Secondhand smoke has been known to cause allergies and infections in children, but now scientists say secondhand smoke lowers kids’ math and reading scores as well. In a study published in the journal Environmental Health Perspectives, researchers gave reading, math and reasoning tests to more than 4,000 kids ages 6 to 16. The researchers then measured their blood for cotinine, a substance that’s a marker for tobacco-smoke exposure. The higher the cotinine levels, the lower the test scores. Even trace amounts of cotinine were associated with lower scores. Researchers suggest that smoke may change the nervous system’s structure, which deprives kids of oxygen, thus affecting brain function.