A Quick Note About UV Light for Sterilization

Posted: March 30, 2020 in Uncategorized

With the onset and spread of SARS-CoV-2 virus and the COVID19 it causes, I have seen many offer up the idea of using low cost UV light sources used primarily for curing resins and/or finger nail polish, as a method for sterilizing surfaces and used masks. Cutting to the chase… a $35 nail salon cure light is not going to work.

These sources use light between 365nm and 405nm, depending on the intended application. This is considered long wavelength UV light, or UVA (315 to 400nm). While these may be somewhat effective against some bacterial invasions, with extremely long exposures and/or very high intensity levels (well beyond those of a small cure light), there is no evidence this is a reliable sterilization solution for viruses.

To kill viruses, hospitals are now using UVlight robots that emit high levels of UVC radiation between 200nm and 280nm, and the primary germicidal range for UVC is between 254nm and 260nm, for periods of around 20 to 30 minutes – on top of chemical cleaning and sterilization procedures. The reason they use robots, is that this radiation is dangerous to human occupants, so is not done when anyone is in the room. UVC disrupts the DNA and RNA of micro-organisms, which prevents them from reproducing. Read Here for more on these machines and their use.

Note that while UVC radiation is being applied in the fight against viral contamination on surfaces, it is not used alone. Chemical disinfection is often used in concert with UVC light, as this does more than disrupt DNA/RNA, it kills the micro-organisms, and wipes them away.

While there is evidence that narrow spectrum UVC light, between 207nm and 222nm, which cannot penetrate skin, is as effective as any other UVC source, finding such sources is somewhat difficult, and the risk of failure (from dangerous UVC light exposure) enough of a concern, that this may not be a practical solution – yet.

Light in the 365nm to 400nm range used on cheap cure lights is not going to destroy a virus, or disrupt its DNA, or remove it. These are not going to do anything but provide a false sense of security that will potentially lead to exposure to the very infection one is attempting to protect oneself from.

Another issue with short wavelength UVC light, is its limited capacity to penetrate materials or reach beyond surfaces, particularly those used in surgical and N95 masks. For a $25 toothbrush sanitizer or $50 cell phone sterilizer, this is not a serious issue. With an exposure of between 6 and 10 minutes, UVC has been shown to reduce the presence of harmful micro-organisms on surfaces in these applications. However, using a cell phone sanitizer to sterilize a fabric mask has not been proven, nor is it recommended. If the light cannot penetrate the mask’s many layers and fibers, and underlying filter materials which trap organisms (their purpose), it is unlikely that any real effect will be realized.

For more on this topic,’Disrupting the Transmission of Influenza A: Face Masks and Ultraviolet Light as Control Measures‘ reveals that the combination of UVC light for disinfecting surfaces and equipment, combined with face masks, is effective in fighting Influenza A. However, this does not necessarily apply to SARS-CoV-2 or COVID19, nor was it suggested that UVC was a viable strategy for sterilizing face masks.

There are no recommendations for disinfecting face masks using UV light to protect a user from being infected. In fact, the FDA states that surgical masks and N95 masks are not recommended for public use to protect from infection. Broad miss-use does not change this reality. While trained hospital staff may be able to rely on the N95 mask for some exposures, frequently used in conjunction with face shields, applied expertly, to protect themselves from infection. The general public has none of these qualifications.

If the masks are improperly cared for, or treated to ineffective disinfection processes, the result may be more harmful than having nothing at all. Think about this: The purpose of the mask is to capture micro-organisms and hold them on the surface and within the filter media. If that is contacted during mask removal, and the hand or finger touches an eye, or a lip, the virus has been given the free ride it was looking for – those warm and moist mucus membranes. Wave that soiled mask around a little as you remove and store it, and a few of those micro-organisms escape, and fly, then fall on surfaces around you. Now, handle that mask even more to insert it into a make-shift UV light box, and the exposure sequence continues. Take that same soiled mask, after inadequate treatment (still filled with bugs), and put it back on… get the picture? For the general public, the mask may act more like a bug collection devise for dispersion at home – than an actual protective device.

That said, there is one process that has been FDA approved for limited use (state of Ohio at this moment), which uses Vapor Phase Hydrogen Peroxide by Battelle CCDS to sterilize used N95 masks without reducing filter efficiency. This cannot be done at home.

The only known strategy for protecting oneself from being infected, is distancing oneself from others, either through isolation or active distancing, plus careful and diligent hygiene (hand washing, avoiding contacting surfaces of unknown exposure, and avoiding touching the face, particularly eyes, nose and mouth.

I offer this only to help those who might believe themselves safer through home baked solutions that actually produce higher risk of infection. Please, be safe, and be well.


In addition to the exploration above, I found this at the SAGES (SOCIETY OF AMERICAN GASTROINTESTINAL AND ENDOSCOPIC SURGEONS) . This is an article on the topic of re-using N95 masks, that specifically states that use of UV light renders them unusable. Further, it states that all contact with metal must be avoided. It specifically states:

When sterilizing N95 masks, be wary of using UV light–keep N95 masks away from UV light / sunlight. N95 masks are degraded by UV light because it damages the electrostatic charges in the polypropylene material. It is unclear how long the masks can be exposed to UV light before they are ineffective.

It re-iterates this again:

Keep N95 masks away from UV light / sunlight.

That appears to indicate that use of UV light for disinfecting N95 masks with UV Light.

The Delaware Health and Social Services has issued guidlines for use of surgical masks, which is also worth looking at, for those concerned. They state:

• Using surgical masks will not fully protect you from being infected. Hand-washing, isolating infected
patients, and covering the mouth and nose when coughing also help to reduce to the risk of infection.
• Masks must be changed when they become wet with saliva or other bodily fluids, as they lose their
protective properties.
• Surgical masks are not tested against specific microorganisms and do not prevent specific diseases.
• Never reuse, wash or disinfect surgical masks.
• Never share surgical masks with others.
• Place used or soiled masks into a tied plastic bag to prevent dripping.
• Wash hands thoroughly with soap and running water, or use an alcohol-based hand gel after handling.

Please, be safe, and stay well, and most of all, stay informed. Small mistakes can be very costly when you are dealing with infectious micro-organisms.

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