I recently wrote about the immediate need for a simple, effective, and readily available defense against COVID-19 and whatever pathogen comes along next. I argued that we need an inexpensive and accessible decontamination method for personal protective equipment (PPE). Such a method will allow for safe reuse of PPE and better protection against COVID-19, especially for health and frontline workers and vulnerable populations.

Now that the World Health Organization (WHO) has released its study on mask decontamination methods—Development of Methods for Mask and N95 Decontamination, or DeMaND—I’m pleased to share the solution to that urgent need.

In partnership with a global consortium of experts, we’ve discovered that the answer is deceptively simple. The world’s biggest challenge in centuries can be solved by nature’s most basic technologies: dye and light.

The DeMaND study concluded that methylene blue (a light-activated dye) and light—MBL in the study—“robustly and consistently inactivated” all three coronaviruses tested, including SARS-CoV-2, the virus responsible for COVID-19. It deemed MBL an effective and low-cost decontamination method for PPE. Those findings hold great potential for overcoming this pandemic, from well-resourced hospitals and medical centers to low-resourced communities around the globe. To review the entirety of the study’s findings, read: Addressing Personal Protective Equipment (PPE) Decontamination: Methylene Blue and Light Inactivates SARS-CoV-2 on N95 Respirators and Masks with Maintenance of Integrity and Fit.

As we continue to fight the devastating effects of the COVID-19 pandemic, light-activated dyes such as methylene blue are ideally suited for decontaminating PPE. Here’s why.

What about PDT?

This spring I got an email from Carolyn Chen, a radiology resident at Virginia Mason Medical Center here in Seattle. Carolyn worked with me on my last enterprise: developing a crowd-sourced method for objectively rating surgeon performance, an assessment that was ultimately acquired by Johnson & Johnson.

She wanted to put me in touch with her father, Dr. James Chen, a respected neurosurgeon and oncology researcher who focused on using photodynamic dyes to break up cancer cells. Her dad had an idea, she said. Could I talk to him?

Like me, Dr. Chen was concerned with the global shortages in PPE and the negative impact that widespread PPE reuse had on health workers.

What about PDT (photodynamic therapy)?, he asked me in our first phone call. Could the pathogen-fighting principles of PDT and light-activated dyes be used to help with PPE shortages?

He was onto something. We got in touch with a contact at the CDC who was preparing a presentation for WHO’s upcoming COVID-19 taskforce meeting. They added our proposed decontamination method to the agenda.

After that initial meeting, the taskforce was interested. They recommended that a few members study the hypothesis, and we were off to the races.

The pathogen-fighting powers of light-activated dyes

Dr. Chen has spent much of his career in the field of PDT, studying how light-activated, or photodynamic, dyes can treat cancers. (Here Dr. Chen explains what PDT is and how it works.) He theorized that the basic principles of light-activated dyes could be applied to decontaminate masks and other PPE.  

Together, we tested that theory. We developed a basic solution of methylene blue (a light-activated dye that’s readily available) in water to spray onto PPE to decontaminate them from COVID-19 and other pathogens.

Without getting too technical, here’s how the science works:

When hit by light, certain dyes, such as methylene blue, react with oxygen in the air to create singlet oxygen. COVID-19 and other pathogens are no match for oxygen in this highly energized state. Singlet oxygen destroys pathogens like viruses, bacteria, and fungi on contact. That’s why methylene blue dye has been used as a sterilization method for human plasma transfusion.

If our theory proved true, light-activated dyes could be used as an effective, low-cost  alternative to the two prevailing decontamination methods for PPE, vaporized hydrogen peroxide, or VHP, and UV light, both of which require considerable resources.

Research methods

We created a consortium of labs to develop the research design and test the hypothesis. I say this with humility: You could not put together a better team. The group includes the world’s top minds in photodynamic therapy and virology. The labs themselves combine deep expertise and specialized research and testing equipment.

The consortium tested two decontamination methods to determine their efficacy as effective, low-cost alternatives to VHP and UV light:

  1. A solution of methylene blue in water combined with light, or MBL
  2. Dry heat (DH in the WHO study)  

For each decontamination method, we tested:

  1. Its effect on a range of masks and materials: three N95 respirators, two medical masks, and one cloth community mask (representing the bulk of masks used globally)
  2. Its effectiveness in deactivating COVID-19 particles (SARS-CoV-2), along with Murine Hepatitis Virus (MHV) and Porcine Respiratory Coronavirus (PRCV)
  3. How each type of mask held up after five decontamination cycles across six integrity-testing sites

WHO’s DeMaND study

Our hypothesis proved true. Singlet oxygen—the byproduct of light-activated dyes such as methylene blue—was effective at killing the viruses tested, most notably SARS-CoV-2, the virus responsible for COVID-19.

The results of our testing were detailed in the recently released Addressing Personal Protective Equipment (PPE) Decontamination: Methylene Blue and Light Inactivates SARS-CoV-2 on N95 Respirators and Masks with Maintenance of Integrity and Fit. As I mentioned above, the study concluded that methylene blue (the light-activated dye) and light, or MBL, “robustly and consistently inactivated” COVID-19.

