'Thirdhand smoke': Lesser-known cigarette threat as world-first law goes into effect in Cal.

 Starting today, California is taking a stand against thirdhand smoke.

While most people are well aware of the health threat of secondhand smoke — what you inhale from someone smoking a cigarette nearby — “thirdhand smoke” is much less discussed. But it may actually be more toxic.

It can certainly have a very real effect on your health, upping your chances of cancer and heart disease — and the Golden State has just enacted the first law in the world to combat it.

Thirdhand smoke is the chemicals from smoke that sticks to surfaces long after the smoking stops — and can then renter the air. A new California law requires homeowners to disclose thirdhand smoke when selling property.Degimages – stock.adobe.com

Introduced by Assemblymember Catherine Stefani (D-San Francisco) and passed unanimously, California Assembly Bill 455 requires homeowners to disclose any history of thirdhand smoke or vaping residue when selling their property.

If the seller has knowledge of any past smoking or nicotine use in the home, they must tell potential buyers in writing.

The state’s Homeowners’ Guide to Environmental Hazards is also being updated to include thirdhand smoke.

That’s because thirdhand smoke lingers in the places people have smoked, even when they are no longer smoking or in the room. The chemical residue gets into fabrics, sticks to surfaces and even clings to the walls.

It can stay there for months and even years, impacting those in the environment who may breathe it in, ingest it via dust, or touch it.

“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,” explained Neal Benowitz, MD, a UC San Francisco professor emeritus of medicine and co-author of a recent paper on thirdhand smoke.

The threat of thirdhand smoke exposure is similar to that of secondhand smoke exposure, an increased risk of cancer chief among them. It also puts people at risk for heart disease, lung illness and birth defects.

“In mice, researchers have found that thirdhand smoke exposure causes DNA damage, can cause or promote cancer, cause immune dysfunction and behavior disturbances,” Benowitz told Medical Xpress. “Studies of people exposed to thirdhand smoke found changes in blood proteins that have been associated with inflammation and heart disease.”

Babies are most at risk because they crawl on the floor.New Africa – stock.adobe.com
He warned that the most at-risk populations include people with allergies and asthma, as well as children, “who crawl on the floor, can put objects contaminated with thirdhand smoke into their mouths, and can absorb it through the skin.”

Those who live in multi-unit low-cost housing are also more likely to be exposed. Benowitz said he hopes future legislation will tackle this problem to help renters.

“In many cases, a smoker moves out of an apartment and a nonsmoker moves in unaware of the risk,” he said.

While the threats are similar, thirdhand smoke behaves a bit differently from secondhand smoke — and may be more toxic.

'According to new research from the Chinese Academy of Sciences, secondhand smoke disperses quickly. Thirdhand smoke, however stays in the air longer, albeit at a low level. It also becomes more nitrogen-rich over time, which may make it more harmful.'

“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.

“A smoking session may end, but the release of hazardous compounds persists, exposing people to low levels of toxins long afterward. This turns our homes into environments of chronic, low-dose exposure.”

https://nypost.com/2026/01/01/health/what-is-thirdhand-smoke-cigarette-health-threat-as-california-law-goes-into-effect/