A new study found that microscopic nanoparticles from laser printer toner could cause changes in the human body that would make catching diseases much more likely.

The study was spearheaded by West Virginia University School of Public Health researcher Nancy Lan Guo.

Guo’s team studied rats living in a chamber as a laser printer ran nonstop, five hours a day for 21 days.

The researchers found that a single day of toner-particle exposure was enough to change how genes associated with metabolism, immune response and other biological process worked.

“I don’t want to alarm people, but special ventilation and exposure controls should be installed in rooms where laser printers are in heavy-duty use, because the concentration of nanoparticles released in the air during the printing and copying process is strongly correlated with the printing activities,” Guo told Science Daily.

Guo said she and her colleagues are now investigating how the toner has affected the genome of Singaporean printing company workers.