Secondhand Smoke: Health Risks and Prevention

What is secondhand smoke (passive smoking)?

SHS is the involuntary inhalation of smoke from burning tobacco products, often exhaled by smokers. It comprises of two distinct types:^[4][5]

• Sidestream smoke: Smoke directly emitted from the burning end of a cigarette, cigar, or pipe. It constitutes about 85% of SHS and contains higher concentrations of carcinogens (chemicals known to cause cancer), like benzene (which is linked to leukemia) and formaldehyde (a chemical used in embalming), due to incomplete combustion.
• Mainstream smoke: This is smoke exhaled by the smoker after inhalation.

Unlike firsthand smoke, SHS lacks filtration, meaning bystanders inhale unfiltered toxins. For example, sidestream smoke contains three times more carbon monoxide (a gas that reduces oxygen delivery to organs) and 10–30 times more ammonia (a lung irritant) than firsthand smoke.^[1]

Health risks of secondhand smoke

Short-term effects:^[1]

• SHS exposure can cause bronchiolitis (specifically in children) and manifest as these respiratory symptoms: cough, phlegm, wheezing, and breathlessness.
• SHS increases the number of asthma attacks and the severity of asthma in children.
• Nonsmokers exposed to SHS experience more sick days due to respiratory infections, such as bronchitis and pneumonia.

Long-term effects:^[1][2][3][5]

• Cardiovascular disease (heart disease): SHS damages the lining of blood vessels (called the endothelium), increases low-density lipoprotein (LDL) cholesterol (which is the more high-risk type of cholesterol), and raises heart disease risk by 25–30%—equivalent to smoking 1–4 cigarettes daily.
• Lung cancer: Statistics indicate that lung cancer accounts for 7,300 annual U.S. deaths among nonsmokers, with a 20–30% higher risk for those regularly exposed.
• Childhood risks: SHS is linked to sudden infant death syndrome (SIDS), low birth weight, and developmental delays. For example, infants exposed to SHS are twice as likely to die from SIDS.
• Chronic conditions: SHS decreases lung function in patients who have chronic obstructive pulmonary disease (COPD) and can worsen diabetes severity by increasing insulin resistance.

How long does secondhand smoke stay in your system?

SHS exposure leads to the absorption of nicotine, which is metabolized into cotinine, a biomarker commonly used to detect nicotine exposure. Following brief exposure, cotinine can be detected in blood, saliva, and urine for 2 to 4 days in most people, and it can be detected in hair for 90 days.^[8] However, chronic or heavy exposure may prolong the detection of cotinine in bodily fluids, lasting even for a week in certain people.^[9]

Additionally, studies on detecting cotinine in urine report that measurable levels of urinary cotinine may vary based on factors like exposure intensity, metabolic rate, and passive smoking exposure. In most cases, children retain detectable cotinine levels longer than adults.^[10][26] In rare instances of sustained exposure, cotinine can stay in urine for over a week before being eliminated.^[10].

Myths and misconceptions about secondhand smoke

“If it doesn’t smell, it isn’t harmful.”

This is a myth. Carbon monoxide (CO) is an odorless gas that binds to hemoglobin, impairing oxygen transport, decreasing oxygenation in organs and tissues, and causing oxidative stress. High levels of oxidative stress occur when there is an imbalance of free radicals and antioxidants in the body, which is known to cause cell and tissue damage.^[11] Additionally, ultrafine particles (PM2.5) are invisible, yet they are still able to penetrate the lung alveoli, promoting systemic inflammation and oxidative damage.^[12]

“Outdoor exposure is safe.”

This is incorrect. Outdoor SHS exposure in semi-enclosed spaces (like patios or bus stops) can reach harmful levels, especially within 3–6 feet of a person smoking. For example, outdoor restaurant smoking sections have shown PM2.5 concentrations comparable to indoor bars.^[13] Additionally, general SHS exposure outdoors in crowded or partially enclosed areas remains a significant health risk.^[14]

“Vaping is harmless to bystanders.”

