Although AGM/DP have been implicated in spread of viral contagion, it must be remembered that aerosols are generated during normal physiological activities such as breathing, talking, coughing, and sneezing. Studies on healthy volunteers have demonstrated that mouth breathing produces 1‐98 particles per liter, with a median diameter of 0.3 μm; with only about 2% of the particles  >1μm and none > 5 μm. During speaking, 1 to 50 particles in the 1 μm range are emitted per second (0.06 to 3 particles per liter); with some ''super‐seeders'' expelling as many at 200 particles per second while speaking loudly. Singing creates six times as many droplet nuclei as talking and is equivalent to coughing. Sneezing can expel nearly 40,000 droplets between 0.5 to 12 μm at speeds of almost 100 m/sec, while coughing may generate up to 3000 droplet nuclei. Collectively, studies such as these demonstrate that healthy individuals generate particles sized between 0.01 and 500 μm, underlining the fact that dispersal of expelled particles does not occur exclusively by airborne or droplet transmission but by both mechanisms concurrently.

Although healthy and diseased individuals generate aerosols during normal activities, evidence that these aerosols contain an infectious agent is equivocal. For example, Streptococcus pneumoniae, Staphylococcus aureus, Methicillin‐resistant Staphylococcus aureus (MRSA), Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia, Haemophilus influenzae, Legionella pneumophila, Mycoplasma pneumonia, Chlamydia pneumonia, and Mycobacterium tuberculosis can be detected in 36% of patients with symptomatic respiratory diseases. However, although 89% of nasal swabs were positive for live virus in 142 patients diagnosed with influenza A, only 39% of individuals exhaled live viral particles in their breath, and the number of particles shed declined significantly within 3 days of onset of symptoms. Importantly, these particles failed to land on targets placed at a distance of 0.1 and 0.5 m. Furthermore, when a patient wore a surgical mask, it reduced the viral shedding in aerosol by 3.4 fold. On the other hand, P. aeruginosa can travel 4 m and persist in the aerosol for 45 minutes subsequent to a coughing episode. Wearing surgical masks for 10 to 40 minutes reduced the levels of respiratory pathogens by more than four‐fold.

Collectively, there is a large body of evidence that patients in the acute phase of respiratory infections are capable of disseminating large numbers of airborne microorganisms during activities such as breathing, talking, singing, coughing, and sneezing. This shedding can be mitigated by the simple act of wearing a mask and is effective against viral as well as bacterial pathogens.