“We provide the first evidence that methylene blue and light can inactivate human coronavirus on [filtering facepiece respirators] and [medical masks] commonly worn by healthcare personnel and essential workers without decreasing performance and fit. Our findings provide a recipe for easily accessible, inexpensive, effective PPE re-use and afford an opportunity for utilization in high- and low-resourced settings to address issues of global supply shortages and reduced time of decontamination relative to [vaporized hydrogen peroxide plus ozone decontamination method].” -WHO DeMaND study

Here’s what the study found:

  • Methylene blue and light, or MBL, consistently deactivated virus particles across all mask types tested.
  • Medical and respirator mask integrity held up after five cycles of decontamination with methylene blue. Cloth mask results varied, but with only minimal reduction in performance.
  • Not only did MBL inactivate virus particles, it was incredibly effective at doing so. We tested methylene blue with 50,000 lux (equivalent to the kind of simple white light available at a hardware store or about a third of the intensity of light on a sunny day) for 30 minutes. Yet, after only five minutes of light exposure, the virus particles were already completely deactivated. Even a very low concentration of methylene blue paired with low light was successful at inactivating SARS-CoV-2 particles. Its effectiveness at killing the virus particles was “strongly enhanced” by a powerful light source.

What’s next for safe, effective, and low-resource PPE decontamination methods

The study concludes that “MBL decontamination of masks is effective, low-cost, and does not require specialized equipment.” It demonstrated “complete decontamination of masks” treated with viral loads equivalent to those secreted by hospitalized patients, while maintaining mask integrity. Perhaps most importantly, it validated a decontamination method that can benefit a range of settings, from well-funded medical centers to low-resource communities.

The results are especially promising for remote and underserved parts of the world. Unlike vaporized hydrogen peroxide and UV light decontamination methods, MBL is inexpensive, accessible, safe, effective, and simple. As the WHO study notes, it “could be introduced globally with simple, non-electricity dependent methods.”

We will continue testing to discern the most efficient and effective combination of light-activated dye concentration, light strength, and length of exposure. We aim to perfect the recipe to provide the biggest impact.

Methylene blue and light can effectively inactivate human coronavirus on PPE. This simple technology has the potential to save tens of thousands, if not millions, of lives. It can give health and frontline workers the protection they deserve. While we wait for vaccines to be broadly distributed—and even after they’re widely available—light-activated dyes such as methylene blue can help us stay safe and save lives, during a pandemic and beyond.

Development of Methods for Mask and N95 Decontamination (DeMaND) study

Review the entirety of the DeMaND study’s findings: Addressing Personal Protective Equipment (PPE) Decontamination: Methylene Blue and Light Inactivates SARS-CoV-2 on N95 Respirators and Masks with Maintenance of Integrity and Fit.

About the author

Thomas Lendvay, MD

Singletto Chief Medical Officer

Thomas Lendvay is a physician, surgeon, and entrepreneur. He is Attending Pediatric Urologist and Program Director for the Pediatric Urology Fellowship at Seattle Children’s Hospital, where he co-directs the robotics program. He’s also a professor in the Urology department at the University of Washington. Dr. Lendvay invented a surgical assessment that was acquired by Johnson & Johnson, which earned him the UW Medical School Inventor of the Year Award in 2018.

Dr. Lendvay is an originator of and leading contributor to the World Health Organization DeMaND study on the use of methylene blue dye as a safe, low-cost decontamination method to allow for safe reuse of PPE and better protection against COVID-19, especially for health and frontline workers and vulnerable populations.

View Dr. Lendvay’s full bio.

Read Dr. Lendvay’s earlier article on why we need simple, effective ways to decontaminate potentially COVID-infected PPE—now.


November 15, 2021
Protective Dye Methylene Blue Plus Light Proven to Inactivate "Hard-to-kill" Norovirus

Singletto's Dr. Lendvay contributed to a New MB Study


May 22, 2021
Infection Control & Hospital Epidemiology Publishes Drs. Lendvay, Chen, et al. WHO-led DeMaND Study

The Infection Control & Hospital Epidemiology medical journal has published the peer-reviewed DeMaND study. Singletto’s Dr. Tom Lendvay served as Lead Author.


May 20, 2021
Top Doctor 2021: Singletto’s Lendvay Named by Seattle Magazine

Dr. Thomas Lendvay, Singletto’s Co-Founder and Chief Medical Officer was just named a “Top Doctor” by Seattle Magazine.


March 25, 2021
A Moral Obligation: Why the Former Providence President Wants Singletto Tech Out Now

Mike Butler spent over two decades in leadership at Providence Health, growing such from a $2 billion organization to $25 billion. Upon recently retiring, Mike knew he wanted to find ways to continue impacting the lives and health of others. Now at Singletto, Mike is on a mission to bring the novel Singletto technology to market – in healthcare and beyond. But, it’s not just a passion project … upon learning about the technology, Mike felt a moral obligation to get it in as many hands as possible. More with recently retired Providence Health President Mike Butler…


February 25, 2021
Hospital News: Light kills. SARS-CoV-2, That Is.

Singletto Advisor Dr. Belinda Heyne shares DeMaND study results on Hospital News.

Lacey Duffy

Customer Experience
February 12, 2021
CBC: This simple mix of dye and light could decontaminate masks for reuse

Dr. Belinda Heyne was recently featured in a CBC piece covering the DeMaND study’s findings and the life-giving potential of dye and light.