With numerous mechanisms to trap potentially harmful particles, our bodies are adept at protecting us from certain hazardous contaminants. As the size of the contaminant decreases however, so too does the body's ability to defend itself against them. Typically, particles smaller than five microns pass the body's defence mechanisms and enter the lungs or bloodstream.
This is where the importance of air filters comes to the fore. By removing the smaller, most harmful particles from the air around the body, filters offer the defence that the body can't provide.
In spite of this, just because the body can protect us from particles greater than five microns, does not necessarily mean they should. In some cases, such particles can pose a risk to both short and long-term health and, if filters are employed to remove these larger particles, our bodies are free to get on with more critical areas of protection.