Is vapor harmful?

Yes, the "vapor" (which is actually aerosol) produced by e-cigarettes is harmful.

It is definitely not the "harmless steam" that some merchants sometimes claim, but rather a complex mixture of various harmful and potentially harmful substances. The Centers for Disease Control and Prevention (CDC) in the United States has also clearly stated that no tobacco product (including e-cigarettes) is safe.

What is in e-cigarette aerosol?
The aerosol produced by heating the e-liquid in e-cigarettes typically contains the following harmful or potentially harmful substances:

Nicotine: A highly addictive substance that damages the brain development of teenagers, is toxic to fetal development, and can lead to elevated blood pressure and increased heart rate.

Carcinogenic chemicals: Such as formaldehyde and acetaldehyde, these substances are known or potentially carcinogenic. A study even found that the formaldehyde concentration in some e-cigarettes may be higher than that of regular cigarettes.

Heavy metals: From the heating elements of the device, such as lead, nickel, chromium, and tin. Inhaling these metals can have an impact on cardiovascular and respiratory health.

Ultrafine particles: With a particle size smaller than PM2.5, they can penetrate deep into the deepest part of the lungs, induce inflammation, and be associated with risks such as hypertension and heart disease.

Other toxic substances: Such as propylene glycol and vegetable glycerin (which can produce toxic compounds when heated), as well as diacetyl used for flavoring, which is associated with a severe and irreversible lung disease called "popcorn lung".

What are the specific health hazards?
Inhalation of these harmful substances can have multiple impacts on health:

Lung damage: This is the most direct harm. The aerosol damages the functions of immune cells in the lungs (such as macrophages), induces inflammation, and may lead to asthma, chronic airway inflammation. In severe cases, it may cause a serious disease called EVALI (E-cigarette or Vaping Product Use-Associated Lung Injury), with symptoms including shortness of breath, coughing, fever, and even respiratory failure and death. As of November 2019, the CDC reported over 2,000 cases of related cases.

Cardiovascular effects: Nicotine and ultrafine particles and other substances can cause elevated blood pressure, increased heart rate, and impaired vascular function, increasing the risk of heart disease and heart attack.

Oral health problems: Using e-cigarettes is associated with gum inflammation, changes in the oral microbiome, periodontal disease, and oral infections.

Nicotine addiction and brain development: The high addictionability of nicotine makes users (especially teenagers) quickly addicted and damages the areas of the brain responsible for attention, learning, emotion, and impulse control.

❓ What are the "unknown" risks
E-cigarettes are a relatively new product, and its long-term health effects (such as what will happen after 10 or 20 years of use) are currently unclear. The scientific community is still studying all its hazards.

Impact on people around (second-hand aerosol)
The harm of e-cigarettes is not limited to the users themselves. Bystanders (people around) inhaling the aerosol exhaled by others also have health risks, as it contains harmful substances such as nicotine, ultrafine particles, and carcinogens.

In conclusion, the aerosol of e-cigarettes is far from harmless steam. It contains various known or suspected harmful chemicals and is closely related to lung damage, cardiovascular problems, nicotine addiction, and many other health risks.