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The goal of PECO has always been to clean the air in a more complete way than traditional filtration. Indoor air quality experts at Florida International University recently published a preclinical study in Nature titled Indoor‑air purification by photoelectrochemical oxidation mitigates allergic airway responses to aerosolized cat dander in a murine model. The team set out to tease apart some of the differences in how air cleaned by Molekule’s PECO technology affects allergic reactions compared to air cleaned by the current gold standard of traditional filtration, the HEPA filter.

The researchers exposed mice to cat dander in rooms cleaned by both a traditional air purifier and a Molekule air purifier with PECO. These two groups were compared to mice displaying symptoms of an allergic reaction to unfiltered cat dander and to healthy mice.

Mammalian immune systems are far more sensitive to free floating allergy triggers than any known analytical method, so the researchers essentially used the mouse immune system to detect what could remain in air that has passed through a HEPA filter. Overall, they found the HEPA filter’s traditional approach to standard particle filtration certainly helped to reduce the allergic impact of the cat dander. However the researchers did find a measurable difference between PECO and HEPA, though real clinical testing will be necessary to know the impact on the human immune system.

While it’s been clear that PECO is capable of destruction at the molecular level since its invention, it’s never clear how quickly or to what degree it destroys a specific substance until some rigorous testing is done. Allergy triggers like cat dander or mold spores are tiny parts of proteins produced by these organisms, so the team also did some experiments at the chemical level to understand how quickly PECO destroys different proteins.

Full-Body Exposure for Six Weeks

Chambers in lab for study

An extract of cat dander rich in Fel d 1 was sprayed into the custom chambers shown above as a fine aerosol three times per week, so the subjects had full-body exposure. Air samples were taken just after spraying and one hour later looking for the specific tiny protein in cat dander that actually triggers the allergy, which has the name Fel d 1. It’s responsible for 90% or more of cat allergies. It’s found in the dander, glands, and saliva of house cats and other related feline species, can trigger an allergic reaction with relatively low amounts, and is implicated in at least 29% of asthma cases. 

As mentioned above, there were four groups analyzed:

  • Allergic: Exposed to unfiltered cat dander. This group represents what a full-blown allergic reaction looks like.
  • HEPA: Exposed to cat dander filtered by HEPA, which can capture 99.97% of the hardest-to-capture particles.
  • PECO: Exposed to cat dander filtered by PECO, which has a lower capture rate but is designed to render allergy triggers into neutral components of the air.
  • Normal: These mice were not exposed to anything. This group represents what it looks like to not have an allergy. 

Note: The PECO-filters used in this experiment were the original Molekule Air Mini+ PECO filters that were rated at MERV 16.

How is an allergic reaction measured?

The team looked at more than a dozen metrics to measure the degree of allergic reaction in each group. Exactly how an allergy works is very complex because the immune system has to be very complex to keep up with all the possible pathogens, venoms, parasites, or anything else that could come along. Most of us are aware that histamine is part of an allergy attack because we know antihistamine medication works to help allergies. The rest of the allergic response can be understood by backing out of histamine’s role in the process. This diagram shows the cell-by-cell process of acquiring an allergy, but let’s also look at the medical methods used to measure allergy. 

Detailed diagram of allergy acquisition

The incredibly complex process of acquiring an allergy. A) The allergen enters the body. B) An Antigen-presenting cell takes up the allergenic molecule and presents the unique allergens on its surface. The activated antigen presenting cell then migrates to the nearest lymph node. C) T cells recognize the allergen, which differentiate into Th2 cells. D) B cells recognize the allergen through the Th2 cell. E) B cells are activated by allergens. F) B cells differentiate into plasma cells, at which point they would actively synthesize antibodies of IgE from the allergen. G) The IgE antibody that now recognizes the allergen molecule, circulates around the body and attaches to mast and basophil cells. H) When the allergen re-enters the body at a later time it binds to the IgE resulting in a release of chemicals. One of these chemicals is histamine which causes the 5 symptoms of allergic inflammation: heat, pain, swelling, redness and itchiness. Another mediator is IL-4, which affects more B cells to differentiate into plasma cells and produce more IgE and thus the vicious cycle continues. 

The allergic response involves many thousands of interactions, but there are few key markers to look at that can indicate the degree of the reaction, starting with histamine. Please note the team did not test for histamine because the other markers are more effective measures.

  • This substance directly causes allergy symptoms when it’s allowed to interact with our cells, like itchy eyes, runny nose, and reddened skin.
  • Mast cells or eosinophils. Mast cells are part of a class of white blood cells known as eosinophils, and store histamine. All allergies involve these cells releasing stored histamine into the bloodstream. Eosinophilia refers to a condition of elevated eosinophils.
  • IgE or Immunoglobulin E. This is an antibody that recognizes allergy triggers and can be found on the surface of mast cells, telling them to release histamine when an allergy trigger shows up.
  • Airway resistance. One of the most major symptoms of the allergic response is trouble breathing, so an airway resistance test can let an allergist know how much their patient is suffering. It’s a fairly simple test and one of the first you’ll get if you go get treatment for asthma or a respiratory allergy. It involves inhaling a drug called methacholine that constricts the airway. The doctor will continually increase the dose and watch if your breathing becomes more difficult.
  • Inflammation markers. These are a wide group of immune chemicals that mediate the swollen or red tissues portion of an allergic reaction. For this study the team looked for the inflammation marker IL-13, which is also implicated in asthma attacks.
  • Cellular changes. Cells, and in particular immune cells, can change their configuration or undergo what is called metaplasia. This may occur for good or bad reasons, but for the allergic response allergists look for cells that have changed into mucus-producing cells. 

