Particulate matter is a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.

These particles come in many sizes and shapes and can be made up of hundreds of different chemicals.  Particle pollution includes:

  • PM10 : inhalable particles, with diameters that are generally 10 micrometers and smaller; and
  • PM2.5 : fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller. The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle.

Particulate matter contains microscopic solid or liquid droplets that are so small that they can be inhaled and cause serious health problems. Particles less than 10 micrometers in diameter pose the greatest problems, because they can get deep into your lungs, and some may even get into your bloodstream. 

Indoor air particulate matter comes from both the outdoor air and the activities in the home.   Outdoor sources can include, but not limited to, pollens, mold spores, and dirt.   Indoor sources can include, but not limited to, molds, pet dander, dust mites, and dust.  Many of these substances are allergens.     

Particulate Matter Health Effects

Many indoor air quality hazards have unknown, but suspected health effects. Outdoor particulate matter has been evaluated by the US EPA for decades and thus there are some known health effects associated with. There is typically some variation of indoor particulate matter and outdoor, given the types of chemicals and particles found indoors are different from the outdoor. Indoor particulate matter typically includes what is found outdoors locally in addition to other particles. Because of this, it would be logical to assume that the health effects of outdoor particulate matter are still relevant indoors but there may be some variation. Particulate Matter is known to impact the cardiovascular system along with the respiratory system.     A study conducted showed more than 130,000 deaths attributed to outdoor Particulate Matter during one year (2005).   There is a positive correlation between emergency room visits and increased particulate matter. There are no standards set for indoor particulate matter count.  


The word allergy is defined in medical dictionaries as “a hypersensitive state.”

The leading cause of non-atopic allergies in adults and children is overexposure according to the American Academy of Allergy, Asthma & Immunology.

An allergen or sensitizer is capable at very small concentrations of inducing excessive immune responses in a genetically predisposed individual. Allergy is in this way a heritable trait. Not everyone has the genetic predisposition toward the development of allergy antibody immune responses to sensitizing agents, or allergens.

A survey conducted by the National Survey of Lead and Allergens in Housing (NSLAH) found that exposure to multiple allergens was common in US homes. Of the surveyed homes, 51.5% had at least six detectable allergens and 45.8% had at least 3 allergens exceeding increased levels. The conclusion of the study found that increased allergen levels in the home are associated with asthma symptoms in allergic individuals.

Allergies account for a significant amount of missed days of work and school and has tremendous impacts on the quality of life.  The health effects of allergies are well beyond a runny nose or watery eyes.