Saliva Sneaks Through Efforts to Block Cough

Diseases can spread through coughing despite facial coverings

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) It is generally regarded as common courtesy to cover one's mouth when coughing or sneezing. The reasoning tends to be that covering one's mouth helps prevent germs from spreading. But a recent study has undermined this commonly held belief.

Researchers found that all the techniques recommended to prevent the spread of germs while coughing were ineffective. Microscopic drops of saliva were still able to pass through various barriers.

In this study, although covering one's mouth tended to capture some saliva, it did not prevent small droplets from passing through. This finding suggests that infectious diseases such as the flu and tuberculosis still might be able to spread despite efforts to block a cough.

The researchers urged that further evidence-based techniques used to prevent the spread of disease when coughing need to be studied. According to the researchers, finding which techniques help prevent the spread of diseases when coughing is of primary importance for doctors, intensive care units and the general public.

"Stay home when you have a cough or cold."

Gustavo Zayas, PhD, of the Mucophysiology Laboratory in the Department of Medicine at the University of Alberta in Edmonton, Canada, and colleagues aimed to determine how well mouth covering techniques used to prevent the spread of germs worked.

This study consisted of 31 participants who did not smoke. The participants forced themselves to cough on an open bench while covering their mouths. The researchers used specialized equipment to collect and measure their droplets of saliva.

The participants were instructed to cover their mouths and noses while coughing with either their hands, sleeves, a tissue or by wearing a surgical mask. To measure the saliva, the researchers used a sensory laser beam that was placed 17 centimeters in front of the participants' faces while coughing.

The drops of saliva collected were grouped in six different categories depending on size. The droplet sizes were expressed in micrometers. A micrometer is one-millionth the size of a meter.

The droplets that surpassed the participants sleeves when coughing were about 0.31 micrometers in diameter. Droplets surpassing the tissue, hands and surgical masked when coughing were all about 0.30 micrometers in diameter.

The researchers found that droplets smaller than one micrometer were more abundant than any other droplet size.

The reason that so many droplets were able to pass through these barriers was that they were small and ejected at speeds as high as 100 kilometers per hour.

Even in droplets this small, various diseases are still able to spread. Due to this, the study presents a significant challenge of finding new ways to block the ejection of saliva into the air.

“We all must strive to design highly effective maneuvers and/or devices to block cough droplets of all sizes from dispersing into the surrounding environment, enhancing the control of transmission of infectious respiratory disease and optimizing protection of all members of our society,” Dr. Zayas and colleagues wrote.

This study was published online September 8 in BMC Public Health. The study was funded by the Canadian Institute of Health Research (CIHR) and by the Public Health Agency in Canada (PHAC). The authors displayed no conflicts of interest.

Review Date: 
September 11, 2013
Last Updated:
September 11, 2013