What size particles can enter deeply into the lungs?

Particles less than 5 microns are capable of penetrating deep into the lungs. This is primarily due to their small size, which allows them to travel through the respiratory tract and evade the body's natural defenses, such as cilia and mucus that are designed to trap larger particles. Particles that are less than 2.5 microns are particularly concerning because they can reach the alveoli, where gas exchange occurs, and have been linked to various health issues.

The distinction in size is crucial in understanding how particles behave in the airways and what health implications they may pose. Particles in the 2-4 micron range can stand a chance of being trapped in the upper airways, while those larger than 5 microns are more likely to be filtered out before reaching the lower respiratory tract. Therefore, it’s the smaller particles—especially those under 5 microns—that are most concerning regarding deep lung entry and potential health risks.