Medical Discovery News
By Norbert Herzog and David Niesel 

Science has long proved that smoking is bad for you and those around you, with 90 percent of lung cancer cases caused by smoking.

Even secondhand smoke is dangerous enough to warrant banning smoking in public places. The idea of thirdhand smoke premiered in 2009, and scientific evidence shows that it, too, can harm human health.

Thirdhand smoke is the many toxic compounds from tobacco smoke that settle onto surfaces (particularly fabrics) such as carpet, furniture and the inside of a car. Researchers have identified chemicals in thirdhand cigarette smoke called NNA and NNK that can bind to DNA, a person’s genetic information, and cause damage and mutations that could lead to cancer.

There are 4,000 known pollutants in cigarette smoke, including a large number that cause DNA damage. Many of them have been found in the carpets, walls, furniture, dust, clothing, hair and skin of smokers long after they’ve smoked a cigarette. The pollutants from smoke can accumulate over time, making the environment increasingly toxic.

Mainstream smoke has more than 60 known carcinogens, which cause cancer, and other toxins, many of which are present in secondhand and thirdhand smoke. Nonsmokers are exposed to these toxic compounds when they inhale, touch or ingest them off surfaces containing thirdhand smoke.

To make matters worse, some of the smoke residue can undergo a chemical transformation into secondary compounds when it interacts with other indoor pollutants like ozone and nitrous acid. For example, nicotine reacts with ozone in the atmosphere to produce byproducts and ultrafine particles that can trigger asthma attacks.

Other secondary products such as NNA and a related compound called NNK are also formed. A recent study aimed to discover what level of thirdhand smoke mutagens and carcinogens a nonsmoker might be exposed to in realistic scenarios, and whether these levels would be high enough to cause damage to DNA or other adverse effects.

Unrepaired DNA damage can lead to mutations and increase the risk of developing cancer. They concluded that human cells exposed to thirdhand smoke or secondary compounds had increased DNA damage within 24 hours.

These results provide evidence that thirdhand smoke does include carcinogens from cigarette smoke and the environment. The study also showed that NNA and NNK have damaging effects on developing lungs, making them particularly harmful to infants.

Smokers themselves are giving off thirdhand smoke toxins, so going outside to smoke helps but is no solution. It is unclear how long toxic thirdhand smoke compounds continue to be a risk.

Depending on the compound, they may linger for hours, days, weeks or longer. When smokers quit they should take steps to rid their homes and vehicles of thirdhand smoke. This is potentially a time-consuming and expensive proposition but it is worth doing.

In 2011, 44 million American adults smoked cigarettes and 34 million of them smoked every day. Smoking causes 1 in 5 deaths, killing nearly 500,000 people in the U.S. every year — more than HIV, illegal drugs, alcohol, motor vehicle accidents and firearms combined. Is it really worth it?

Professors Norbert Herzog and David Niesel are biomedical scientists at the University of Texas Medical Branch. Learn more at