The Dangers of Secondhand Smoke

Secondhand smoke is a mixture of two forms of smoke that come from burning tobacco:

• Sidestream smoke: Smoke from the burning tip of a cigarette, cigar, or pipe. This is actually more toxic than the smoke inhaled by the smoker, because it burns at a lower temperature and is not filtered.
• Mainstream smoke: The exhaled smoke breathed out by a smoker.

According to the CDC, secondhand smoke contains more than 7,000 chemicals, of which at least 70 are known to cause cancer. These include:

• Benzene, formaldehyde, and vinyl chloride (carcinogens)
• Carbon monoxide (reduces oxygen in the blood)
• Ammonia, hydrogen cyanide, and arsenic
• Nicotine (the addictive compound)

The chemicals in secondhand smoke do not disappear when a cigarette is extinguished. They linger in the air for hours and settle on surfaces and fabrics - a phenomenon sometimes called "thirdhand smoke" - where they continue to pose risks, particularly to young children who crawl on floors and put objects in their mouths.

Non-smoking adults who are regularly exposed to secondhand smoke face significantly elevated risks of serious disease. The evidence is robust and consistent across multiple large studies reviewed by the CDC, WHO, and American Cancer Society (ACS):

• Heart disease: Exposure to secondhand smoke increases the risk of coronary heart disease by 25–30%. The chemicals in secondhand smoke damage blood vessels, promote the build-up of fatty deposits in arteries (atherosclerosis), and make blood more likely to clot. Even brief exposure can affect the cardiovascular system.
• Lung cancer: Non-smokers exposed to secondhand smoke at home or at work have approximately a 20–30% increased risk of developing lung cancer compared to non-smokers without such exposure. The ACS estimates that secondhand smoke causes approximately 7,300 lung cancer deaths among non-smokers in the US every year.
• Stroke: Secondhand smoke exposure is associated with an increased risk of stroke, due to its effects on blood vessel health and clotting.
• Respiratory disease: Exposure worsens existing conditions such as asthma and COPD, and increases the frequency and severity of respiratory infections.

The WHO estimates that secondhand smoke causes approximately 1.2 million premature deaths per year globally - around 28% of all tobacco-related deaths.

Children are particularly vulnerable to secondhand smoke because their lungs and immune systems are still developing, they breathe more rapidly than adults (inhaling more air - and more pollutants - per unit of body weight), and they have less control over their environment.

Exposure to secondhand smoke in children is linked to:

• Sudden Infant Death Syndrome (SIDS): Babies exposed to secondhand smoke after birth face a significantly higher risk of SIDS. The CDC identifies parental smoking as a major modifiable risk factor for SIDS.
• Asthma: Children of parents who smoke are more likely to develop asthma. In children who already have asthma, secondhand smoke exposure triggers more frequent and severe attacks.
• Ear infections: Secondhand smoke increases the risk of middle ear infections (otitis media) and related hearing problems in children.
• Respiratory infections: Children exposed to secondhand smoke are more likely to develop bronchitis, pneumonia, and other lower respiratory tract infections.
• Impaired lung development: Regular exposure during childhood can permanently impair lung development, reducing lung capacity and function into adulthood.
• Meningitis: Some studies link secondhand smoke exposure to an increased risk of bacterial meningitis in children.

The American Academy of Pediatrics advises that there is no safe level of secondhand smoke exposure for children. The only effective protection is to create a completely smoke-free environment.

The only way to fully protect non-smokers from the effects of secondhand smoke is to eliminate smoking in the spaces they occupy. Ventilation, air purifiers, and smoking near open windows do not eliminate the risk - the chemicals still circulate and settle on surfaces.

Practical steps to reduce exposure:

• Make your home smoke-free: Ask anyone who smokes not to smoke inside your home, including in rooms that children do not currently occupy - chemicals spread throughout the house.
• Make your car smoke-free: Secondhand smoke concentrations in cars can be extremely high, even with windows open. In many countries, smoking in a car with children present is illegal.
• Choose smoke-free venues: Smoke-free legislation in many countries has dramatically reduced public exposure, but some outdoor areas and private spaces still present risk.
• Encourage smokers around you to quit: The most effective long-term solution. Resources like NHS Stop Smoking Services, the CDC's 1-800-QUIT-NOW line, and QuitSmokeApp can help.

If you are a smoker, quitting is the single most effective thing you can do to protect the health of the people around you - particularly your children and partner.