<unk> s from humans include various cells types (e.g. epithelial cells and cells of the immune system), physiological electrolytes contained in mucous and saliva (e.g. Na+, K+, Cl−), and, potentially, various pathogens.<unk> s that dry in the air become<unk>  nuclei which float as aerosols and can remain suspended in air for considerable periods of time. The probability density function for<unk> s in the breath of someone speaking, as a function of diameter. Note that both axes are log scales, we breathe out<unk> s ranging in size from less than a micrometre to around a millimetre, and that we breathe out many more<unk> s around a micrometre across than larger<unk> s. Only the largest<unk> s, around a millimetre in size are visible, we cannot see the smaller ones. The traditional hard size cutoff of 5 μm between airborne and<unk> s has been criticized as a false dichotomy not grounded in science, as exhaled particles form a continuum of sizes whose fates depend on environmental conditions in addition to their initial sizes. However, it has informed hospital based transmission based precautions for decades.
Respiratory droplet
Dental aerosol
Airborne 
Inhalation
Dental instrument
Ventilated cigarette
Cigarette
Snuff 