Children who are exposed to even extremely low levels of tobacco smoke in the last 5 days score lower on standardized tests. Their performance on math tests is significantly lower, but lower still on reading tests. Their short-term memory scores appear to be unaffected. These startling results come from an analysis of 4,399 children 6 to 16 years old published in the January 2005 Environmental Health Perspectives (the NIH journal on environmental health).
Exposure to smoke was strongly associated with decreased cognitive ability. This held true even after adjusting for gender, race, region, poverty, parent education, parent marital status, and blood tests for iron and lead. The level of tobacco smoke exposure was measured by blood tests as well as by asking questions. The greater the exposure, the poorer the children performed on intelligence tests, but the biggest drops in scores happened at the lowest levels of exposure. There is no safe level of smoke exposure for their developing brains. Any tobacco smoke that children can smell appears to be enough to affect their intelligence.