How Effective Are Surgical Face Masks

Dr. Rich Davis, PhD, D(ABMM), MLS is Clinical Microbiology Lab Director at Sacred Heart Medical Center, Spokane, WA. He did two simple demonstrations to show the effectiveness of a properly worn surgical face mask in reducing the spread of biological contaminants. The first demonstrates the effectiveness of a mask to block respiratory droplets at a fixed short distance under different circumstances. The second demonstrates the effectiveness to block respiratory droplets at varying distances if the wearer is coughing.

In all of the demonstrations, standard agar culture plates are used to show the level of contamination from respiratory droplets. After a few days, the culture plates show the presence (or absence) of bacteria (not viruses) and are meant to be a proxy for biological contaminants in the droplets.

In the first demonstration, Dr. Davis held a culture plate about a foot in front of his face for each test: while sneezing, singing, talking, and coughing -- each without and with a mask. The setup is shown below.

Here are the results:

In the second demonstration, Dr. Davis stood with a table in front of him. Three culture plates were placed on the table at distances of 2 feet, 4 feet, and 6 feet. He then coughed hard for approximately 15 seconds with no mask. This was repeated while wearing a mask. The setup is shown below.

Here are the results:

According to Dr. Davis, a properly worn mask blocks respiratory droplets from your mouth and throat. Wear a mask when in public. It's the responsible thing to do.

John L. Ferri

jlferri@epix.net