A “burnt hit” or “dry hit” is a common and intensely unpleasant experience for users of nicotine delivery systems. The immediate reaction involves a harsh, acrid taste, intense coughing, and severe throat irritation. Inhaling this altered vapor is detrimental to health, as the danger stems from specific chemical changes occurring inside the device.
The Mechanism of Thermal Degradation
A burnt hit originates from a physical failure within the atomizer called “dry wicking.” This occurs when the cotton or synthetic wick material surrounding the heating coil does not contain enough e-liquid to keep the coil saturated. When the device is activated, the coil rapidly heats up without the cooling effect provided by liquid vaporization.
This lack of liquid causes the coil temperature to spike far beyond the normal operating range, often exceeding 300 degrees Celsius. At these extreme temperatures, the primary e-liquid components, Propylene Glycol (PG) and Vegetable Glycerin (VG), undergo a structural change. This intense heat initiates thermal degradation, which breaks down the complex molecules into simpler, volatile, and hazardous compounds. This mechanism is fundamentally different from the normal process of vaporization, which merely turns the liquid into an aerosol.
Specific Toxic Compounds Released
Thermal degradation transforms the relatively benign PG and VG molecules into a variety of harmful substances, primarily known as carbonyl compounds. These aldehydes are formed when high temperatures cleave the molecular backbones of the e-liquid components. The resulting vapor contains substances that are not present during normal operating conditions.
One of the most concerning byproducts is Acrolein, a highly reactive and intensely irritating aldehyde. Acrolein is responsible for the characteristic acrid smell and the immediate, painful throat irritation associated with a burnt hit. Its chemical structure makes it particularly adept at reacting with biological molecules in the respiratory tract, disrupting cellular function upon contact.
Another significant compound formed under these conditions is Formaldehyde, which is classified as a known human carcinogen. Research shows that the concentration of Formaldehyde increases exponentially when the coil temperature rises above the recommended operational limits. Inhaling this chemical introduces a recognized threat directly into the lungs.
The extremely high temperatures also exacerbate the leaching of metallic ions from the heating elements. Coils constructed from materials like Nichrome or Kanthal may release trace amounts of metals such as Nickel, Chromium, and Manganese into the inhaled aerosol. Exposure is magnified during a burnt hit due to the increased rate of material erosion at excessive temperatures.
Acute Respiratory and Cellular Damage
The immediate biological response to inhaling the vapor from a burnt hit is an acute, corrosive irritation of the respiratory system. High concentrations of Acrolein and Formaldehyde rapidly attack the delicate mucous membranes and epithelial cells lining the airways. This exposure causes damage significantly more severe than the minor throat irritation sometimes experienced during normal nicotine inhalation.
Acrolein acts as a potent irritant, causing immediate symptoms like severe coughing, a burning sensation in the throat and lungs, and chest tightness. This highly reactive chemical readily forms adducts with proteins and DNA within the cells of the respiratory tract. The body attempts to forcefully expel these irritants through reflexive coughing to prevent further penetration into the lungs.
At the cellular level, these highly reactive molecules induce oxidative stress and inflammation. The epithelial barrier, which protects the underlying lung tissue, becomes compromised and damaged. This acute cellular stress can lead to temporary impairment of the lungs’ defense mechanisms, making the airways more susceptible to infection and long-term damage with repeated exposure to the burnt aerosol.
Preventing Burnt Hits and Coil Failure
Avoiding the harmful effects of a burnt hit requires adherence to proper device maintenance and usage habits. The first preventative measure is ensuring proper coil priming before the first use of a new heating element. This involves dripping e-liquid onto the exposed cotton ports and allowing the fully assembled coil to soak in a filled tank for several minutes, guaranteeing complete saturation of the wick.
Users must consistently monitor the level of e-liquid inside the tank or pod system. Running the device until the liquid reservoir is nearly empty is the primary cause of dry wicking and should be avoided. Maintaining a visible liquid level ensures the capillary action can continuously draw liquid onto the coil, preventing the cotton from drying out.
Operating the device within the manufacturer’s recommended power settings also prevents excessive thermal stress. Coils are designed to operate optimally within a specific wattage range. Exceeding this limit forces the heating element to vaporize liquid too quickly, leading to premature drying of the wick and subsequent thermal degradation.