What is secondhand vapor (SHV), specifically referring to the aerosol released into the air by e-cigarettes or vaping devices after being exhaled by the user, and what are the known constituents of this SHV, including but not limited to nicotine, particulate matter, volatile organic compounds (VOCs), heavy metals, flavorings, and other potentially harmful substances? Furthermore, what is the current scientific understanding of the relative concentrations of these constituents in SHV compared to mainstream vapor (inhaled by the user) and secondhand smoke from traditional cigarettes, and what are the key methodological challenges in accurately measuring and characterizing SHV composition?

Answer

Secondhand vapor (SHV), also known as secondhand aerosol, is the aerosol emitted into the environment by electronic cigarettes (e-cigarettes) or vaping devices during use, and the aerosol exhaled by the user.

What Secondhand Vapor Contains:

SHV is not simply water vapor. It contains a complex mixture of potentially harmful substances, including:

• Nicotine: E-liquids usually contain nicotine, which is highly addictive. SHV exposes bystanders to nicotine, even if they are not vaping themselves. Nicotine exposure can have negative health effects, particularly on children and pregnant women.

• Ultrafine Particles: Vaping devices produce ultrafine particles that can be inhaled deeply into the lungs. These particles can irritate the respiratory system and potentially contribute to cardiovascular problems.

• Propylene Glycol (PG) and Vegetable Glycerin (VG): These are the base liquids used in e-liquids to create the visible vapor. While generally considered safe for ingestion in certain products, the long-term effects of inhaling aerosolized PG and VG are not fully understood. They can also cause respiratory irritation in some individuals.

• Flavoring Chemicals: E-liquids contain a wide variety of flavoring chemicals to create appealing tastes. Some of these chemicals, such as diacetyl (linked to popcorn lung), have been associated with serious respiratory illnesses. Other flavoring compounds can also cause irritation.

• Heavy Metals: Heavy metals, such as nickel, tin, lead, and chromium, can leach from the heating coil and other components of vaping devices into the aerosol. Exposure to these metals can have toxic effects on various organ systems.

• Volatile Organic Compounds (VOCs): VOCs are emitted during the heating process in vaping devices. Some VOCs, such as formaldehyde and acetaldehyde, are known carcinogens.

• Other Potentially Harmful Chemicals: Depending on the e-liquid and device, SHV may contain other potentially harmful chemicals, such as acrolein (a respiratory irritant) and various aldehydes.

The composition and concentration of these substances in SHV can vary depending on several factors, including:

• Type of E-cigarette or Vaping Device: Different devices have different heating mechanisms and materials, which can affect the composition of the aerosol.
• E-liquid Composition: The concentration of nicotine, flavoring chemicals, and other ingredients in the e-liquid will directly influence the composition of SHV.
• User’s Vaping Behavior: Factors such as puff duration, frequency of vaping, and device settings can affect the amount of aerosol produced and the concentration of harmful substances in SHV.
• Ventilation: Poorly ventilated environments can lead to higher concentrations of SHV.