Every day, we inhale and exhale without a second thought. Why? Because we believe we breathe fresh air. The fresh air we hope to breathe consists of a mixture of simple gases, mainly oxygen and nitrogen. However, this air can be polluted with very different tiny particles emitted from natural sources and human (anthropogenic) activities in our day-to-day life, which might be harmful to our health. These tiny particles are known as nanoparticles. This blog post explains how nanoparticles are released in our environment, their sources, how they end up in the air we breathe, the nanoparticle cocktail in urban and rural areas, and their potentially harmful effects on humans and the environment.