at just one species, Alternaria alternata, so we need to be cautious about drawing big conclusions from such a small study (sorry about the sensationalist blog title!). Continue reading