Walk into any vape shop and you will see a wall of flavors that reads like an ice cream parlor menu: mango chill, cotton candy, crème brûlée, blue razz. The labels look harmless, sometimes even wholesome. That contrast is the hook. Most people who switch to vaping do it for the nicotine, the ritual, or to move away from smoke. They rarely come for the chemistry lesson. Unfortunately, that is what decides what happens in your lungs.

I have spent a fair bit of time in clinics with patients who vape, and in labs with scientists who analyze aerosol. The gulf between how vapes are marketed and what they deliver is wide. If you want to understand vaping health risks with adult seriousness, especially around flavorings and lung damage, you need to know what is being heated, what forms in that vapor, and how your airways respond to the mixture.

Flavor is not just taste, it is chemistry

The word “flavor” sounds simple. In e-liquids, it usually means a blend of food-grade aromatic compounds dissolved in a base of propylene glycol and glycerin. “Food-grade” is doing far too much work in that sentence. Safety for swallowing does not equal safety for inhaling. Your gut has enzymes and barriers designed for digestion. Bronchi and alveoli are thin, delicate membranes that depend on a lining of surfactant and cilia to keep air moving and pathogens out.

Many common flavoring agents were designed for candy, bakery, or beverages. For example, cinnamaldehyde delivers cinnamon warmth on the tongue. Menthol cools. Vanillin mimics vanilla. Fruit flavors often rely on esters like ethyl butyrate or ethyl maltol for sweetness. All of these can irritate airway cells once they are aerosolized. Dose, heat, and solvent matter. When these compounds are heated by a vape coil, they can degrade or react, creating new chemicals that were never tested for inhalation.

A concrete example: vanillin and ethyl maltol can produce acetals when mixed with propylene glycol. Those acetals have been found to be more reactive with airway cells than the original flavors. Another: cinnamaldehyde has repeatedly been shown to impair cilia beating in lab models. Cilia are the tiny hairlike structures that move mucus out of the lungs. Slow them, and you reduce your lungs’ housekeeping.

The base matters: propylene glycol and vegetable glycerin

Propylene glycol (PG) and vegetable glycerin (VG) carry flavor and nicotine. PG is thin, carries flavor well, and gives a “throat hit.” VG is thicker, produces denser clouds, and feels smoother. Both are generally recognized as safe to swallow. Inhalation is a different story. Neither PG nor VG is inert when heated, and the higher the device power and coil temperature, the more breakdown products you get.

Thermal decomposition of PG and VG can generate formaldehyde, acetaldehyde, and acrolein. In real-world conditions, the levels vary widely, depending on the device, voltage, coil age, and puffing behavior. Formaldehyde and acrolein are respiratory irritants. Acrolein in particular has a reputation as a potent ciliotoxin and causes cough, chest tightness, and wheeze at sufficient concentrations. If you have ever taken a dry hit that scorched your throat, you got a big dose of thermal degradation products.

This is one of the reasons people report different vaping side effects across devices. A compact pod at standard settings might deliver fewer carbonyls https://docs.google.com/spreadsheets/d/1t-pyMhwbqWw4GVyQ294DmNKEhM6tpprS2OsQ1vmhHNs/edit?usp=sharing than a high-wattage mod with sweet, sticky liquids, especially if the coil is old. That does not mean low-wattage devices are safe. It means device settings shift the risk profile.

Diacetyl, its cousins, and the “popcorn lung” story

Popcorn lung vaping became a headline after investigators found diacetyl, the buttery flavor chemical linked to bronchiolitis obliterans in factory workers who inhaled high levels during microwave popcorn production. Bronchiolitis obliterans is scarring of the smallest airways that leads to fixed airflow obstruction. It is not asthma, and it does not reverse with inhalers. The colloquial name stuck because of the popcorn factory outbreak.

When researchers started testing e-liquids, they found diacetyl and 2,3-pentanedione in some buttery, creamy, and caramel flavors. Levels varied widely, and many companies subsequently reformulated or claimed to remove these compounds. The nuance: even when diacetyl is absent, other diketones can be present, and labeling is inconsistent. Some studies still detect diacetyl-like compounds in certain liquids or identify them after thermal decomposition. The risk is not binary, safe or unsafe. It is about cumulative exposure an

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