has been attributed to veterans being exposed to trash burn pits. Veterans present with shortness of breath and other asthma-like symptoms. The only way to diagnose this condition is by doing a lung biopsy as chest X-rays and CT scans come back as normal. The government still denies that there is any correlation between burn pits and health problems but the government has started an "Airborne Hazards and Open Burn Pit Registry" to begin tracking the health of veterans who were exposed to burn pits to see if there is a connection. E-cigarettes The American Lung Association lists flavored e-cigarettes as a risk in 2016. Health Canada has, however seen no cases as of 2019. Public Health England writes that the association has come about as "some flavourings used in e-liquids to provide a buttery flavour contain the chemical diacetyl... however, diacetyl is banned as an ingredient from e-cigarettes and e-liquids in the UK." Mechanism The underlying mechanism involves injury and inflammation of epithelial and sub-epithelial cells. These cells then lose the ability to repair the tissue, in particular they lose the ability to regenerate the epithelial or outermost layer, leading to the excess growth of cells that cause scarring. There are multiple pathways of the disease including fibrotic, lymphocytic, and antibody-mediated that have been described. However, while each pathway has a more unique starting point and cause, the result is still injury and inflammation leading to scarring of the lung tissue. The scarred tissue then makes the expiration phase of respiration more difficult, leading to air not being expelled from the lungs. This is termed "air-trapping", which can be seen on medical imaging. Since the scarring is non-reversible, the disease generally does not improve over time, and depending on the inciting can progress to death. Diagnosis Bronchiolitis obliterans is often diagnosed based on the symptoms of obstructive lung disease following lung injury. The definitive diagnosis is through biopsy, but due to the variable distribution of lesions, leading to falsely negative tests, and invasive nature of this procedure it is often not performed. Several tests are often needed to diagnose bronchiolitis obliterans, including spirometry, diffusing capacity of the lung tests (DLCO), lung volume tests, chest X-rays, high-resolution CT (HRCT), and lung biopsy. Pulmonary function testing Spirometry tests usually show an obstructive pattern and is the most common presentation. A slightly reduced to normal forced vital capacity (FVC), and a reduced