Airway inflammation is a key feature of many respiratory conditions like asthma, chronic obstructive pulmonary disease (COPD), and respiratory infections. When the airways become inflamed, it can cause coughing, wheezing, chest tightness, and shortness of breath. Understanding what triggers airway inflammation is important for managing these respiratory conditions. There are several factors that can initiate and worsen inflammation in the airways.
One of the most common triggers of airway inflammation is exposure to allergens. An allergen is a normally harmless substance that provokes an immune reaction in people who are sensitized to it. Common inhaled allergens include:
- Dust mites
- Pet dander
When an allergic person inhales one of these allergens, it triggers immunoglobulin E (IgE) antibodies to release inflammatory mediators like histamine. This causes constriction of the airways, production of mucus, and local inflammation. In people with asthma, allergies are a major cause of flare-ups and worsening of symptoms.
Dust mites are microscopic insects that live in dust and fabrics. They feed on flakes of human skin cells and produce allergens that can trigger reactions. Dust mite allergy is extremely common and exposure to mites in bedding is a frequent cause of nighttime asthma symptoms. Controlling dust mites through washing bedding in hot water weekly and removing carpeting can help reduce airway inflammation.
Pet dander refers to tiny flakes of skin or protein from the fur, feathers, or hair of animals. Dander particles are light and easily inhaled. Allergies to dander from cats, dogs, rodents, and birds are common triggers for asthma and inflammation. Keeping pets out of the bedroom and using HEPA air filters can decrease dander exposure.
Many plants release tiny pollen grains into the air for reproductive purposes. Inhaling pollen from trees, grasses, and weeds provokes allergic reactions in sensitized individuals. Pollen allergies are seasonal and highest during the spring, summer, and fall. Staying indoors when pollen counts are high and using medication can help control pollen-induced airway inflammation.
Mold spores are microscopic particles released by mold fungi. Inhaling spores from household molds or outdoor molds can cause allergic reactions. Damp areas of the home like basements are prone to mold growth. Fixing water leaks, cleaning with bleach, and using a dehumidifier can help reduce mold and related airway inflammation.
Viral and bacterial respiratory tract infections are another major cause of airway inflammation. Infections lead to inflammation through:
- Direct damage to airway epithelial cells
- Immune responses to the pathogen
- Secondary bacterial infections following an initial viral infection
Common respiratory pathogens that trigger inflammation include influenza, respiratory syncytial virus (RSV), rhinovirus, adenovirus, coronavirus, Mycoplasma pneumoniae, and Streptococcus pneumoniae. The inflammation makes symptoms worse and last longer. Antiviral medications, antibiotics, and rest help resolve infection-related airway inflammation.
The influenza virus infects and destroys cells along the respiratory tract, provoking widespread airway inflammation. Influenza also impairs the immune response, leading to secondary bacterial pneumonia which further worsens inflammation. Getting an annual flu vaccine helps prevent influenza infections and related inflammation.
Respiratory Syncytial Virus
RSV is a common cause of bronchiolitis and pneumonia in infants and children. The virus damages and kills epithelial cells lining small airways, causing significant inflammation. RSV often leads to wheezing and worsening of asthma symptoms. A medication called palivizumab can help prevent severe RSV infections in high-risk infants.
Rhinoviruses are the viruses that cause about 50% of common colds. Rhinovirus colds frequently spread to the lower airways causing tracheitis, bronchitis, and exacerbations of asthma and COPD. There are no effective treatments for rhinovirus infections besides symptom relief. Good hand hygiene helps prevent spread of rhinoviruses.
Air pollutants and chemicals that irritate the respiratory tract epithelia directly can instigate airway inflammation through release of inflammatory neuropeptides and cell damage. Common environmental triggers include:
- Cigarette smoke
- Industrial pollutants
- Cleaning products and chemicals
- Wood smoke
- Traffic-related air pollution
Avoiding or reducing exposure to these irritants can help prevent inflammation. Wearing an N95 mask when exposed to pollution or chemicals may also decrease irritation.
Cigarette smoke contains thousands of chemicals that damage airway cells and provoke inflammation through oxidative stress pathways. Both firsthand and secondhand tobacco smoke trigger airway inflammation. Quitting smoking is essential for reducing inflammation in smokers.
Air pollution from industrial sources like factories, refineries, and power plants contain tiny particles and gases like ozone, nitrogen oxides, and sulfur oxides. These pollutants cause oxidative damage and inflammation when inhaled. Stricter regulation of industrial emissions has improved air quality in many regions.
Many household cleaners and products like bleach, degreasers, and spray detergents release volatile organic compounds that irritate the airways when inhaled. Limiting use of harsh cleaning chemicals or replacing them with milder products can decrease exposure. Always ensure proper ventilation when using any chemical products.
