A major health concern of smoke comes from particulate matter, solid particles and liquid droplets found in air. In smoke, these particles often are very tiny, smaller than 2.5 microns in diameter. How small is this? For comparison, the diameter of the average human hair is about 30 times greater. These particles can build up in your respiratory system, causing a number of health problems including burning eyes, runny noses and illnesses such as bronchitis. The particles also can aggravate heart and lung diseases such as congestive heart failure, chronic obstructive pulmonary disease, emphysema and asthma.