What is a known harmful effect of secondhand smoke?

Secondhand smoke is recognized as a harmful toxin due to its composition, which includes thousands of chemicals, many of which are known carcinogens. Exposure to secondhand smoke can lead to various health issues, particularly in vulnerable populations such as children and individuals with preexisting health conditions. The health risks associated with secondhand smoke include respiratory infections, asthma attacks, and a heightened risk of cardiovascular diseases. The detrimental effects extend to both the immediate respiratory irritation and long-term chronic disease implications for those involuntarily exposed.

By understanding that secondhand smoke is indeed a harmful toxin, it's clear why this answer is the most accurate choice in identifying a significant risk associated with exposure.