Expose your children to secondhand smoke, and lead levels in their blood will spike, according to researchers at the Hopkins Bloomberg School of Public Health. Since even small amounts of lead can poison a child (or adult, for that matter), this news is especially alarming. Consider this: one in five U.S. children live with someone who smokes.

Lead is an ingredient in tobacco smoke, measured in both the smoke exhaled by the smoker and in the smoke from the burning cigarette. According to the Centers for Disease Control, a speck of lead dust, as small as a grain of sand, can poison a child, and at low levels, is highly toxic for neurocognitive development and kidney function.

The new study, published in a recent edition of the American Journal of Public Health, evaluated secondhand smoke and its relationship with children between the ages of 3 and 19, all participants in the National Health and Nutrition Examination Survey (NHANES), conducted between 1999 and 2004. The 6,830 children were chosen because they were not active smokers and their blood level measurements were available.

The study found that living with one or more smokers significantly increased the children’s lead levels, greater in younger children, which researchers said might be attributed to the greater amount of time younger children spend at home or with a relative who smokes. Existing childhood lead poisoning prevention programs evaluate children’s blood lead levels by considering housing, lead paint hazards, sources of drinking water and industrial plants near homes. Lead from secondhand smoke usually does not come into play. The Hopkins researchers suggest that lead prevention programs should also evaluate smoking exposure at home, and smoke-free environments should be provided for children to reduce lead exposure.

For more about lead and its dangers, click here.