California has enacted a first-of-its-kind law aimed at reducing exposure to thirdhand smoke, the toxic residue that lingers in homes long after smoking ends.
The new California law took effect on Jan. 1.
Thirdhand smoke refers to chemicals from tobacco smoke that settle into walls, floors, furniture, fabrics and dust, where they can persist for months or even years.
Unlike secondhand smoke, which is inhaled while someone is actively smoking nearby, thirdhand smoke can reenter the air over time or be absorbed through skin contact or ingestion.
Health researchers warn that this residue can increase the risk of cancer, heart disease, lung illness and birth defects, particularly for children and people with asthma or allergies.
Children face a higher risk because they spend time on floors, touch contaminated surfaces and put objects into their mouths.
The New York Post reported that California Assembly Bill 455, introduced by Assemblymember Catherine Stefani, requires homeowners to disclose any known history of smoking or vaping residue when selling a property.
If sellers are aware of past nicotine use in the home, they must notify potential buyers in writing.
The state's Homeowners Guide to Environmental Hazards will also be updated to include information on thirdhand smoke exposure.
Medical researchers say thirdhand smoke is more than an unpleasant odor and serves as an indicator of chemical contamination.
"Thirdhand smoke is not just an irritating smell in the home. It indicates that the home is contaminated with potentially harmful chemicals derived from tobacco smoke," said Neal Benowitz, MD, a University of California, San Francisco professor emeritus.
Benowitz said studies show exposure can cause DNA damage, immune dysfunction, inflammation, and changes linked to heart disease.
Research has also found that thirdhand smoke behaves differently from secondhand smoke by remaining in indoor air at low levels for extended periods.
A study by the Chinese Academy of Sciences found that thirdhand smoke becomes more nitrogen-rich over time, a change that may increase toxicity.
"The key takeaway is that thirdhand smoke is not a static stain; it is an active, ongoing source of pollution in a room," said Prof. Sun Yele, the study's corresponding author.
Public health experts say the new disclosure law is intended to give buyers clearer information and reduce unknowingly prolonged exposure in residential settings.
Jim Mishler ✉
Jim Mishler, a seasoned reporter, anchor and news director, has decades of experience covering crime, politics and environmental issues.
© 2026 Newsmax. All rights reserved.