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Environmental Relative Moldiness Index (ERMI)

What is ERMISM?

ERMISM stands for Environmental Relative Moldiness Index. It’s a standardized scale developed by the U.S. Environmental Protection Agency (EPA) based on a national database of approximately 1,100 homes sampled by HUD during the 2006 American Healthy Home Survey. Samples were analyzed using Quantitative Polymerase Chain Reaction (QPCR) techniques.

ERMISM provides an objective, DNA-based method for assessing mold in homes. Traditional mold testing often relies on air sampling or culturing spores on media, which has limitations. ERMISM, in contrast, uses Mold-Specific QPCR (MSQPCR) to detect and quantify mold DNA sequences down to the species level.

How Was ERMISM Developed?

EPA scientists compared mold concentrations between “moldy homes” (with visible mold or past water damage) and “reference homes” (with no visible mold). They then divided molds into two groups:

  • Group 1: Mold species more common in moldy homes
  • Group 2: Mold species commonly found in all homes

For each ERMISM score, log-transformed concentrations of Group 2 are subtracted from Group 1. This provides a relative moldiness index score for the home.

The Collection Process

Dust samples are typically taken from carpets, which act as a historical reservoir of airborne mold spores. Other surfaces like drapes, furniture, or HVAC ductwork can also be sampled, but carpet sampling is the standard method.

We collect a composite sample from two locations: a 3 ft. x 6 ft. area in front of the most-used sofa, and a similar area in a bedroom. These combined samples offer the most accurate representation of overall mold levels in the home.

Advantages of ERMISM

  • Species-level identification of mold types
  • High sensitivity — detects even low levels of spores
  • Captures total mold cell content, not just spores
  • Fast turnaround — results typically available in 24 hours
  • Machine-based, standardized analysis reduces human error

What ERMISM Is Not

ERMISM measures mold levels, not health effects. Individual responses to mold exposure vary based on age, health conditions, and genetics. Only medical professionals can assess health risks related to mold exposure.