Researchers were concerned about whether inhaled carbon nanotubes could lead to certain lung diseases, including pleural fibrosis, which results in the hardening and thickening of the tissue which covers the lungs, impairing breathing. Testing this hypothesis, they exposed laboratory mice to varied doses of pollutants and nanoparticles. Mice exposed to certain doses of carbon nanotubes developed subplural fibrosis just two to six weeks after inhaling carbon nanotubes. The work suggests that minimizing inhalation of nanotubes is prudent until further long-term assessments are conducted