Researchers from São Paulo’s School of Medical Sciences of Santa Casa have found that second-hand smoke negatively affects a child’s hearing. The researchers tested 145 students between ages 8 and 10 that showed normal hearing in standardized tests. Their secondhand smoke exposure was measured by the level of a nicotine metabolite in the children’s urine. The 60 youngsters that had been exposed to secondhand smoke showed significantly lower responses to certain frequencies in both ears when compared to the others that weren’t exposed to the smoke.

Researchers suspect that the affecting mechanism may be the acrolein gas that forms from burning tobacco cigarettes. The chemical was found to damage ear cells in a study published in the International Journal of Pediatrical Otorhinolaryngology. A 2012 study of diesel exhaust, which likewise produces acrolein gas, by the Republic of Korea’s Dongguk University, also showed damage to middle ear cells.

Supporting these results, a study published in the American Medical Association Otolaryngology and Head and Neck Surgery Journal found that smoking during pregnancy almost triples the risk of low-frequency hearing loss in the child. The study tested 964 adolescents between ages 12 and 15, of whom 16 percent were exposed to prenatal smoking.