The impact of air purification

Overall it was clear that purifying the air removed the allergy triggers, and their removal improved lung function, markers of allergic reaction in the blood, and the visual presence of mucus-producing cells. Both purifiers were able to remove the airborne allergen in the space compared to a 50% natural settling rate after an hour.

An examination of lung function shows the allergic group suffered greater airway resistance as a result of exposure, and that the HEPA and PECO groups were the same as the normal group.

Graph of airway resistance

When looking at the levels of IgE (allergy-recognizing antibody) and IL-13 (inflammation chemical) in the blood, there was a marked protective effect by filtering the air. 

Graph of plasma IgE and IL-13 levels

The allergic group also had some very clear metaplasia and considerably more mucus-producing cells were observed than with any other group. However, as we will see below, chemical staining of these cells revealed a slightly different story.

Graph of Mucous Cell Metaplasia

Does efficiency really matter?

It is interesting to note that this study was performed before PECO was combined with HEPA in our Tripower filters. A standard HEPA filter has a single-pass capture efficiency much higher than that of the PECO filters used, 99.97% compared to around 95%, yet throughout the study there was nothing HEPA did that PECO didn’t also do. The similar results could be explained by the fact that the purifiers were allowed to continuously clean the air in a small chamber, so while many passes through a HEPA removes almost everything, many passes through another filter will remove pretty close to everything. 

For example, 3 passes through a PECO filter and therefore three 95% removals would have a theoretical efficiency of 99.988%. In the graph below you can see that there were a few hits just above detection level in the PECO chamber after an hour of filtration, though these levels didn’t seem to spur more of an allergic reaction.

Table of Fel d 1 concentration in chambers over time

Fel d 1 aerosol concentration. BDL = Below Detection Level. 

The impact of PECO

There were some unique effects of PECO over HEPA that could be statistically determined to be significant. 

The researchers collected cells from the lungs. The allergic group had a drastically higher number of cells that had shown up as a result of the allergy, followed by the HEPA group, then PECO, then the normal group.

Graph of total BAL cells and eosinophil staining

The cells that were in the lungs of the allergic group tended to be eosinophils, the class of white blood cells that contains histamine-releasing cells. As with the total number of cells, the impact was a little better for the PECO group than the HEPA group.

Number and percent of BAL eosinophils

Careful analysis of lung tissue found that while there appeared to visually be similar amounts of mucus-producing cells in the PECO and HEPA groups, when staining specifically for mucus proteins the PECO group had a better outcome. This was more obvious when the group stained the same area for eosinophils and found the HEPA group was very similar to the full-blown allergy group.

Images of cells stained for MUC5AC, eosinophiles, and DAPI, along with graphs of MUC5AC+ cells and airway eosinophils

How quickly PECO breaks down allergy triggers and other proteins

In addition to the tests above on how they move through the air, the team also sought some information on what happens to allergy triggers that land on the PECO oxidative catalyst and to allergy triggers that don’t. These types of tests can be challenging because they rely on recovering intact proteins from filters, which can’t be done with 100% efficiency.

Cat dander (Fel d 1)

This graph shows how much cat dander was destroyed by PECO compared to HEPA and a PECO filter without the catalyst added after one hour. Less than 8% of the protein segments on the HEPA filter were gone, but 61% were gone on the PECO filter.

Graph of cat dander destruction

Cow and mold proteins

The team also took a look at how PECO can destroy cow albumin (a common test protein) compared to regular removal by carbon or HEPA filters. In these tests the legacy PECO media that has been discontinued as of a few years ago was also compared to the new formulation that is currently being shipped. After 30 minutes, a significant amount of cow albumin could be recovered from the HEPA and carbon filters, a smaller amount from the first version of PECO, and less than 1% from the latest version of PECO. 

Graph of PECO versus HEPA on BSA protein levels

The final test was done with Aspergillus niger, a black mold that causes allergies and other immune issues in some people. The proteins were destroyed relatively easily by both versions of PECO though the latest version was faster, as expected.

Graph of PECO destruction of A niger proteins


These results show that levels of cat dander otherwise undetectable are still enough to trigger allergies. What’s more, the air samples for both the HEPA and PECO groups showed barely any difference in airborne allergy trigger concentration yet differing allergic reactions. Though modern analytical techniques can detect hundredths of a nanogram of cat allergen in the air, it’s not quite enough to gauge the performance of an air purifier on allergy trigger removal.

The researchers speculated that some tiny allergy triggers penetrate filters and can’t be collected with total efficacy. PECO-filters offer two mechanisms for allergy trigger removal, filtration and neutralization, which combined are more effective than filtration alone. This further goes to show that not only is air pollution invisible to our eyes, but not even advanced scientific methods can only measure its effect.

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