Nanoparticles are tiny particles that are about one-millionth the size of a human hair. They can be found in the air we breathe, the water we drink, and the soil we eat. Some nanoparticles are naturally occurring, while others are man-made.

Man-made nanoparticles are used in a variety of products, including cosmetics, sunscreens, and food additives. They are also used in industrial processes, such as welding and metalworking.

Nanoparticles can enter the body through the lungs, the skin, or the gastrointestinal tract. Once inside the body, they can travel to different organs and tissues.

The health effects of nanoparticles are still being studied. Some studies have shown that nanoparticles can cause inflammation and damage to cells. Other studies have shown that nanoparticles can cross the blood-brain barrier and enter the brain.

Air pollution is a major source of nanoparticles. Many different air pollutants, such as diesel exhaust, cigarette smoke, and industrial emissions, contain nanoparticles.

Exposure to air pollution can increase the risk of a variety of health problems, including:

* Lung cancer

* Heart disease

* Stroke

* Asthma

* Bronchitis

* Pneumonia

* Diabetes

* Obesity

* Birth defects

* Low birth weight