California has enacted the world's first law targeting "thirdhand smoke," the persistent chemical residue left on surfaces after smoking. Unlike secondhand smoke, which dissipates, thirdhand smoke embeds in materials and can react with indoor pollutants to form cancer-causing compounds. Experts warn it poses a unique danger, particularly to infants and toddlers, due to absorption through skin, inhalation, or ingestion. This law signifies a significant advancement in public health awareness regarding tobacco's lingering effects.