Secondhand smoke is the smoke exhaled from a smoker’s lungs and the smoke created by a burning cigarette, cigar, or pipe. It is also known as passive or involuntary smoking, tobacco smoke pollution, or environmental tobacco smoke. Cigars create more secondhand smoke than cigarettes because they have more tobacco and burn longer.
Secondhand smoke and disease
Breathing secondhand smoke is basically like smoking, which is why it is called passive or involuntary smoking. Tobacco smoke has many harmful substances. These include benzopyrene, lead, carbon monoxide, arsenic, ammonia, formaldehyde, and a type of cyanide. Many of these cancer-causing substances stay in the air and go into the lungs and bloodstream.
According to the U.S. Surgeon General, there is no safe level of exposure to secondhand smoke. Even brief moments around smoke can be harmful to a person’s health. And, the risk of health problems increases with more exposure to secondhand smoke. The U.S Surgeon General estimates that living with a smoker increases the chance of getting lung cancer  by 20% to 30%. Research has not yet proved that secondhand smoke causes cancers other than lung cancer. However, the research does suggest that secondhand smoke exposure may increase the risk of some other cancers by at least 30%. These other cancers include cervical cancer, kidney cancer, nasopharyngeal cancer, rectal cancer, and brain tumors.
Secondhand smoke also causes many other health problems, such as asthma and heart disease. Pregnant women, older adults, and people with breathing conditions and heart disease have a higher risk of negative health effects from secondhand smoke. As with smoking, exposure to secondhand smoke negatively affects people right away, causing lung inflammation and depleting important vitamins. These effects of secondhand smoke can make people more likely to develop health problems.
Health risks to children from secondhand smoke
Secondhand smoke is especially unsafe for babies and young children because their bodies and lungs are still developing. For children, secondhand smoke exposure raises the risk of the following conditions:
Lung infections, such as bronchitis and pneumonia
Coughing and wheezing
Sudden infant death syndrome (SIDS)
Ongoing research shows additional links between secondhand smoke and child well-being. For example, children exposed to secondhand smoke may be more likely to have mental health issues and problems with learning. Also, children who are around adults who smoke are much more likely to become smokers themselves.
How to avoid secondhand smoke
When someone smokes indoors, it is not enough to keep the smoke away by opening a window or using a fan. In fact, research indicates that toxins from smoke remain in a person’s hair and clothes or in carpets and furniture. These toxins, often called “thirdhand smoke,” are also hazardous to infants and children.
The only way to avoid the risks of smoke is to avoid places where smoking occurs. Here are additional ways to protect yourself and your family from secondhand smoke:
Keep your home and car smoke-free by making sure family, friends, and visitors never smoke inside your house or vehicle. Ask smokers to step outside.
Many state and local governments require workplaces to be smoke-free. However, if your workplace does not ban smoking, ask for a smoke-free workplace that would ban smoking indoors.
If your state or local government does not currently require smoke-free workplaces, choose to eat in restaurants that are smoke-free. Nonsmoking sections do not provide protection from secondhand smoke.
When you travel, stay in smoke-free hotels and rent smoke-free cars.
Make sure the places where your child spends time, such as daycare, school, or after-school programs, do not allow smoking. Ask caregivers and relatives never to smoke around your children.
If you smoke, quit. Quitting can be difficult, but there are many resources to help you . Talk with a doctor or a nurse about the best options to help you quit.
Smoke-free workplace laws
Experts say that the only way to completely protect people from secondhand smoke is to ban smoking indoors. Smoke-free workplace laws have helped reduce exposure to secondhand smoke and the related health problems without hurting the economy. Most states have passed laws banning or limiting smoking in public places, including the workplace. In addition, almost half of the states and Washington, D.C., do not allow smoking in restaurants and bars. Many counties and cities also have smoke-free laws. Find out more about your state’s smoking laws .
Types of Cancer 
Centers for Disease Control and Prevention: Secondhand Smoke Facts 
National Cancer Institute: Secondhand Smoke and Cancer