The Effects of Secondhand and Thirdhand Smoke

Medically Reviewed by Neha Pathak, MD on October 13, 2022
4 min read

Being around tobacco smoke is bad for you, even if it's someone else's smoke.

When someone smokes a cigarette, most of the smoke doesn't go into their lungs. It goes into the air, where anyone nearby can breathe it.

Smoking is banned in many public places. But many people are still exposed to secondhand and thirdhand smoke, especially children who live with parents who smoke. Even people who try to be careful about where they light up may not protect those around them.

It can come from a cigarette, cigar, or pipe. Tobacco smoke has more than 4,000 chemical compounds. At least 250 are known to cause disease.

Exposure to secondhand smoke raises the risk -- by as much as 30% -- that others will get lung cancer and many other types of cancer. It can lead to emphysema, and it's bad for your heart. 

Smoke makes your blood stickier, raises your "bad" LDL cholesterol, and damages the lining of your blood vessels. Eventually, these changes can make you more likely to have a heart attack or stroke.

It’s the chemical residue left behind after someone smokes tobacco products or uses electronic smoking devices indoors. The residue builds up over time. It gets stuck in soft surfaces like carpet, furniture, and clothing. It can stay on hard surfaces like walls and floors, including in vehicles. Trying to air out a room or mask the odor doesn’t remove it. And household cleaning doesn’t always remove all the leftover chemicals.

Researchers continue to study how thirdhand smoke affects our health. They've found several chemicals and substances in thirdhand smoke, some of which are carcinogenic. That means they could possibly lead to cancer. 

Nicotine in tobacco reacts with nitric acid (which is naturally in our air) and forms carcinogens. When nicotine stays on surfaces, it continues to react with nitric acid and makes carcinogens. Some research has found it can damage human DNA. Studies in mice show harm to organs and cells. 

Thirdhand smoke raises biomarkers known to cause skin diseases like psoriasis and contact dermatitis. Being around thirdhand smoke also boosts biomarkers linked to oxidative stress, which can damage your cells. This can lead to other diseases like heart disease, cancer, and atherosclerosis (hardening of the arteries).

If you go into a space where someone has smoked, you may be exposed to secondhand and thirdhand smoke.

In addition to small children, poorer people are at risk for exposure to all types of smoke. First, they are more likely to smoke. As a result, their children are exposed to secondhand and thirdhand smoke. 

In one study, researchers looked at levels of cotinine (the chemical that shows up in your urine after you’re exposed to smoke) in children. It was more than five times higher in children whose families lived in poverty compared to those in families with more money. 

People who rent homes or move a lot may be more at risk for thirdhand smoke exposure. One study found that thirdhand smoke builds up and stays in a smoker's home, even if the space is vacant for 2 months and then cleaned. Even if a nonsmoker moves in, they’re exposed to surfaces and dust that contain harmful chemicals from the smoke.


Kids are particularly at risk for the effects of secondhand smoke because their bodies are still growing and they breathe at a faster rate than adults.

These conditions have been linked to secondhand smoke exposure in children:

  • Sudden infant death syndrome (SIDS)
  • More respiratory infections (such as bronchitis and pneumonia)
  • More severe and frequent asthma attacks
  • Ear infections
  • Chronic cough

Smoking during pregnancy is especially dangerous to the developing baby. It's tied to premature delivery, low birth weight, sudden infant death syndrome, limited mental ability, trouble with learning, and ADHD. The more cigarettes a mother-to-be smokes, the greater the danger to their baby.

Secondhand smoke can affect children, even when other household members smoke outside. Babies are especially at risk because they spend a lot of time indoors. They're exposed when they lie, sit, and crawl on floors. They also touch multiple surfaces and then put their hands in their mouths.  A study done on mice shows that exposing babies to thirdhand smoke -- both in the womb, and early on in life -- can affect their immune cells.

It's fairly simple: Avoid being around people who are smoking, and try to convince those around you who smoke to quit. Anyone who does smoke should do so outside, as far away from other people as possible.

Your home is probably the most important place to keep smoke-free, especially if you have children. Keeping kids (and adults) far away from smoke can help lower their chances of having respiratory infections, severe asthma, cancer, and many other serious conditions.

It can be hard to avoid thirdhand smoke completely. If you go indoors, you may be exposed. Even if no one smoked there recently, or smoked in another room on another floor, the harmful chemicals can travel through vents. Some research shows that being around others exposed to thirdhand smoke outside of a space can still expose you to the chemicals. 

To lower your risk of exposure, don't smoke indoors. Remove or replace soft surfaces that can contain chemicals from past smoking. If you own a property, don’t let people smoke indoors. Thoroughly clean surfaces and replace soft surfaces to help lower the amount of chemicals from thirdhand smoke.