This is a misconception. E-cigarette aerosol contains harmful chemicals, including nicotine, volatile organic compounds (such as acrolein, which is a lung irritant), and heavy metals (like lead and nickel).^[15] Research shows that bystanders exposed to e-cigarette emissions in confined spaces absorb nicotine, volatile chemicals, and fine particles, which then cause irritation and systemic effects.^[16] Additionally, short-term exposure to vaping in confined spaces (like cars) can affect respiratory health.^[17]

How to protect yourself and others from secondhand smoke

• Create and maintain smoke-free environments: Make your home and car smoke-free to eliminate exposure for you, your family, and visitors. Studies prove that indoor environments are the primary source of prolonged SHS exposure, leading to respiratory and cardiovascular risks.^[10]
• Avoid semi-enclosed outdoor spaces: Be cautious in areas like patios, bus stops, or outdoor restaurants. SHS can still reach harmful concentrations, even within 3–6 feet of a smoker.^[14] Choose smoke-free outdoor areas whenever possible.
• Advocate for and support smoke-free policies: Supporting workplace and public area smoking bans significantly reduces exposure to SHS and improves air quality.^[13] Comprehensive smoke-free laws are effective in lowering SHS health risks.
• Use air purification systems cautiously: Some air purifiers do not entirely eliminate the toxic components of SHS.^[16] The best protection is complete avoidance.
• Educate others about the risks: Share information about the dangers of SHS, including the risks of both short-term and long-term exposure, such as respiratory illnesses, cardiovascular diseases, and cancers.^[18]
• Protect children and vulnerable people: Children, pregnant women, and those with pre-existing conditions (like asthma) are particularly vulnerable to SHS. Create and remain in designated smoke-free zones and avoid exposing them to environments with residual smoke.^[19]

When to seek help for secondhand smoke exposure

• If you experience persistent respiratory symptoms: Seek medical help if you experience persistent coughing, wheezing, shortness of breath, or chest tightness. SHS exposure can trigger and exacerbate respiratory infections and conditions.^[20]
• If you develop cardiovascular symptoms: Although nonspecific, symptoms such as chest pain, palpitations, or fatigue could indicate cardiovascular stress caused by SHS exposure.^[11]
• If you notice chronic symptoms in children: Children are particularly vulnerable to SHS. Seek help if your child shows signs of frequent colds, ear infections, or respiratory infections, as these are commonly associated with SHS exposure.^[19] Persistent wheezing or breathing difficulties may require urgent attention.
• In case of pregnancy-related complications: Pregnant women exposed to SHS should seek medical advice if they experience unexplained bleeding, decreased fetal movement, or early contractions. SHS is a risk factor for low birth weight and pregnancy complications.^[15]
• If you or a family member experience symptoms of toxic exposure: Exposure to high concentrations of SHS in poorly ventilated areas can cause symptoms like dizziness, nausea, and confusion due to CO inhalation. Seek help immediately if these symptoms appear.^[16]
• For support in quitting smoking to reduce exposure: If you or someone in your household smokes and you are concerned about SHS exposure, seek professional counseling, nicotine replacement therapy, or cessation programs to minimize risks to others.^[10]

Treatment options for nicotine addiction

• Nicotine replacement therapy (NRT): NRT delivers controlled doses of nicotine without harmful chemicals found in tobacco smoke, helping to alleviate withdrawal symptoms and reduce cravings.^[21]
• Prescription medications: Bupropion (Zyban) and varenicline (Chantix) are FDA-approved medications for smoking cessation.^[22]
• Behavioral therapy and counseling: Cognitive-behavioral therapy (CBT) and motivational interviewing (MI) can address psychological dependence by identifying triggers and building coping mechanisms.^[23]
• Mobile apps and digital support programs: Digital interventions, like smoking cessation apps, text message programs, and online forums, provide around-the-clock support.^[24]
• Support groups and peer networks: Programs like Nicotine Anonymous (NA) offer peer support and accountability through group meetings.
• Combination therapy: Combining NRT with behavioral therapy or medications proves to be the most effective strategy for smoking cessation by addressing both the physical and psychological aspects of nicotine addiction.^[21]
• Alternative therapies: Though evidence is limited, some people report success using acupuncture, mindfulness meditation techniques, or hypnosis as complementary approaches to mainstream treatments.^[25]

The most effective approach often involves a combination of NRT, behavioral therapy, and medications tailored to individual needs. Seeking guidance from a healthcare provider can help identify the best treatment plan.