Some medications can provoke inflammation along the respiratory tract as an adverse side effect. This is most commonly seen with nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin or ibuprofen, especially in people with asthma. Other drugs that may cause airway inflammation include:
- Angiotensin-converting enzyme (ACE) inhibitors
- Certain chemotherapy agents
- Monoclonal antibodies
People who experience respiratory symptoms with any medication should talk to their doctor about safer alternatives or strategies to manage inflammation.
Aspirin and NSAIDs
A subset of people with asthma develop worsening of symptoms and airway inflammation in response to aspirin or other NSAIDs. This condition is called aspirin-exacerbated respiratory disease (AERD). It is caused by shunting of arachidonic acid into the production of inflammatory leukotrienes when the COX-1 enzyme is inhibited. Avoiding aspirin and NSAIDs helps prevent this reaction.
Angiotensin-converting enzyme (ACE) inhibitors are commonly used to treat high blood pressure. A dry cough is a frequent side effect due to buildup of inflammatory bradykinins. People may need to switch to an angiotensin receptor blocker (ARB) instead to control their blood pressure without the cough.
Stress and Emotions
Psychological stress and emotions like anxiety can trigger airway inflammation through activation of the nervous system. This leads to release of inflammatory neuropeptides like substance P and neurokinins from nerve fibers. Managing mental health and using relaxation techniques helps control stress-related airway inflammation.
Anxiety activates the sympathetic nervous system, leading to increased airway resistance and inflammation. Treating underlying anxiety disorders and using cognitive behavioral therapy and medications can help reduce airway symptoms.
Ongoing stressors lead to systemic inflammation through elevated cortisol, cytokines, and oxidative stress. This can worsen inflammatory airway conditions. Regular exercise, sufficient sleep, and stress management help counteract the effects of chronic stress.
Fluctuations in hormones can exacerbate respiratory inflammation in some situations:
- Worsening of asthma during menstruation in women
- Increased inflammation during pregnancy
- Onset of late-onset asthma during menopause
The exact mechanisms relating hormonal changes to airway inflammation are not fully understood. Managing respiratory conditions carefully during periods of hormonal changes is important.
Many women experience premenstrual worsening of asthma symptoms due to declining progesterone levels. Progesterone has anti-inflammatory effects and protects the airways. Low levels right before menstruation allow increased inflammation.
Pregnancy leads to elevated levels of hormones like estrogen and progesterone which can worsen inflammation. Pregnant women with asthma need to closely monitor their condition and adjust medications as needed.
After menopause, dropping estrogen levels are associated with new late-onset asthma in some women. Hormone replacement therapy may help stabilize respiratory inflammation for these patients.
Being overweight or obese increases systemic inflammation and risk of airway hyperresponsiveness through several mechanisms:
- Greater oxidative stress
- Higher circulating cytokines
- Adipose tissue hormones and inflammation
- Insulin resistance
- Gastroesophageal reflux
Losing weight through diet and exercise leads to improvement in respiratory inflammation and asthma control in obese patients. Even a small amount of weight loss can make a difference.
Some other factors that may contribute to worsening of airway inflammation include:
- Respiratory tract injuries or burns
- Gastroesophageal reflux
- Vocal cord dysfunction
- Obstructive sleep apnea
- Low vitamin D levels
Respiratory Tract Injury
Physical or chemical injuries to the airways from smoke inhalation, aspiration of caustic substances, or traumatic injury provokes severe local inflammation during the healing process.
Acid reflux from the stomach can cause microaspiration into the lower airways, inducing inflammation. Reflux is more common in pregnancy and being overweight. Proton pump inhibitors and weight loss help when reflux triggers respiratory inflammation.
Vocal Cord Dysfunction
This condition causes the vocal cords to inappropriately close and spasm when inhaling, leading to wheezing and airway obstruction. The repetitive trauma causes inflammation. Speech therapy helps retrain proper vocal cord motion.
Treating the Underlying Cause
The most effective way to treat airway inflammation is to eliminate or reduce exposure to the provoking trigger. This may include:
- Avoiding or reducing contact with allergens and irritants
- Treating underlying respiratory infections
- Stopping cigarette smoking
- Managing reflux, sleep apnea, and vocal cord dysfunction
- Trying alternative medications if drugs are the trigger
- Controlling stress and anxiety
- Losing weight if obese
Of course, avoiding triggers is not always possible. Inhaled corticosteroids and bronchodilators help reduce airway inflammation, constriction, and related symptoms, regardless of the cause. Leukotriene modifiers like montelukast also have anti-inflammatory effects. Biologic medications that target specific inflammatory pathways are newer options for severe refractory airway inflammation.
Airway inflammation is a key component of many chronic respiratory diseases and acute infections. A variety of triggers can instigate and worsen inflammation, including allergens, infections, irritants, hormones, obesity, stress, and more. Identifying and limiting exposure to relevant triggers, along with using controller medications, offers the best chance of controlling unwanted airway inflammation and related symptoms.