Bronchitis is a condition characterized by inflammation of the bronchial airways--tubes that carry air in and out of the lungs and assist with breathing. Bronchitis can be acute, coming on suddenly and lasting a relatively short period of time, or it may be chronic, lasting for months at a time. Bronchitis is typically caused by infection from viruses or bacteria, but can also develop as a result of underlying medical conditions and exposure to allergens and toxic chemicals.
Viruses
Acute bronchitis is most commonly caused by viral infection of the bronchial tubes, according to FamilyDoctor.org. These viruses cause the tissues lining the airway to swell, making it more difficult to breathe. The respiratory syncytial virus (RSV) is a common cause of bronchitis and the most common cause of bronchiolitis--an infection of the tiny airways in the lung--among babies less than one year old, according to the Centers for Disease Control. The influenza virus, parainfluenza virus and adenovirus are also common causes of respiratory infections, including bronchitis.
Bacteria
Certain bacteria can invade the lungs and cause bronchitis. However, research indicates that bacteria are much less frequently responsible for the condition than doctors once believed, according to FamilyDoctor.org. Acute bronchitis in young adults can develop as a result of infection with mycoplasma pneumoniae or Chlamydia pneumoniae bacteria, according to Merck.com. Individuals with recent upper respiratory infections or whooping cough caused by the bordetella pertussis bacteria may also develop acute bronchitis.
Smoking
According to FamilyDoctor.org, cigarette smoking is the primary cause of chronic bronchitis. Inhaled smoke contains irritants that inflame the breathing airways and increase the production of mucus, leading to a cough, excess sputum and difficulties breathing. People who live in a household where others smoke and who breathe in second-hand smoke are also susceptible to developing bronchitis, according to the Mayo Clinic.
Acid Reflux
For people with certain digestive problems, stomach acid can sometimes flow backward into the esophagus, causing irritating of the lining of the food pipe. According to the Mayo Clinic, acid reflux and gastroesophageal reflux disease (GERD)--a chronic condition in which food, bile and stomach acid leak into the esophagus and cause persistent heartburn--may cause bronchitis.
Environmental Irritants
Exposure to substances in the environment that irritate the lining of the lungs can cause irritative, or environmental or industrial, bronchitis. According to Merck.com, individuals who inhale fumes from cleaning solutions and solvents that contain chemicals such as ammonia, sulfur dioxide, chlorine, hydrogen sulfide and bromine are more likely to develop bronchitis. Air pollution, smog and dust can also irritate the lining of the bronchial tubes and cause infection.
