Newborns exposed to chemicals used to produce nonstick cookware, firefighting foam, paper products and other items weigh slightly less and have slightly smaller skulls, according to preliminary research conducted at Johns Hopkins University.

Dr. Lynn Goldman, a pediatrician and professor at the university’s Bloomberg School of Public Health, said the study of 300 babies found “very small decreases” in birth weight and head circumference. The babies were born at John Hopkins Hospital in Baltimore between 2004 and early 2005. The mothers ranged in age from 14 to 43.